I YOUNG

f UNIVERSITY

GEOLOGY STUDIES

r' Volume 12

C O N T E N T S

December 1965

Thrusting in the Southern Wasatch Mountains, Utah ........ Michael J. Brady 3

Nebo Overthrust, Southern Wasatch Mountains, Utah ........ B. Allen Black 55

Paleoecologic implications of Strontium, Calcium, and Magnesium in Jurassic rocks near Thistle, Utah .... Button W. Bordine 91

Paleoecology of the Twin Creek Limestone In the Thistle, Utah area .................................... .... . . . . . Ladell R. Bullock 121

Geolo of the Stockton stock and related intmsives, &1e County, Utah ................................................. John L. Lufkin 149

Stratigraphy and rifera of Ordovician rocks near Columbia I ceads , Jasper National Park, Alberta, Canada .............................................................. .. .... J. Keith Rigby 165

Lower Ordovician conodonts and other microfossils from the Columbia Icefields Section, Alberta, Canada ........................... .. .......... R. L. Ethington and D. L. Clark 185

..... Publications and maps of the Geology Department ........................... .. 207

Brigham Young University Geology Studies

Volume 1 2 - December 1965

Contents

Thrusting in the Southern Wasatch Mountains, Utah ........ Michael J. Brady 3

Nebo Overthrust, Southern Wasatch Mountains, Utah ........ B. Allen Black 55

Paleoecologic irriplications of Strontium, Calcium, and Magnesium in Jurassic rocks near Thistle, Utah .... Burton W. Bordine 91

Paleoecology of the Twin Creek Limestone in the .................................................... Thistle, Utah area Ladell R. Bullock 121

Geology of the Stockton stock and related intrusives, Tooele County, Utah .................................................... John L. Lufkin 149

Stratigraphy and porifera of Ordovician rocks near Columbia Icefields, Jasper National Park, Alberta, . . Canada .......................................................................... J. Kelth Rlgby 165

Lower Ordovician conodonts and other microfossils from the Columbia Icefields Section, Alberta, Canada ............................................ R. L. Ethington and D. L. Clark 185

Publications and maps of the Geology Department ........................................ 207

A publication of the

Department of Geology

Brlgham Young University

Provo, Utah 84601

Ed~tor

J. Keith Rigby

Editorial Staff

Lehi F. Hintze Myron G. Best

Brzgham Your~g Uniuerszty Geology Studres is published annually by the Department. Geology Studies consists of graduate student and staff research in the Department and occasional papers from other contributors, and is the successor to BYU Research Studies, Geology Serier, published in separate numbers from 1954 to 1960.

Distributed December 31, 1965

Prrce $4.00

Nebo Overthrust, Southern Wasatch Mountains, Utah*

ABSTRACT.-An overturned and in part recumbent anticline trends slightly east of north and forms the bulk of the Southern Wasatch Mountains north-east of Nephi, Juab County, Utah. Along the west flank of Mount Nebo, the west half of the fold is trun- cated by the normal Wasatch Fault whereas the southern extension is terminated by the Nebo Overthrust. The remaining easterly portion of the anticline is highly dissected and is partially covered by thick sequences of easterly dipplng Late Cretaceous and Tertiary sedimentary and volcanic rocks.

The Nebo Overthrust dips west to southwest at a low angle along the western margin of the mapped area, but it assumes an almost horizontal attitude near the center of the mountain range where overturned Paleozoic and Mesozoic rocks are in juxta- position with underlying Jurassic sandstones and shales. Slickensided surfaces in com- petent rocks near the main thrust zone, drag folds associated with minor thrusts in the Jurassic Arapien Shale, direction of overturning of the larger folds in the Jurassic Arapien Shale, and the trend of fold axes in the Arapien Shale indicate an eastward direction of movement for the upper plate of the Nebo Overthrust along a N.60-70" E. line. Minimum displacement is considered to be seven miles based on the occurrence of newly discovered fenstern containing critical stratigraphic units which are located north of the previously mapped position of the Nebo Overthrust.

Formations within the' mapped area attest to at least four compressive phases and two episodes of normal faulting, and probably several more. as a consequence of the Cedar Hills, Laramide, and Basin and Range deformations.

CONTENTS

TEXT Indianola Group ........................ 70 ................ Page Price River Formation 71

Introduction ........................................ 56 Tertiary System ................................ 72 Previous' Work ................................ 56 Golden's Ranch Formation ........ 72 Present Work ................................ 56 Tertiarv-Ouaternarv Svstems f ?) .... 73

Acknowledgments ................................ 58 ........................................ Stratigraphy 58

General Statement ............................ 58 .... Pennsylvanian-Permian Systems 58

.................... Oquirrh Formation 58 Permian System ................................ 60

Kirkman Limestone .................... 60 Diamond Creek Sandstone ........ 60 Park City and Phosphoria

Formations ................................ 61 Grandeur Member ........................ 61 Meade Peak Phosphatic

Shale Tongue ............................ 62 Franson Member ........................ 63

Triassic System ................................ 63 Woodside Shale ............................ 63 Thaynes Limestone .................... 64 Ankareh Formation .................... 64

. , Salt 'creek ~an~ lomera t e ............

............................. Quaternary System

............................ Old Alluvium ........................ Young Alluvium

Igneous Rocks .................................... ................................................ Structure

Folds ................................................ ............................ Nebo anticline

Folds in the Arapien Shale ........ ................................ Other Folds

Thrust Faults .................................... ........................ Nebo Overthrust

Foote's Canyon Thrust ................ Thrust Faults in the

Arapien Shale ........................ Nature, Direction, and Displace-

ment of Thrust Faults ............ ................................ Normal Faults

............................ Wasatch Fault Jurassic System ................................ 66 Cow Hollow Fault .................... 82

Nugget Sandstone ........................ 66 Transverse Normal Faults ........ 83 Arapien Shale ............................ 67 Normal Faults in the

Cretaceous Svstem ............................ 70 Ara~ ien Shale ........................ 83 - 'A thesis submitted to the Faculty of the Department of Geology, Brigham Young University, in partial fulfillment of the requirements for the degree Master of Science.

B. ALLEN BLACK

CONTENTS

Tectonism ......................................... 83 Nebo Overthrust relative to General Statement ............................ 83 other thrust faults In Utah ........ 57

........................ Cedar Hills Orogeny 83 2. Generalized stratigraphic ............................ Laram~de Orogeny 84 column ........................................ 59

Montana Phase ............................ 84 .... Paleocene Phase 85 3. Correlation of Arapien Shale 68 ............................

Eocene Phase ................................ 85 Basin and Range Deformation ........ 86 plates ........................ following page 80

Summary and Conclusions 87 1. Nebo Overthrust .................... References Cited 88 2. Thrust Faults Nebo Area

................................ 3. Folded Arap~en Shale ILLUSTRATIONS 4. Faulted ~ r & i e n Shale

figure page 5. Geologic Map of Mount Nebo- 1. Location of thesis area and Salt Creek Vicinity ............ in back

INTRODUCTION

This report concerns details of two conspicuous structural elements of the Wasatch Mountains east and northeast of Nephi, Utah: the overturned Nebo anticline and the Nebo Overthrust.

The Southern Wasatch Mountains in the vicinity of Mount Nebo and Salt Creek was mapped in detail with the primary objective of determining the nature, direction, and amount of displacement of the Nebo Overthrust.

Study of the stratigraphic units -resulted in more detailed subdivision than was possible by Eardley's (1933a; 1934) initial work or by Hintze's (1962) photogeologic interpretation. Mapped tripartite subdivision of the Permian Park City and Phosphoria Formations consists of the Grandeur and Franson Members of the Park City Formation a,nd the intervening Meade Peak Phos- phatic Shale Tongue of the Phosphoria Formation. Threefold divisions in the Thaynes Limestone and Ankareh Formation were also recognized but not mapped.

The mapped area is at the intersection of the Basin and Range, Middle Rocky Mountains, and Colorado Plateau physiogra hic provinces. It includes approximately 50 square miles immediately east a,n i northeast of Nephi, Juab County, Utah, and comprises parts of T. 12 and 13 S., R. 1 and 2 E. on the Nephi, Santaquin Peak, and Moroni quadrangles.

The area is accessible by numerous dirt roads and trails which leave U.S. Highway 91, State Highway 11, and the Nebo Loop Road (Text-fig. 1 ) .

Previous Work

The first general geologic investigations in the Southern Wasatch Mountains were by various directors of the early Territorial and Fortieth Parallel Survey. Loughlin (1 91 3) was the first to measure sections and map, in a reconnaissance fashion, the Nebo-Dry Mountain area, and it was he who f~ r s t noted thrusting in the Southern Wasatch Mountains, though he was not fully convinced of their overthrust character (Loughlin, 191 3, p. 449).

Eardley (1933a; 1933b; 1934) was the first person to study the Southern Wasatch Mountains in other than reconnaissance fashion. He mapped approxi- mately 240 square miles between Salt Creek near Nephi and the northern end of Dry Mountain near Santaquin. Spieker's (1946) regional stratigraphic report is also pertinent to the present investigation.

N E B 0 OVERTHRUST

L

4 Bannock Thrust

) Raft River Mtns

U T A H j

%den .& 0 2 0 40 60 80 Pi lot Range

Ogden 0 Willard Miles

Thrus B

Salt Lake City

1 Uinta Mountains - Deer Creek-Charleston Thrust

4 Gold Hill prove! 4 Strawberry Thrust

Sheep Rock Mtn 4 Santaquin Thruat

Thrust

Needle

y Wahwah Range Thrust

8 Cedar City

S . Beaver Dam

TEXT-FIGURE 1.-Index map showing location of thesis area relative to other thrust faults in Utah.

(1937; 1951) mapped the Cedar Hills to the east, contiguous to the present area.

More recently Johnson (1959) mapped 44 square miles in the Mount Nebo area, the southern half of which was remapped in the present investigation.

Present Work

Mapping was initiated June 15, 1964, and proceeded continuot~sly until September 18, 1964. Intermittent work was also done during May, June, July, and August of 1965.

5 8 B. ALLEN BLACK

Mapping was done on photo enlargements having a scale of approximately 1:10,000. Minor structures in the Arapien Shale were mapped in an attempt to rclate them to the Nebo anticline and Nebo Overthrust. Stratigraphic termi- nology is that currently being used elsewhere in the Wasatch Mountains.

ACKNOWLEDGMENTS

The writer expresses appreciation to advisory committee members, Drs. L. F. Hintze and H. J. Bissell, both of whom offered valuable assistance in solving structural and stratigraphic problems. Dr. Hintze first suggested the problem and allocated funds for the study from a National Science Foundation grant which he received to study the structure of the Southern Wasatch Mountains. Drs. L. F. Hintze and J. Keith Rigby criticized the manuscript and made suggestions con- cerning presentation of data.

Appreciation is also extended to my wife for her sup rt and continual encouragement and to my parents who also provided fun s to complete the project.

g. STRATIGRAPHY General Statement

From 24,000 feet to 32,000 feet, depending on thickness of the Oquirrh Formation and Arapien Shale, of Paleozoic, Mesozoic and Cenozoic rocks are exposed in the Southern Wasatch Mountains. Paleozoic strata are mainly marine limestone and sandstone with subordinate amounts of marine shale. Mesozoic rocks are predominantly red siltstone, sandstone, shale, and conglomerate with some gray marine limestone. Cenozoic strata consist of conglomerate, sandstone, water-deposited volcanics, and stream gravel (Text-fig. 2) .

Pennsylvanian-Permian Systems Oquirrh Formation

Mount Nebo and the High South Ridge, which comprise the northwest quarter of the mapped area, consist of Oquirrh rocks (Plate 5) . The formation occurs in the inverted eastern limb of the Nebo anticline and dips 20° to 60° north and northwest.

Oquirrh strata here consist of thin to massively bedded, fossiliferous, gray and brownish gray limestone and intercalated brownish and tan calcareous orthoquartzite and sandstone. Limestone units are mainly arenaceous, bioclastic, and crinoidal, though near the top of the formation some porous, case-hardened, hydrocarbon-smelling, dolomitic limestone occurs which is quite similar to that in the overlying Kirkman Limestone. Minor units of black, arenaceous and silty, laminated shale occur as interbeds. Limestone, sandstone, and orthoquartzite are estimated to be present in approximately equal amounts. The formation as a whole is lenticularly bedded. Along the trace of the N e b Overthrust where Oquirrh rocks are in contact with Nugget Sandstone, the former are highly brecciated and pulverized. An extensive breccia zone in Oquirrh rocks at the mouth of Willow Creek in interpreted to be the result of proximity to the normal Wasatch fault-Nebo Overthrust intersection, the latter not far below the present surface.

Johnson (1959, p. 45) indicated the Oquirrh Formation is in excess of 11,500 feet in the Mount Nebo area, and 18 miles to the north in the Dry Mountain-Loafer Mountain vicinity, Metter (1955, p. 90) measured a partial

Formation

TEXT-FIGURE 2.-Generalized Stratigraphic Section.

Price River Formation

section of 7000 feet and expressed the opinion that less than 12,000 feet is present in that area.

Welsh and James (1961, p. 3-11) and Bissell (1962, p. 26-33) indicated an Early Pennsylvanian to Early Permian age for the Oquirrh Formation. John- son (1959, p. 10) stated that locally only Deslnoinesiatl through Wolfcampian Oquirrh rocks are present.

60 B. ALLEN BLACK

The Oquirrh-Kirkman contact is gradational and was drawn at the top of an orthoquartzite sequence which is overlain by light gray, commonly brecciated, case-hardened cliff-forming limestone and dolomitic limestone.

Permian System Kirkrnan Limestone

Kirkman Limestone crops out discontinuously from Round Top Hill, northwestern corner of Sec. 26, T . 12 S., R. 1 E., to the North Fork o € Salt Creek, where it passes beneath the Price River Formation in a classic angular un- conformity (Plate 5 ) . Best and most continuous exposures are located on the North Fork of Salt Creek and at the head of Red Canyon. The formation stands as a conspicuous light gray cliff from the North Fork of Salt Creek to Andrew's Canyon, but elsewhere it tends to be more subdued.

Kirkrnan Limestone in the mapped area is characteristically light to medium gray, thin to thick bedded, cherty limestone and dolomitic limestone. The lower part is characteristically brecciated, case-hardened, and emits a hydrocarbon odor when broken, but the upper part is generally thinner bedded, conspicuously more cherty, and tends to form a slope. The middle portion is very cherty and contains abundant fusulinids. Laminations were noted at only one outcrop on the North Fork of Salt Creek.

Although this lithology is not consistent with thc type Kirkman, the writer believes that these rocks are the lateral equivalent of the Kirkman Lime- stone on the basis of similar stratigraphic position, similar overlying and under- lying formations, and the presence of Wolfcampan age fusulinids. Bissell (1962, p. 34) indicated that as the Kirkman Limestone is-traced south and west from the type locality it becomes progressively more dolomitic.

The writer measured a complete Kirkman section 368 feet thick at the head of Red Canyon, and Johnson (1959, p. 34) obtained a thickness of 300 feet in the same vicinity.

Fusulinids, collected from the fossiliferous middle cherty portion of the Kirkman Limestone, were identified by Bissell (oral communication) as Pseudoschwageri~~a udde)zi (Beale and Kniker), Medial Wolfcampian age. Johnson (1959, p. 10-11) identified robust Wolfcampian Tr.ilicites sp. and Schwagerina sp. from the formation. Bissell (1962, p. 34) indicated that at all places where he has studied the Kirkman Limestone it contained diagnostic Medial to Late Wolfcampian fusulinids.

The Kirkman-Diamond Creek contact seems fairly sharp and commonly coincides with an abrupt break in both lithology and topography. Thin bedded, light gray, cherty and arenaceous limestone occurs stratigraphically below and gray to buff, cross-bedded, friable sandstone above the contact.

D~amond Creek Sandstone Diamond Creek Sandstone commonly forms a float covered slope between

the overlying Grandeur Member of the Park City Formation and the underlying Kirkman Limestone. The best outcrops occur or1 the North Fork of Salt Creek, near the head of Andrew's Canyon, and at the head of Red Canyon. The forma- tion crops out almost continuously from Round Top Hill to the North Fork of Salt Creek but is truncated by the Nebo Overthrust in the former area and passes beneath the Price River Formation in the latter area (Plate 5 ) .

The Diamond Creek Sandstone is a gray to buff or locally red, friable to compact, in part calcareous t o quartzitic, highly cross-bedded sandstone in the mapped area.

N E B 0 OVERTHRUST 61

At the head of Red Canyon 334 feet of Diamond Creek sandstones were measured, and in the same vicinity Johnson (1959, p. 12) obtained a thickness of 395 feet.

Since no fossils have been obtained from the Diamond Creek Sandstone, it is dated as probably Leonardian on the basis of stratigraphic position.

The Diamond Creek-Grandeur Member contact is gray to buff, cross-bedded sandstones below and thin to medium bedded, gray or pinkish, arenaceous and cherty limestone above the contact as observed near the headwaters of Red Canyon, Andrew's Canyon, and the North Fork of Salt Creek. On the North Fork of Salt Creek a transition zone of brecciated pinkish sandstone, calcareous sandstone, and arenaceous limestone occurs at the contact and may be inter- preted as either locally reworked sediments or local brecciation due to bedding plane movement.

Park City and Phosphoria Formations The Park City Formation was proposed by Boutwell (1907, p. 443) for

intercalated limestone, sandstone, and orthoquartzite between the Weber Forma- tion and the Woodside Shale in Cottonwood Canyon, southeast of Salt Lake City, Utah. Gale and Richards (1910, p. 460) recognized a phosphatic shale member within the Park City Formation in its type area, and shortly there- after, it was shown to be continuous with the phosphatic shale member of the Phosphoria Formation, named by Richards and Mansfield (1912, p. 684-689) for dark chert, phosphatic and carbonaceous mudstone, phosphorite, cherty mudstone, and minor amounts of dark carbonaceous rock occurring in Phos- phoria Gulch, Bear Lake County, Idaho. Nevertheless, in most of Utah the phos hatic shale continues to be called the middle member or middle shale mem le r of the Park City Formation (McKelvey et al, 1956, p. 2840). Mc- Kelvey et d (1956; 1959) discussed the stratigraphic and nomenclatorial prob- lems associated with the Park City and Phosphoria Formations and concluded (1959, p. 9 ) :

"Eleven subdivisions of these formations are recognized as members. Members of the Park City formation are designated the Grandeur member, the Franson member, and the Ervay carbonate rock member. Those belonging to the Phosphoria formation are the Meade Peak phos- phatic shale member (the phosphatic shale member of Richards and Mansfield), the lower chert member, the Red chert member, the cherty shale member, and the Tosi chert member. . . ."

Two such members of the Park City Formation and one such tongue of the Phosphoria Formation were recognized and mapped in the Mount Nebo area, and in ascending order they are: the Grandeur Member (Park City Formation), the M a d e Peake Phosphatic Shale Tongue (Phosphoria Formation), and the Franson Member (Park City Formation). These three units occur in the upper plate of the Nebo Overthrust or other associated thrust faults within the mapped area.

Grandeur Illember.-Grandeur rocks crop out extensively throughout the present area, but the best and most continuous exposures are present on the North Fork of Salt Creek, in Andrew's Canyon, in Quaking Asp Canyon, and at the head of Red Canyon. Outcrops typically form prominent strike ledges between slopes of Diamond Creek Sandstone and Meade Peak Phosphatic Shale Tongue.

Pinkish to medium gray, thin to thick bedded, in part silty and arenaceous, fossiliferous limestone typifies the Grandeur Member here. Black and white or

62 B. ALLEN BLACK

cream colored cherty zones are common throughout the unit, especially im- mediately above the base and below the uppermost massive limestone bed. The top of the member is characterized by an exceptionally fossiliferous, 35 foot thick, blue-gray, brachiopod limestone bed which serves as an important reference datum in structurally complex areas.

The writer measured 508 feet of Grandeur Member at the head of Red Canyon. Of Johnson's (1959, p. 44) Permian section, which was measured in the same vicinity, the writer attributes approximately 417 feet to the unit.

McKelvy et al. (1959, p. 36) indicated that Baker and Williams (1940) found a fauna in the Grandeur Member in the Hobble Creek area which has Kaibab affinities and that this fauna has been found elsewhere in the member as well. They inferred a Leonardian age for the unit but were still working on the fossils at the time of publication. The writer tentatively assigns a Leonardian age to the Grandeur Member of the Mount Nebo area and correlates it with the type Grandeur on the basis of similar lithology and stratigraphic position.

Contact with the overlying Meade Peak Phosphatic Shale Tongue of the Phosphoria Formation is sharp and was drawn at the top of a persistent massive, 35 foot thick, blue-gray, extremely fossiliferous limestone. An eighteen inch thick oolitic phosphorite bed and a sequence of brownish black cherty lime- stone of the Meade Peak Phosphatic Shale Tongue stratigraphically overlie the massive limestone bed. The contact also coincides with a break in topography, for Meade Peak rocks tend to form a slope whereas Grandeur rocks are typically ledgy.

Meade Peak Phorphratic Shale Tongue.-The Meade Peak Phosphatic Shale Tongue is best exposed on the North Fork of Salt Creek, in Andrew's Canyon, in Quaking Asp Canyon, and near the head waters of Red Canyon. It charac- teristically forms a rubble covered slope between the Grandeur and Franson Members of the Park City Formation.

By far the most common and diagnostic rock in the Meade Peak Tongue is a brownish black, cherty limestone which forms a monotonous lithologic interval. Similar rocks also occur in both the Grandeur and Franson Members, but those in the Meade Peak have interbedded phosphorite beds and very thin zones of black paper shales. Only three phosphorite beds were noted, and of these, only the one immediately above the massive uppermost limestone bed of the Grandeur Member is of any importance. It is eighteen inches thick on the North Fork of Salt Creek and is apparently continuous throughout the entire area. The other phosphorite beds vary from four to six inches thick and occur in the middle part of the Meade Peak Tongue.

At the head of Red Canyon, M a d e Peak strata total 162 feet in thickness, but considerable thinning was noted due to thrusting. From Johnson's (1959, p. 44) description of the Park City Formation, it is ossible to assign approxi- mately 184 feet of his section to the Meade Peake '&ngue. Baker et a1 (1949, p. 1189) reported a thickness of 268 feet for the "middle unit of rocks cor- related with the Park City formation" on the North Fork of Salt Creek, but no phosphorite was observed, perhaps because the area is badly faulted.

The Meade Peak phosphatic Shale Tongue occurs stratigraphically above the Leonardian Grandeur Member of the Park City Formation. McKelvey el a1 (1959, p. 39) indicated that the tongue contains fossils which may be as young as Wordian. Consequently, the unit is tentatively assigned a Leonardian to Wordian age in the Mount Nebo area.

N E B 0 OVERTHRUST 63

The Meade Peak-Franson contact is sharp and was placed at the first occurrence of light gray, dense, medium bedded limestone and dolomitic lime- stone of the Franson Member of the Park City Formation. These are underlain by the brownish black, cherty limestones of the Meade Peak.

Fratzson Member.-Excellent exposures of the Franson Member occur as an almost continuous band from Round Top Hill, where the member has been truncated by the Nebo Overthrust on the west, northeast to the North Fork of Salt Creek, where the member passes beneath the Price River Formation in a striking angular unconformity (Plate 5 ) . The best outcrops are located on the North Fork of Salt Creek, in Andrew's Canyon, in Quaking Asp Canyon, and in Red Canyon. Because it is overturned throughout most of its extent, the Franson Member forms the topographically lowermost ledgy outcrops of the Park City Formation.

A series of medium to light gray, medium to thick bedded, fossiliferous and cherty, in part arenaceous, silty, and argillaceous limestone, dolomitic limestone, and dolomite is regarded as the Franson Member in the map area. This unit contains less chert, weathers lighter, and is conspicuously more dolomitic than the Grandeur Member. The uppermost 30 feet of the Franson Member is com- posed of light gray-weathering limestone which contains abundant large bryozoans.

Franson beds aggregate 432 feet thick in Red Canyon, but thrusting here has resulted in thinning of the member, as it probably has through the entire Permian section. Baker et al ( 1949, p. 1189) measured 615 feet "for the upper member of the Park City formation" on the North Fork of Salt Creek. Muessig (1951a, p. 62) did not subdivide the Park City Formation on Long Ridge but does indicate a total thickness of 2000 feet.

The age of the Franson Member is unknown, but a tentative Leonardian tc Wordian age is postulated by the present writer for these rocks in the mapped area on the basis of the discussion by McKelvey et a1 (1959, p. 39) concerning the age of the Mead Peak Tongue which stratigraphically underlies the Franson.

The Franson-Woodside contact is fairly sharp though it is poorly exposed. It consists of the light gray, bryozoan limestones of the Franson Member below and the red and greenish shales and siltstones of the Woodside Shale above. Not uncommonly this contact is characterized by thrusting which has resulted in discordant attitudes and a gouge zone, as for example north and northeast of Ree's Flat (Plate 5 ) .

Triasic System Woodside Shale

Woodside Shale characteristically forms a float and vegetation covered slope between the Franson Member and the Thaynes Limestone on all the spurs along the east side of Mount Nebo. Good exposures are few, but the best and most continuous ones occur in Andrew's Canyon, on the ridge between Andrew's and Salt Spring Canyon, and at the head of Foote's Canyon. Less well exposed sections occur in Bear Hollow and northeast of Ree's Flat.

The Woodside Shale is red shale with subordinate red and greenish siltstone and brownish red sandstone. The sandstone is fine textured and highly cross- bedded on a small-scale, but these features, along with the brownish red color, serve to distinguish it from any other sandstone in the mapped area. Approxi- mately 100 feet of this sandstone occurs below the Thaynes Limestone through- out the entire area.

64 B. ALLEN BLACK

On the spur immediately south of Foote's Canyon, a section of Woodside Shale 559 feet thick was measured. The formation varies in thickness due to thrusting, and probably nearly 1000 feet of Woodside Shale is exposed in Andrew's Canyon.

Reeside et a1 (1957, chart) assigned an Early Triassic age to the Woodside Shale.

The Thaynes-Woodside contact constitutes a fairly sharp lithologic and topographic break and was observed at the head of Andrew's Canyon, on the North Fork of Salt Creek, in Foote's Canyon, on Miner's Ridge, and in Red Canyon. Peculiarly, at all places where the contact was actually seen, the lowest Thaynes limestones are characterized by very small but fairly abundant bright green seams. Brownish red Woodside shales, siltstones, and sandstones occur below and medium gray, medium bedded, arenaceous Thaynes limestones occur above this contact.

Thavnes Limestone In the Mount Nebo area the Thaynes Limestone forms excellent outcrops

extending from Ree's Flat to the North Fork of Salt Creek. Partial sections also crop out on Miner's Ridge, in the area immediately west of Round Top Hill and between Foote's and Maple Spring Canyons. At the latter three locations the formation is involved in extensive thrusting (Plate 5 ) .

Two arenaceous and calcareous units, separated by a red shale and siltstone sequence, occur in the mapped area just as in the type area. The lower unit is characterized by reddish brown sandstones, in part calcareous, with lesser amounts of interbedded gray limestone and greenish siltstone and shale. The upper unit is considerably more calcareous, composed dominantly of arenaceous, gray limestone with some interbedded buff and brownish sandstone. The inter- vening red shale and siltstone is similar to parts of the Woodside Shale under the Thaynes Limestone.

Thaynes strata are 1350 feet thick on the south side of Foote's Canyon. Johnson (1959, p. 43) measured a partial section of 300 feet on Miner's Ridge where the formation is truncated by the Nebo Overthrust, and Eardley (1933a, p. 326) estimated 500 to 1000 feet of Thaynes beds present within the Mount Nebo area.

Kummel (1954, p. 171) stated the Thaynes Limestone "is the most fos- siliferous formation of Triassic age in the Middle Rocky Mountains." Limestone beds composed of abundant fossil fragments are not uncommon in the unit. Johnson (1959, p. 17) reported finding Pentacr.inur zuhitei and Meehoccras sp., the latter a diagnostic Lower Triassic fossil, within the mapped area. The Thaynes Limestone is Early Triassic age in the Mount Neb0 area and is cor- related with the type Thaynes on the basis of similar fauna, lithology, and strati- graphic position. -

The ~ h a ~ n e s - ~ n k a r e h contact is fairly sharp, though it is poorly exposed, and was observed in Andrew's Canyon, in McCune Canyon, in Foote's Canyon, and immediately west of Round Top Hill. It coincides with a lithologic and topographic break marked by gray limestone and brownish sandstone below and red shale and siltstone of the Ankareh Formation above.

Ankareh Formation Boutwell (1907, p. 452; 1912, p. 58) proposed the Ankareh Formation

for a red sandy sha!e on Ankareh Ridge in the Park City District, Utah. As

NEB0 OVERTHRUST

originally defined, the Ankareh Formation included all rocks between the Thaynes and Twin Creek Limestones. Later Boutwell (1912, p. 452; 1933, p. 73-74) restricted the formation to strata between the Thaynes Limestone and the Nugget Sandstone. At the same time, the earlier assigned age of Permian for the Woodside, Thaynes, and Ankareh was changed to Triassic. The Ankash Formation, a used In th~s~rc,1,u~eha!l beds between the Thaynes Lime- stone and the '~~ggett~~~~~~ad;~&~~~l (191 2, p. 45 2 T l B 3 , b. 73-74).

~ n k a r e h rocks are commonly poorly exposed in the Mount Nebo area. The most continuous outcrops exist in Foote's Canyon, on the saddle between Foote's C a q o n and McCune Canyon, in Andrew's Canyon, and in the area north of the North Fork of Salt Creek.

The Ankareh Formation comprises a tripartite lithic sequence in the mapped area. The lower Dart consists of red shale with lesser amounts of red and

1

greenish gray siltstone with several dull red, massively bedded and cross- bedded sandstone beds near the top of the lower portion. One such sandstone, approximately 30 feet thick, is well exposed in an old quarry in Andrew's Canyon and also along the north side of Foote's Canyon. The middle Ankareh Formation consists of coarse sandstone and conglomerate, both of which contain clots of dark red shale. The conglomerate has white quartzite, dark gray chert, and red sandstone pebbles or cobbles embedded In a sandy or gritty matrix. Texture and thickness varies from one exposure to the next. The upper portion of the formation is composed of poorly exposed maroon, red, lavender, purplish, and pale green shale beds and several overlying buff or purplish white, quartzitic sandstone beds, the latter mark the top of the formation wherever a complete section is present. In ascending order these subdivisions would possibly corres- pond to the Ankareh, Gartra, and Stanaker Formations of Thomas and Krueger (1946) in the western Uinta and Central Wasatch Mountains, or else the upper Moenkopi, Shinarump, and Chinle Formations of the Colorado Plateau region.

A thickness of 934 feet was obtained for the Ankareh Formation along the north side of Foote's Canyon. Johnson (1959, p. 18) measured approximately 400 feet near the mouth of Red Canyon, a structurally complex area. Eardley (1933a, p. 329) obtained a thickness of 1500 feet for the Ankareh Formation on the North Fork of Salt Creek, but he included part or all the Nugget Sand- stone in the unit, probably as a result of using Boutwell's (1907, p. 452) original definition of the Ankareh Formation.

Exact age of the Ankareh Formation is not known, but since the lower contact with the Thaynes Limestone is apparently gradational and because the grit and conglomerate in the middle part of the formation are interpreted by some geologists as indicating an hiatus, that portion between the underlying Thaynes Limestone and the base of the grit or conglomerate is assigned to the Upper Lower Triassic, and that portion between the base of the grit or con- glomerate and the overlying Nugget Sandstone is designated Upper Triassic (Reeside et al, 1957, chart). Since no better evidence is available in the Mount Nebo area for dating the Ankareh Formation, the writer follows the usage of Reeside.

The Ankareh-Nugget contact is somewhat arbitrary and was selected to coincide with the top of a sequence of coarse grained, purplish white sandstone beds in the Ankareh which have counterparts below but not above the contact. Overlying these purplish white sandstones is a thick sequence of massively cross-bedded, salmon colored sandstone which may be locally white or grayish

66 B. ALLEN BLACK

white. Commonly this contact coincides with a slight topographic depression along most of its extent.

Jurassic System Nugget Sandstone

Bold conspicuous outcro s characterize the Nugget Sandstone in the Mount B Nebo area. Massive rounde and knobby outcrops extend from Foote's Canyon to the North Fork of Salt Creek where the formation passes beneath the Price River Formation in an impressive angular unconformity (Plate 5 ) . Nugget beds also crop out extensively in the Red Canyon vicinity and in the fenster along the western margin of Mount Nebo where they are involved in the Nebo Overthrust (Plate 5 ) . Well exposed sections of Nugget Sandstone occur at these localities, and the unit serves as an excellent reference datum in the structural analysis of the region. This formation has been cut out by thrusting between Red Canyon and Foote's Canyon.

Two distinct facies of Nugget Sandstone occur in the mapped area, one above and the other below the N e b Overthrust. A thick partial section of friable to compact, porous, medium grained, moderately well bedded to massive- ly cross-bedded sandstone occurs below the Nebo Overthrust along the west side of Mount N e b (Plate 5 ) . It is dominantly buff colored except for the lowermost exposures which are red, and in all respects, this facies resembles the Nugget Sandstone at Thistle, Utah, which is similarly colored. All other outcrops are above the Nebo Overthrust or occur as slices along the thrust fault and consist of moderately well bedded to massively cross-bedded, porous, friable to compact, salmon colored or locally white sandstone. The latter facies fits the description of the Nugget Sandstone by Muessig (1951a, p. 66) and the observations made by the writer on Long Ridge west of Mount Nebo.

Nugget beds aggregate only 258 feet thick along the north side of Foote's Canyon, but the unit is known to be thicker to the north and southwest. If the difference between Eardley's (1933a, p. 329) thickness for the Ankareh For- mation and the writer's figure for the same unit is considered, a thickness of approximately 600 feet is obtained. This value is more realistic for the Nugget Sandstone in the vicinity of Mount Nebo, but it too is probably a minimum value.

Considerable doubt still exists concerning the age of the unfossiliferous Nugget Sandstone. Imlay (1952, chart) assigned an Early Jurassic age to the formation, but McKee et al (1959, p. 22-23) believe the Triassic-Jurassic boundary lies within the unit in southwestern Wyoming. Because no lithologic cr paleontologic data are known to substantiate their viewpoint, however, they also assigned the formation to the Lower Jurassic and drew the Triassic-Jurassic boundary at the base of the sandstone, realizing that Upper Triassic rocks may be included in the lower part of the formation. The writer has no new data to offer with respect to dating the Nugget Sandstone. - - -

The Nugget-Arapien contact is sharp and well exposed along most of jis trace. Massively cross-bedded, buff, white, or salmon colored sandstone below and brownish gray or purplish, thin to thick bedded, fossiliferous and oolitic limestone above typify the contact. The basal Arapien Shale (unit one) is comonly highly fractured because of proxim~ty to the Nebo Overthrust and associated thrust faults. A bright red shale and silrstone zone a few feet thick commonly coincides with the contact in the upper plate of the Nebo Overthrust, but in the lower plate, oolitic Arapien limestones rest directly on buff or gray

NEB0 OVERTHRUST 67

Nugget Sandstone. Except in the lower plate, the contact is vertical or over- turned and is well exposed in Red Canyon, Foote's Canyon, and the North Fork of Salt Creek.

Arapien Shale Spieker (1946, p. 123-125) originally defined the Arapien Shale for a

series of red to gray shale, fine grained siltstone, salt- and gypsum-bearing in part, in Arapien Valley, southeast of Gunnison, Utah. Initially Spieker (1946, p. 123-125) designated a lower Twelve Mile Canyon Member and an upper Twist Gulch Member. Shortly after, Hardy (1952, p. 16) restricted the Arapien Shale to the Twelve Mile Canyon Member. This latter usage is adopted in the present paper.

Spieker (1946, p. 124) recognized five distinct lithologic types in the original Arapien Shale:

1. Gray thin bedded limestone. 2. Light-gray siltstone and shale with occasional beds of ripple-marked

sandstone. 3. Gray gypsiferous shale with red blotches. 4. Compact red salt-bearing shale. 5 . Thin bedded red siltstone and shale.

Spieker included types one through four in the Twelvemile Canyon Member, now the restricted Arapien Shale (Hardy, 1952, p. 16), and designated type five as the Twist Gulch Member, now referred to as the Twist Gulch Forma- tion. These lithologic types of Spieker are not stratigraphic units but rather rock types characteristic of the Twelvemile Canyon Member and occur at various stratigraphic intervals within it.

Subsequent work by Hardy (1952, p. 15-16) resulted in recognition of five informal stratigra hic units in the restricted Arapien Shale. These are listed below, with A 01 e!' est and E youngest:

E. Brick-red silty shale, locally salt-bearing. D. Alternate layers of bluish gray and red gypsiferous shale with blotched appear-

ance. C. Bluish gray calcareous shale with gray thin bedded calcareous sandstone. 13. Bluish gray and red gypsiferous shale. Blotched appearance similar to unit D.

Red gypsiferous shale in upper part. A. Gray shale, gray thin bedded limestone which weathers brown, red shale, gypsum

in thin lenticular beds; or gray thin bedded argillaceous limestone with massive lenticular beds of gypsum.

Hardy's informal stratigraphic units are recognizable in the Nebo area and an additional unit may be present between units D and E. Relationships between the lithologic types of Spieker, the informal stratigraphic units of Hardy, and the informal stratigraphic units recognized by the writer are summarized in Text-figure 3.

Excellent exDosures of the Ara~ ien Shale occur throughout the southern I (7

and eastern ortion of the mapped grea, as well as on the west side of Mount Nebo and f orm a characteristically subdued badland topography. Extensive deformation obscures normal stratigraphic relationships within the formation, and consequently, distribution and lithologic nature of individual units will be discussed together.

68 B. ALLEN BLACK

TEXT-FIGURE 3.-Correlation of Arapien Shale at Mount Nebo-Salt Creek with that of the Wasatch Plateau and Sevier Valley.

Unit one is best exposed above the Nugget Sandstone and below the Nebo Ovetthrust from Gardner's Canyon to Birch Creek, along the entire extent of Miner's Ridge, at the mouth of Salt Creek Canyon, and on the North Fork of Salt Creek below the overturned Nugget Sandstone. It is an unknown thick- ness of grayish brown to urplish, thin to thick bedded, fossiliferous and oolitic limestone; thin to me!ium bedded, biwlastic limestone; very thin bedded

A

R . A

P

I

E

N

S

H

A

L

E

S p l e k e r (1946)

Rock es

4

1,2

3

1,2

3

1.3

H a r d y (1952)

U n l t s

E

n o t - e p o r t e d

D

C

B

A

U n i t

6

5

4

3

2

I

THIS REPORT

D e s c r i p t l on

Red compact s h a l e w i t h seme r e d s l l t s t s n e ; l o c a l l y s a l t and gypsum b e a r i n g .

Gray l i m e s t o n e , t h i n bedded and laminated; g r a y s h a l e ; g r a n g r e e n l s h - g r a y , b u f f and d a r k brown sands tone , cross-bedded and r l p p l e marked; l e n s e s o f d a r k brown p e b b l e cong lomera te ; f o s s i l l f e r o u s .

Red and g r a y s h a l e w i t h l e n t i c u l a r and i r r e g u l a r l y b l o t c h e d r e d g y p s i f e r o u s zones.

Gray I l m e s t o n e , t h l n bedded, lamina ted , a r g i l l a c e o u s , w i t h s p l l n t e r y f r a c t u r e ; g r a y s h a l e ; m i n o r amounts o f r e d and g r e e n mudstone; Du f f Sand8tone, r i p p l e marked and cross-bedded; g r a y - b u f f s i l t s t o n e , h i g h l y r i p p l e d and lamina ted ; f o s s l l l f e r o u s .

Red and g r a y s h a l e w i t h l e n s e s o f h i g h l y deformed g y p s l f e r o u s zones w h i c h a r e i r r e g u l a r l y b l o t c h e d red; s h a l e and gypsum b r e c c i a common; r e d s h a l e a t t h e t o p of t h i s u n i t .

Gray-brown, p u r p l i s h l i m e s t o n e ; t h i n t o t h i c k bedded, o o l i t i c , a r g i l l a c e o u s , f o s s i l i f e r o u s ; I n t e r b e d d e d g r a y s h a l e and some l e n t i c u l a r g y p s i f e r o u s zones w l t i a t l e a s t one mass ive w o r k a b l e d e p o s i t o f gypsum a p p r o x i m a t e l y 80' t h l c k .

NEB0 OVERTHRUST 69

and in part laminated, argillaceous limestone which exhibits a characteristic splintery fracture; and subordinate amounts of interbedded red and gray shale and lenticular to massive gypsum beds. These lithologies occur in approximately this same order h o m the base upwards in the field.

Unit two is we!] exposed in the area between Juab Valley on the west, lower Quaking Asp Canyon in the north, Ree's Flat on the east, and Salt Creek Canyon on the south, as well as on the south side of State Highway 11 in the vicinity of the mouth of Salt Creek Canyon. An unknown thickness of de- formed red and gray shale with interbedded lenticular and pod-shaped gyps- iferous zones, locally a clay and gypsum breccia which is conspicuously and irregularly red blotched, constitutes unit two. This unit locally provided the lubricant for the Nebo Overthrust and associated thrust faults.

Unit three is best exposed immediately east, west, and south of the Ree's Flat Road. It is composed of interbedded, very thin bedded and laminated, argillaceous limestone which exhibits a characteristic splintery fracture; and gray calcareous shale with lesser amounts of gray to buff, ripple marked and cross-bedded, thin bedded sandstone, and very common finely rippled and laminated siltstone. A few lenticular beds of gypsum and red shale give rise to local red blotches.

Unit four is best seen on the hill immediately west of a point at which the Foote's Canyon Road leaves State Highway 11, as well as approximately half way up Salt Spring Canyon. Approximately 200 feet of interbedded lenticular and pod-shaped gypsiferous zones and red and gray shale comprise unit four. It is also conspicuously and irregularly red blotched and considerably deformed.

Unit five can be seen up Salt Spring Canyon above Unit four, and in most of the area immediately east and west of the Foote's Canyon Road, as well as in the vicinity of Rock Ridge Canyon. This unit is similar to unit three but lacks gypsiferous zones. Finely rippled and laminated siltstones are nearly absent, but coarser sandstone is more abundant. Sandstones are gray, greenish gray, and dark brown, locally conglomerate and contain reworked gray lime- stone fragments. Muscovite is conspicuous in the lighter colored sandstones. Rapid facies changes are common in both unit three and five, but particularly in the latter.

Unit six, the uppermost subdivision of the Arapien Shale, is well exposed on the north side of State Highway 11 near a locality at which the younger light colored volcanics overlap unit five, and also in the vicinity of Salt Spring Creek and the Red Creek-North Fork junction (Plate 5) . It consists of compact dull red shale, locally bearing salt and gypsum, along with minor amounts of dull red and buff siltstone and sandstone. A few beds of black bryozoan limestone and laminated shale with a strong hydrocarbon odor and some hydrocarbon residue were noted near the mouth of Salt Spring Creek.

A stratigraphic section of the Arapien Shale was not measured because of extensive deformation and lack of continuous exposures, especially in the gypsiferous portions of the formation. Eardley (1933a, p. 331) postulated 4200 to 11,000 feet of Arapien Shale present in the Mount Nebo area. Johnson (1959, p. 22) reported 8500 feet in the vicinity of Salt Creek, and Hardy (1952, p. 16) measured a partial section of Arapien Shale totaling 2700 feet in Chicken Creek Canyon east of Levan, Utah. Hardy (1952, p. 17) believes thicknesses expressed by Eardley are excessive, but does indicate the Arapien Shale is cer- tainly not less than 3000 feet thick. The writer considers the formation to be from 3000 to 5000 feet thick in the mapped area.

70 B. ALLEN BLACK

Ossicles of Pentacrinus a~teriscus and various pelecypods are the most commonly noted fossils in the Ara ien Shale, but several black limestone beds in unit six, the red salt- and gypsum- \ earing portion, contain abundant bryozoans. Imlay (1952, chart) assigned a tentative Medial to Early Late Jurassic age to the formation, as did McKee et a1 (1956, p. 5 ) , and the writer has n o basis to question this assignment. It is correlated without difficulty with the type Arapien Shale on the basis of similar lithology, stratigraphic position, and nearly continuous exposures between the mapped area and the type area.

N o Twist Gulch Formation was observed within the Mount Nebo area, but it may be present but covered by younger rocks. Thus the exposed contact between the Arapien Shale and all younger formations is unconformable, locally angular.

Cretaceous System Indianola Group

Indianola outcrops are widespread east and southeast of the area, though only the lower part occurs within the mapped area. These exposures are con- tiguous with those of the Cedar Hills to the east and the Gunnison Plateau to the south. A less extensive and disconnected outcrop of red conglomerate, sandstone, shale, and limestone occurs immediately east of Ree's Flat and is tentatively regarded as Indianola. These exposures are important in recon- struction of the geologic history of the region.

Shale, sandstone, algal limestone, and conglomerate make up the Indianola Group in the map ed area. The shale is bright red and weathers to produce a P subdued but color ul topography and is dominant in the lowermost exposures of the Indianola Group. Sandstone beds are dominantly buff, pinkish white, and gray, and are typically friable and coarse textured. They frequently grade laterally to grit and conglomerate, and because of their lighter color, give rise to light streaks in the bright red shale topography. Algal limestone beds are the least common and weather reddish and yellowish gray. Beds up to four feet thick were noted.

Sandstone with lesser amounts of limestone and conglomerate, makes up the middle ex osures of the Indianola Group within the mapped area. Conglomerate units are g uff, gray, or pinkish white and contain purplish, buff, red, maroon, and white quartzite pebbles or boulders, with lesser amounts of identifiable Cambrian through Pennsylvanian carbonate clasts. Quartzite fragments are com- monly more rounded, larger, and more prevalent and are embedded in a light colored coarse sandy matrix. Conglomerate, with subordinate amounts of sand- stone, is by far the most common lithology of upper exposures of the Indianola Group within the mapped area.

At least 1000 fee; of Indianola strata are present within the Mount Nebo area. Outcrops are continuous with those in the Cedar Hills to the east. Schoff (1951, p. 4 9 ) reported approximately 7000 feet for the group on the Gunnison Plateau to the south.

Age of the Indianola Group is still in question. Schoff (1951, p. 625-626) reported finding Coloradoan fossils in the marine portion of the group in the Cedar Hills, some 900 feet above the exposed base and 2300 feet below the top, and Hunt (1950, p. 52) found plant remains which were identified as Late Cretaceous age 4000 feet above the base of the group on the Gunnison Plateau. Indianola beds within the mapped area are stratigraphically below Schoff's marine portion a'nd Hunt's fossiliferous beds, and thus an Early to

N E B 0 OVERTHRUST 7 1

Medial Colorado Age is the youngest possible age that can be assigned to them. However, this does not exclude the possibility ot an Early Cretaceous or even Late Jurassic age for the lower undated portion of the Indianola Group.

The contact between Indianola strata and all younger formations within the mapped area is unconformable, locally angular. Lowermost Indianola Group is angularly overlain by Golden's Ranch Formation in the vicinity of the North Fork of Salt Creek. Hunt (1950, map) shows the Indianola Group over- lapping successively younger Arapien Shale and 'I'wist Gulch rocks from west to east along the northern margin of the Gunnison Plateau. This relationshi can be viewed from the junction of State Highway 1 I and the Nebo Loop Road: looking south at the Gunnison Plateau. In addition, if the outlier east of Ree's Flat has been correctly identified, it substantiates an angular unconformity between Indianola and Arapien strata because Indianola rocks rest with angular discordance across units four and five of the Arapien Shale. T h e Indianola- Price River contact is similarly a major regional angular unconformity (Spieker, 1946, p. 126; Schoff, 1951, p. 628; Hunt, 1950, map; Hardy and Zeller, 1953, p 1268; and Hardy, 1962, p. 57) .

Price River Formation Price River Formation, as used in this report, corresponds to the western

conglomerate facies of Spieker (1946, p. 130-132) and to rocks mapped as Price River Formation by Schoff (1951, p. 627-628) and Hunt (1950). Schoff (195 1, p. 627) described them as massive red conglomerate and dark red lenticular sandstone which weather to tan or yellow.

Exposures of Price River crop out extensively north of the North Fork of Salt Creek and along the southeast margin of the area. These two occurrences cannot be directly traced laterally to positively establish equivalence, but Schoff (1951, p. 627) identified and referred to both as Price River Formation in the Cedar Hills to the east. In the northern part of the Mount Nebo area, the formation forms conspicuous and prominent red outcrops in angular uncon- formity with the overturned lower limb of the Nebo anticline (Plate 5 ) .

A coarse red conglomerate with subordinate amounts of intercalated grit, coarse to medium grained sandstone, and a few algal limestone beds constitutes the Price River Formation as mapped. Conglomerate beds typically contain pebbles to boulders of buff, yellowish, purplish, dark gray, and red quartzite with lesser amounts of Cambrian through Pennsylvanian carbonates. T h e Cam- brian through Pennsylvanian carbonate clasts are smaller, less rounded and less common than the Cambrian and Precambrian quartzite. Sweral beds of algal limestone and algal limestone conglomerate locally occur and weather reddish and yellowish gray from a pinkish or brownish fresh color. Price River beds become obviously more coarse textured and red from east to west within the mapped area.

Approximately 1000 feet of Price River strata are present in Bear Hollow, a tributary to the North Fork of Salt Creek. In the Cedar Hills area to the east a few miles, Schoff ( 1 9 5 1 , ~ . 627-628) measured 1500 feet of the formation.

Price River beds are largely unfossiliferous. Spieker (1946, p. 132) reported fossils of Late Montanan age from the formation in the northern Wasatch Plateau, and Schoff (1951, p. 628) reported regional relationships pointed to a Late Montana age for the formation in the Cedar Hills, since it occurs strati- graphically above rocks containing Colorado age fossils.

7 2 B. ALLEN BLACK

The base of the Price River Formation marks a regional angular uncon- formity (Spieker, 1946, p. 122; Schoff, 1951, p. 628; Hunt, 1950, map; Hardy and Zeller, 1953, p. 1268; and Hardy, 1962, p. 57) . A similar regional (?) angular unconformity marks the upper contact with the North Horn Formation, at least in individual map areas (Hardy and Zeller, 1953, p. 1269-1270; Burma and Hardy, 1953, p. 550; Hardy, 1962, p. 58; and Hintze, 1962, p. 71 and map). Within the immediate map area, however, the North Horn Formation is absent, but the upper contact of the Price River Formation is angularly un- conformable with the younger Golden's Ranch Formation in the vicinity of Red Creek and the North Fork of Salt Creek.

Tertiary System Golden's Ranch Formation

The name Golden's Ranch Formation was proposed by Muessig (1951b) for a series of volcanic conglomerate, tuff, bentonite, sandstone, and other assorted sediments which overlies the Green River Formation on the Middle Fork of Sage Valley, the type localit),, on Long Ridge, Utah. Moroni Formation has been used by some workers for equivalent rocks in adjacent areas, but because this formal name was dropped by Schoff (1951, p. 634) who proposed it (Schoff, 1937, p. 105), and because of the lithologic and structural similarities between the volcanic and volcanic sedimentary rocks described by Muessig (1951a, p. 89-103) and those in the Mount Nebo area, the name Golden's Ranch Formation will be used in this report.

Stream deposited volcanic sediments and a few extrusive flows are wide- spread in the eastern half of the mapped area and are well exposed on tne North Fork of Salt Creek and its tributaries. A less extensive exposure also occurs on the south side of Salt Creek near its mouth. Characteristically the formation erodes to a subdued and vegetated topography.

The Golden's Ranch Formation consists of a fairly thick interval of ~nter- stratified water-deposited pyroclastic rocks and minor flows. White to greenish tuff, dark andesite volcanic conglomerate, and greenish to dark brown, friable, volcanic sandstone constitute the dominant rock types. Much of the formation was water-lain, as indicated by irregular stratification, local channeling, cross- stratification, and rapid facies changes. Dominant fragments are a dark brown to dark reddish, rounded, andesite pebbles, cobbles, or boulders. The formation accumulated on a surface of considerable relief and locally is interpreted to have been deposited in a Tertiary canyon whose trend approximately coincides with that of the lower part of the North Fork of Salt Creek.

The Golden's Ranch Formation is divisible into four distinct facies which correspond to fairly sharp changes in color, composition, and texture. They are in ascending order: (1 ) a crudely sorted and stratified andesite volcanic conglomerate with locally interbedded buff limestone which weathers to ro- duce a porous tuff-like exposure, ( 2 ) andesite volcanic conglomerate and L f f to white, water-lain tuff containing some pebbles of andesite and other vol- canic~, (3) a sequence of ~nterbedded pale greenish and dark brown, friable volcanic sandstone and a few dark andesite flows; and (4) a white or buff to pale greenish, conspicuously cross-bedded tuff containing andesite and other pebbles. The various subdivisions are traversed in ascending order from Pole Canyon up the North Fork of Salt Creek to Red Creek.

A stratigraphic section was not measured because of poor exposures, but 500 to 600 feet of Golden's Ranch strata are present on the North Fork of Salt

N E B 0 OVERTHRUST 73

Creek. Schoff (1951, p. 634) measured 1560 feet of equivalent beds in the Cedar Hills east of North Fork.

N o fossils were collected from the golden'^ Ranch Formation within the mapped area, but because the formation exhibits so many of the features described by Muessig (1951a, p. 89-103) from the type section on Long Ridge, an Eocene age is assigned to it in the Mount Nebo area as well. Muessig (195la, p. 97-99) reported finding an Eocene flora in the Sage Valley Limestone Member of the formation 820 feet above the underlying Green River Forma- tion. Since exposures of the Sage Valley Limestone Member occur on the North Fork of Salt Creek, a Medial Eocene or slightly younger age is assigned to the formation in the mapped area.

Contact with all younger formations in the Mount Nebo area is uncon- formable, locally angular. Undeformed Salt Creek Fanglomerate rests upon folded and eroded Golden's Ranch strata at numerous localities (Plate 5 ) .

Tertiary-Quaternary Systems ( ?) Salt Creek Fanglomerate

Eardley (1933a, . 336-338) named and defined the Salt Creek Fanglomer- ate for exposures o f red, crudely sorted conglomerate which crop out in Salt Creek Canyon (Plate 5 ) .

Salt Creek Fanglomerate deposits are more extensive than indicated by Eardley (1934, map) except in the eastern half of the mapped area where they are less widespread than what he mapped. Nevertheless, excellent exposures occur and typically occupy the high canyon-wall margins of the present drainage system. The best outcrops are located in Salt Creek Canyon, in Foote's Canyon, and to a lesser extent on the North Fork of Salt Creek.

The Salt Creek Fanglomerate is a pale to bright red, crudely sorted and poorly stratified conglomerate. It is typically composed of pebble to boulder size fragments of Pennsylvanian and younger rocks. The clasts have not been transported far and were probably locally derived from the High South Ridge- Mount Nebo vicinity, though along the south side of Salt Creek Canyon more quartzite is present which suggests the Gunnison Plateau also may have served as a source. At some outcrops the deposit appears to represent old stream fill while at others, stratification and sorting suggest an alluvial fan deposit. Distri- bution of Salt Creek Fanglomerate exposures leads the writer to the same con- clusion as Eardley (1933a, p. 337) who postulated the formation had been deposited on an old mature valley floor which subsequently has been incised to a depth of several hundred feet.

Thickness of the formation is variable from one outcrop to the next, but the maximum thickness observed is approximately 100 feet in Foote's Canyon near the Nebo Archery Range.

Eardley (1933a, p. 337-338) was unable to date the Salt Creek Fanglomerate accurately, but on the basis of physiography, he postulated a Pleistocene age for it. Muessig (1951a, p. 109) reported similar deposits on Long Ridge, but he favored an older age for them. The writer has nc new data to offer, and a tentative Late Tertiary to Pleistocene age is considered for the unit.

Quaternary System Old Alluvium

Large exposures of poorly sorted alluvium occur within the mapped area, especially at the head of Gardner's Canyon, on Ree's Flat, along the margins of

74 B. ALLEN BLACK

Quaking- Asp Canyon, at the head of Foote's Canyon, and on the south side of Salt reek (Plate 5 ) . Less extensive accumulations occur in Birch and Little Birch C~nyons, and .at the heads of Quaking Asp and Andrew's Canyons. These deposits represent a combination of several types of accumulations, for example, talus cones which grade downward and pass imperceptibly into fan and stream gravels, and old stream gravels which have been elevated and incised because of rejuvenation resulting from periodic movements along the Wasatch normal fault. Deposits at higher elevations are almost exclusively locally derived Pennsylvanian and Permian rubble. In the vicinity of Ree's Flat, Gardner's Canyon, and elsewhere, relationships between old and young alluvium point to several periods of recent uplift along the Wasatch fault, each being followed by an interval of incision, reworking of older debris, and accelerated erosion at higher elevations.

Young Al luv iu~~ i The present drainage system is the site of silt, sand, and gravel accumula-

tions. Stream and fan deposits are most conspicuous and some deposits are well exposed and attest to several periods of erosion and subsequent reworking. Such relations are visible at the mouth of Salt Creek Canyon where fairly well stratified stream gravels have been incised to a depth of 30 feet or more. Similarly, on the North Fork of Salt Creek in the vicinity of Red Creek, old stream gravels have been incised to depths of 20 to 30 feet below the old valley floor. Along the west side of Ree'sFlat, old alluvium attests to at least three distinct periods of erosion, each of which has resulted in successively younger stream gravels.

Most of these younger deposits show response to uplift along the Wasatch fault. Several distinct stream deposits could be mapped within the present drainage channels, especially in Salt Creek Canyon, in Foote's Canyon, in Rocky Ridge Canyon, and in the North Fork of Salt Creek.

IGNEOUS ROCKS

Other than the few andesite flows noted in the Golden's Ranch Formation, igneous rocks are uncommon, although several small lamprophyre sills and one prominent dike occur within the mapped area. The sills are only four to six inches thick, too small to be mapped, and occur in Permian strata northeast of Round Top Hill. A dull dark red to purplish andesite dike with silica-filled fractures is present on both the east and west sides of North Fork of Salt Creek two miles north of the junction of State Highway 11 and the Nebo Loop Road. I t is noticeably thicker east of the road than west and stands out in greater relief on the east also. Thickness is variable but ranges from approximately 1 0 feet on the west end to 100 feet on the east end.

The dike is interpreted as intrusive into the Golden's Ranch Formation though contact relations are obscured by float and vegetation. Beds on either side of it have the same attitude. It may have been emplaced during late stages of Golden's Ranch deposition because similar rocks occur there as clasts.

John (1964, p. 94) described intrusive and extrusive igneous rocks of the Levan area 10 miles to the south and expressed the opinion that the Moroni Formation (Golden's Ranch Formation equivalent) was derived from intru- sions of that area. It is also possible that they were partially derived from extrusive rocks north of the mapped area. Muessig (1951a, p. 97-100) showed

N E B 0 OVERTHRUST 75

that part o r all volcanic sedimentary rocks of Long Ridge were derived from igneous rocks of the Tintic District and the northern part of Long Ridge.

John (1964, p. 67) indicated igneous rocks w&e emplaced after Green River time, or post-Medial Eocene. Because of the relationships between the andesite dike and the Golden's Ranch Formation coupled with the age of in- trusions near Levan, the sills and dike of the Nebo area are tentatively regarded as late Eocene or slightly younger.

STRUCTURE General Statement

Structural relationships in the Mount Nebo area are a consequence of several episodes of tectonism. The Nebo anticline, the Nebo Overthrust and associated thrust faults, and a large anticline in the Arapien Shale constitute the major structural elements of the mapped area. hTumerous smaller folds and thrust faults exist in the Arapien Shale, but are small in comparison to the major structural elements, though significant to proper interpretation of the structure. Structural development in time is discussed in the section dealing with tectonics and geologic history.

Folds Nebo Anticline

The northwest quarter of the mapped area comprises part of a large over- turned anticline involving Precambrian through Jurassic rocks, and forming the dominant structural feature in the extreme Southern Wasatch Mountains. Mount Nebo is carved from the overturned eastern limb of the overfold which trends slightly each of north and extends from the vicinity of Quaking Asp Canyon northward a proximately 18 miles. However, in the Dry Mountain region the B fold is broa er and, so far as exposed, not overturned. Deformation appears to be greatest on the southern end of the structure, but this may be the result of subsequent thrusting and better exposures there than along the ~ a s t side of Mount Nebo where extensive vegetation and younger fohnations obscure rela- tionships. T h e western margin is truncated by the normal Wasatch fault which extends the entire length of the overfold remnant and nearly coincides with its axis. T h e southern margin is bounded by the Nebo Overthrust which is responsible for the overfold's present position. A belt of thick, less deformed Late Cretaceous and Tertiary sedimentary and volcanic rocks extends along the east margin of the Nebo anticline and in part covers the Nebo Overthrust (Plate 5 ) .

A small complex S-fold is well developed within the Nebo overfold remnant in the vicinity of Quaking Asp Canyon (cross-section Plate 5 ) ; presence of a distinctive brachiopod limestone bed at the top of the Grandeur Member and other distinctive lithologies in the Park City and Phosphoria Formations facili- tated mapping this structure. Similar complex modifications in the southern ends of other anticlines occur in the Wasatch Range at Buckley Mountain northeast of Springville, Utah, and American Fork Canyon northeast of American Fork, Utah. Since the S-fold within the mapped area is truncated by the Nebo Overthrust, the strata involved have been subjected to two compressive phases prior to thrusting which were oriented nearly at right angles to each other and occurred simultaneously or separately. Brady (1965) concluded that the Southern Wasatch Range had been subjected to two compressive pulses prior to thrusting. Greatest deformation was produced by east-west oriented

B. ALLEN BLACK

forces which resulted in formation of the major north-south trending structures in the Wasatch Range.

Folds in the Ara~ien Shale T h e major structure in the Arapien Shale is a north-south plunging,

asymmetrical anticline which is considerably modified by smaller folds and thrust faults. T h e northern portion of the anticline is covered by the southern portion of the Nebo Overthrust. Imbricate thrust faults, smaller folds, and a shale and gypsum breccia obscure the anticline along the west margin. T o the south the anticline gives way to a broad, less deformed syncline which forms the dominant structure of the Gunnison Plateau. The eastern portion of the anticline is concealed by the Golden's Ranch Formation and the Indianola Group. Cross-sections accompanying Plate 5 show this anticlinal structure.

A well defined, northerly trending, doubly plunging, asymmetrical anti- cline occurs in the Arapien Shale at the mouth of Salt Creek Canyon. It exposes bedded gypsum in its core. Steep dips along both flanks are interpreted to be the result of gypsum flowage from the limbs to the core region during folding. A small syncline in the northern nose of the anticline plunges north- ward beneath shale and gypsum breccia of unit two of the Arapien Shale, north of State Highway 1 1 near the old gypsum workings.

O n the north side of State Highway 1 1 opposite the mouth of Andrew's Spring Canyon, another minor anticline on the major structure trends approxi- mately N. 60-70' W. It is asymmetrical to the northeast, locally overturned and recumbent. Plate 3, fig. 1 shows the southeast plunging nose of this struc- ture, and Plate 2, fig. 1 shows a small displacement thrust fault which truncates and covers the northwest part of the structure, with unit two of the Arapien Shale thrust above unit three. Asymmetry to the northeast is believed to be the result of drag exerted on the axial portion of the anticline by the over- riding gypsiferous material and the structurally higher Neb0 Overthrust. Drag folds associated with the upper and lower plates of the minor thrust sub- stantiate this interpretation.

Along the west side of the canyon immediately south of the Ree's Flat Road and the old Nebo Power Plant, several small anticlines and sypclines occur in unit three of the Arapien Shale. They are gypsum-cored and trend approximately N . 40-50° E., with amplitudes of approximately 100 feet. They are asymmetrical to the southeast and extend laterally only a few hundred feet.

An symmetrical, and in part overturned, anticline occurs on the east limb of the major asymmetrical anticline of the Arapien Shale and is well exposed near the junction of State Highway 11 and the Foote's Canyon Road. It is doubly plunging, steeply to the south and less so to the north where the Nebo Overthrust and Foote's Canyon thrust truncate the structure. Overturning is to the northeast, and for the most part, the fold is developed in unit five of the Ara ien Shale. The Golden's Ranch Formation overlaps the eastern limb which is a f so coincident with the eastern limb of the major anticlinal structure of the Arapien Shale. The structure extends from near the Nebo Archery Range in Foote's Canyon southward to Rocky Ridge Canyon, south of Salt Creek.

At the intersection of Foote's Canyon and Salt Creek Canyon, a smaller synclinal structure occurs on the western limb of the previously described anti- cline. The fold is asymmetrical to the northeast and trends somewhat west of north. Several thrust faults of small displacement which exhibit drag and

N E B 0 OVERTHRUST

boudinage structures in the western limb indicate that this limb moved, rela- tively, easterly over the synclinal axis (Plate 4, fig. 2) .

A well developed syncline occurs within the fenster in Gardner's Canyon. Its axis trends approximately N. 40-50' E. and nearly coincides with the canyon bottom. It is asymmetrical to the southeast and is developed in unit one of the Arapien Shale. Pods of gypsum were observed along the north and south sides of the canyon, and presumably this fold was also gypsum-cored, as are nearly all the minor folds in the Arapien Shale.

Other Folds A northeasterly plunging, asymmetrical syncline whose north limb is in part

overturned to the southeast is formed in the outlier of Indianola rocks east of Ree's Flat (Plate 5 ) . T h e structural trend is clearly shown on aerial photos and was easily mapped, even though parts of it are covered by vegetation. Form and asymmetry suggest the structure developed in response to displacement of the Nebo overfold into this belt of Indianola clastics and underlying Arapien Shale.

Thrust Faults Nebo Overthrust

The Nebo Overthrust was first studied and named by Eardley (1934, p. 381- 385) , who attributed 12 miles of crustal shortening to the overturned Nebo anticline and approximately one additional mile to the Nebo overthrust. H e supposed the fault to be of small horizontal displacement because stratigraphic displacement dies out to the northeast.

Johnson (1959, p. 34) studied the Nebo Overthrust and suggested a stratigraphic displacement not in excess of five miles but not less than 14,900 feet. Inferred direction of movement according to him is east or southeast with maximum stratigraphic displacement occuring in the vicinity of Red Canyon where Desmoinesian Oquirrh rocks are in thrust contact with underlying Jurassic Arapien Shale (Johnson, 1959, p. 35-38). Amount of displacement stated by Johnson is still not enough to account for structural relationships between the upper and lower plate as now mapped.

The Nebo Overthrust is well exposed along the western and southern margins of Mount Nebo, but along the eastern side of the mountain is it partially covered by float and the Golden's Ranch Formation. The overthrust can be easily traced from the mouth of Red Canyon to the saddle at the head of Little Birch Creek where it is truncated by a normal fault associated with the Wasatch fault system (Plate 5 ) . The thrust fault is downfaulted to the west but erosion has exposed it in Little Birch Creek Canyon as a small fenster with overturned Oquirrh Limestone in the upper plate and locally overturned Arapien Shale and blocks of Nugget Sandstone in the lower plate (Plate 1, fig. 1). From where the normal fault crosses the saddle between Little Birch and Birch Creeks, the overthrust can be mapped continuously northward to Ingram Canyon with only minor interruptions by small normal faults (Plate 5 ) . The thrust can be traced up the north side of Ingram's Canyon to a point where it is displaced by another normal fault. The thrust fault is again exposed further up the canyon where it crosses the canyon and swings southerly. The overthrust can be followed continuously from here southward to the head of Red Canyon where it is buried below stream gravels along the west margin of Ree's Flat. - -

Throughout the above area, the Nebo Overthrust sharply separates over- turned Oquirrh rocks in the upper plate from nearly flat or locally overturned

78 B. ALLEN BLACK

Nugget Sandstone or Arapien Shale of the lower plate. Exposure of the over- thrust in this vicinity is greater than was realized by previous workers.

The thrust zone is concealed for the most part from Ree's Flat to Foote's Canyon, but the writer is certain that it is present because lowermost exposures in the displaced Nebo anticline are overturned Ankareh beds, separated by alluvium, Indianola, and Salt Creek deposits from underlying upright unit five of the Arapien Shale. Thrust trace is shown on Plate 5 in an inferred position where covered.

Northeast of Foote's Canyon the thrust fault emerges from beneath Salt Creek Fanglomerate and can be traced to the east side of Mahoga,ny Hill but there the trace is covered by float. On Mahogany Hill the lowermost beds in the upper plate are overturned oolitic and very thin bedded limestones of unit one in the Arapien Shale. Highest rocks in the lower plate are ap arently u p

the upper plate of the Foote's Canyon thrust. e right Nugget and Ankareh strata (Plate 2, fig. 2 ) . The latter roc s constitute

F;& Mahogany Hill north to the North Fork of Salt Creek, the Nebo Overthrust cannot be certainly traced because vegetation on the east side of Mount Nebo is dense and outcrops are poor. The fault continues into this area, nevertheless, for lowermost exposures in the Nebo overfold are overturned lime- stone of the Araplen Shale (unit one). These rocks crop out sporadically from Mahogany Hill to the North Fork of Salt Creek but beyond are buried beneath the Price River Formation. An inverted sequence of Nugget Sandstone through Oquirrh Formation overlies these limestones. This inverted sequence can be similarly traced without difficulty to the North Fork of Salt Creek where it also passes beneath the angular unconformity at the base of the Price River Formation (Plate 5 ) . Unit six of the Arapien shale occurs to the east of this complete but inverted sequence, from Salt Creek Canyon to the North Fork of Salt Creek. This unit has a diagnostic color and lithology and forms the youngest stratigraphic unit in the exposed Arapien Shale in the eastern limb of the major anticlinal structure. The trace of the Nebo Overthrust coincides with the contact between unit six of the Arapien Shale and the inverted sequence. The thrust trace was approximately located between exposures of unit six and the lowermost exposures of the inverted sequence. Unit six is easily eroded to form valleys and flat-lying lowlands but lowermost strata in the overfold are more resistant and form hllls and strike ridges. -

Since unit six and the strata of the overfold pass beneath the Price River Formation in angular unconformity, the youngest age limit for the Nebo Over- thrust is obtained, if the strata above the angular unconformity are really Price River Formation. It is possible that they are not because they cannot be directly traced into Price River strata elsewhere. An unequivocal upper age limit for thrusting in the Southern Wasatch Mountains must await positive paleontologic dating of the rocks referred to as Price River Formation in this report.

The deformation zone associated with the Nebo Overthrust is more complex. Where competent rocks of the upper plate are in juxtaposition with competent rocks of the lower plate, a gouge and breccia zone several tens of feet thick commonly exists. If upper plate competent rocks are in thrust contact with lower plate incompetent rocks, the opposite is the case, that is, a relatively narrow and sharply defined zone of shale gouge and breccia occurs. On the other hand, it is not uncommon to observe large slices of Triassic and Jurassic rocks which have been sheared off the upper plate during movement and have been

caught along the thrust surface. Such is the case in the vicinity of Round Top Hill and Ingram's Canyon (Plate 1, fig. 2 ) . These slices are important struc- tural elements and provide clues to the displacement of the Nebo Overthrust. For example, Miner's Ridge is composed of a large slice of overturned Nugget Sandstone and unit one of the Arapien Shale, both of which pass beneath the Nebo Overthrust near the base of Round T o p Hill (Plate 5 ) . Their counterpart, however, is located on Mahogany Hill east of Mount Nebo.

Attitudes of the thrust surface were not directly measurable in the field, but the map pattern shows the thrust dips westerly along its extreme western trace, except in the vicinity of Gardner's Canyon and Round Top Hill where it dips to the southwest. T h e eastern trace along the west side of Mount Nebo indicates a nearly horizontal o r slightly easterly dip in the northern part of the area and a southwesterly dip in the vicinity of Gardner's Canyon and Round Top Hill. Along the southern margin of High South Ridge the fault d i p northerly and along the east side of Mount Nebo it dips gently westward (Plate 5 ) . O n a regional basis, however, the dip of the overthrust is north or northeast at a fairly low angle. -

These different attitudes can be interpreted to mean that the thrust plane has been subse uently folded or that the original thrust surface was quite irregular. T h e Iormer interpretation in preferred, for later compressive d i r turbances did affect the Mount Nebo area. Brady (1965) came to a similar conclusion regarding the Santaquin Overthrust, approximately 18 miles north of the mapped area, which is considered to be the northern extension of the Nebo Overthrust by Brady and the writer.

Discontinuous exposures of unit one of the Arapien Shale were observed projecting through the Price River and younger formations for a mile or so north of the mapped area west of Red Creek and north of North Fork. A greater thickness of the formation occurs in the lower limb of the Nebo overfold as it is traced northeast. This was expected by the writer since it seems logical that the thrust fault would remain in the incompetent rocks which act as a lubricant and cut down section in them to the gypsiferous portion as it is traced northward. The implication is that the Deer Creek, Charleston, Strawberry, Santaquin, and Nebo thrusts are all genetically related and probably connected at depth, as has been suggested by Baker et a1 (1949, p. 1196) and Bissell (1952, p. 622).

Recent investigations by Brady (1965) in the West Mountain-Santaquin Canyon-Payson area revealed a partial fenster near the mouth of Santaquin Canyon. Rocks as old as Precambrian occur in thrust contact with Oquirrh rocks along the Santaquin Overthrust and along the northern margin of the fenster. Brady postulated that the Santaquin Overthrust is the northern extension of the Nebo Overthrust. The writer concurs because the Nebo thrust fault has a northerly dip in the mapped area and cuts down section and the Santaquin thrust has a southerly regional dip as mapped by Brady (1965, Text-fig. 5). The Nebo overfold can be traced continuously northward to where the fold is developed on the upper plate of the Santaquin Overthrust.

Foote's Canyon Thrust In Foote's Canyon badly broken but apparently upright ( ? ) Nugget, An-

kareh, and Thaynes strata of the lower plate of the Nebo Overthrust constitute the upper plate of a lower major thrust fault involving Permian through Jurassic rocks. This lower thrust is here named the Foote's Canyon thrust since the best

80 B. ALLEN BLACK

exposures occur along the east side of Foote's Canyon near the Nebo Archery Range (Plate 5 ) .

The Foote's Canyon thrust is continuously exposed southward from the mouth of the north trending tributary in Foote's Canyon across the ridge of Foote's Canyon, and then northeasterly across the adjacent drainage to where the trace is covered by Golden's Ranch Formation (Plate 5 ) . In tracing the thrust fault one goes from Permian to Jurassic rocks in the upper plate and from unit five to unit six of the Arapien Shale in the lower plate. Arapien beds are upright and dip eastward or northeastward to form the east limb of the previously described major anticline in the Arapien Shale. Near the head of Maple Spring Hollow the overthrust is only approximately located.

- -

The upper plate of the Foote's Canyon thrust is composed of thinned and overturned imbricate slices of various formations. The upper plate of the Foote's Canyon thrust, then, can be thought of as a series of large slices of considerably deformed and thinned Permian through Jurzssic formations which have been caught beneath the sole of the Nebo Overthrust.

Thrust Faults in the Arapien Shale Several small low angle thrust faults were observed and mapped in the

Arapien Shale. They are located north and south of State Highway 11 between the Ree's Flat Road and the mouth of Foote's Canyon (Plate 5 ) . Though these faults are small, they are nevertheless significant to interpretation of thrusting within the mapped area. They are well exposed in gully bottoms and draws even though they cannot be traced laterally any great distance. Many other similar faults doubtless exist but were not mapped, for the badland topography on the eroded Arapien Shale makes observation of all outcrops impossible; even so, two months were spent mapping details of these minor structures.

Nature, Direction, and Displacement of Thrusting Drag structures associated with minor thrust faults in the Arapien Shale

indicate, in every instance, that the upper plate moved eastward relative to the lower plate. Drag folds in shale sequences of both plates substantiated the same movement, with competent layers moved eastward over incompetent layers, re- sulting in local overturning of beds. Shear zones associated with these small thrust faults also indicate the same direction of movement.

Distribution and attitude of slices along the Nebo Overthrust suggests that each was sheared from the base of the upper plate and lagged behind as the sheet advanced eastward. Miner's Ridge rocks once constituted part of the upper block of the Nebo Overthrust, but they were subsequently detached and overridden by the remainder of the upper plate. The displaced northern continua- tion of the Miner's Ridge sequence is in Foote's Canyon and to the northeast, where identical strata with similar attitudes and structural relations are present along the Nebo Thrust Trace. Other examples also suggest that the Nebo over- fold has been displaced eastward over lower plate rocks.

Slickenside bearings obtained from the various localities and average direction of overturning indicate the direction of movement is clearly toward N. 60' to 70' E. Drag and drag folds associated with the minor thrust faults in the Arapien Shale substantiate this direction of movement, and the convex east- ward structure of the Southern Masatch Mountains, as shown in the 1963 Utah State Geologic Map, also supports this interpretation.

PLATE 1 - B. ALLEN BLACK

FIG. I.-Mount Nebo and High South Ridge from the south. Rocks at lower left are overturned and thrust Oquirrh Formation resting on slices of overturned Thaynes, Ankareh, and Nugget strata. The ridge on the lower right is composed of over- turned Nugget and Arapien beds in thrust contact with underlying Park City and Phosphoria rocks. PPo. Oquirrh Formation; Ja, Arapien Shale; Jn, Nugget Sandstone.

FIG. 2.-Trace of the Nebo overthrust near the head of Birch Canyon. Rocks in the lower plate are upright Nugget Sandstone ( J n ) and Arapien Shale ( J a ) , and Oquirrh rocks (PPo) form the upper plate.

N E B 0 OVERTHRUST

PLATE 2 - B. ALLEN BLACK

FIG. 1.-Overturned Arapien Shale, unit three, beneath overthrust unit two, on the flank of a gypsum-cored anticline north of State Highway 1 1 , opposite Andrew's Spring Canyon, as seen from the east.

FIG. 2.-Trace of the Nebo overthrust on Round Top Hill with Park City rocks above overturned slices of Woodside, Thaynes, Ankareh, Nugget, and some Arapien gypsiferous rocks.

THRUST FAULTS NEB0 AREA

PLATE 3 - B. ALLEN BLACK

FIG. 1.-A gypsum-cored anticline in the Arapien Shale north of Utah State Highway 11, opposite Andrew's Spring Canyon, as seen from the west.

FIG. 2.-Drag folds along a thrust in the Arapien Shale, unit three, north of Utah State Highway 11, opposite Andrew's Spring Canyon.

FOLDED ARAPIEN SHALE

PLATE 4 - B. ALLEN BLACK

FIG. 1.-Trace of a thrust fault in unit three of the Arapien Shale, north of Utah State Highway 1 1 in Salt Creek Canyon, opposite Andrew's Spring Canyon. Drag is not obvious in the photograph, but is readily apparent in the field.

FIG. 2.-Small thrust fault in unit three of the Arapien Shale as exposed in the first road cut west of Foote's Canyon Road on Utah State Highway 11. Drag is well developed even on these small structures.

FAULTED ARAPIEN SHALE

N E B 0 OVERTHRUST 8 1

Structure sections of Eardley (1934, map) and Johnson (1959, map) show considerable similarity in interpretations of the upper plate by these two workers and the present writer, since the structure of the upper plate of the Nebo Over- thrust is relatively simple (Plate 5 ) . Local differences do exist. however, for in the vicinity of Quaking Asp Canyon the complex S-fold in the upper plate is lacking in Johnson's structure sections. -

Variations in interpretation of lower plate structure exist between all workers and these are readily apparent when the various structure sections are compared (Plate 5) . Eardley (1934, Map) shows structure of both the upper and lower plates as essentially the same, except that the upper plate has been displaced eastward approximately one mile. On the other hand, Johnson (1959, map) shows the upper plate resting on an entirely different lower plate struc- ture, though the structure section is constructed to suggest he interpreted the westernmost portion of this lower plate to originally coincide with that of the Nebo overfold prior to displacement. Both Eardley's and Johnson's structure sections are constructed along nearly the same line although Eardley's is further north than Johnson's. It is obvious from the cross sections why Eardley (1934, p. 385) attributed only one mile of displacement to the Nebo Over- thrust, and why Johnson (1959, p. 34) postulated a maximum of five miles of movement.

Structure sections accompanying the present report document more struc- tural details for both the upper and lower plates of the Nebo Overthrust and indicate considerably more than five miles of displacement is required to account for the observed structural relationships.

Directional properties and nature of movement associated with the Nebo Overthrust suggest that statements of Eardley (1934, p. 381), Johnson (1959, p. 34), and Muessig (1951a, p. 138-139) concerning a remnant of an overfold on Long Ridge to the west of Mount Nebo may have more significance than previously thought. Muessig's (1951a) map and the one accompanying this report, when placed in proper spatial relation, reveal striking similarities. The Long Ridge remnant of the overturned anticline and the one in the upper plate of the Nebo Overthrust are nearly identical in attitudes and geometry. Dips on Long Ridge are steeper for similar parts of the structure. Differences in attitude can be explained by recalling that structures generally die out at depth, and so the steeper dips at Long Ridge merely indicate the structure is righting itself. The writer concludes that the remnant in Long Ridge to the west and the one occurring within the mapped area constituted, at one time, the same great overfold, but that the remnant at Long Ridge is part of the lower plate of the Nebo Overthrust and the Nebo overfold in the map area repre- sents the displaced upper part of this large overturned anticline. Displacement is considered to be at least seven miles and possibly as much as ten miles toward N. 60' to 70' E. The structure sections (plate 5 ) show the entire upper plate must be moved west of the present position of the normal ~asatch-fault , -and even then structures of the upper and lower plates do not match.

Additional evidence favoring this magnitude of movement is also available as a consequence of Brady's (1965) work to the north of the mapped area. He reported ~iecambrian strata in juxtaposition with Oquirrh rocks (~enns~lvanian- permian) which requires a stratigraphic displacement of several miles (Brady, 1965, Text-fig. 5).

8 2 B. ALLEN BLACK

Normal Faults Wasatch Fault

A conspicuous recent fault scarp, the result of renewed movement along the Wasatch normal fault, can be traced from near the toe of the alluvial fan at Red Canyon northward past Willow Creek Canyon and north of the mapped area (Plate 5) . The fault surface, with an attitude of N . 45OE., 71°NW, is well exposed at the mouth of Little Birch Creek Canyon. Tension fractures and slickensides are remarkably well shown, the latter having a rake of 74O SW suggesting a small strike-slip component of movement.

Plate five shows the Wasatch fault and its irregular pattern. Deformation associated with it varies from simple to complex. Oquirrh strata in the foot- wall, on the east, are extensively fractured and brecciated. An extensive-breccia zone at the mouth of Willow Creek Canyon, noted by Johnson (1959, map) is interpreted to be the result of intersection of the Wasatch fault and the Nebo Overthrust, the latter believed to be just below the canyon floor.

All north-south trending normal faults along the western margin of Mount Nebo are interpreted to be similar to the parallel Wasatch fault in genesis, attitude, and time of formation. They dip steeply westward, with hanging walls always down to the west. Many associated faults are too small to map on the present scale, but the major ones have been located. 'fie faults are commonly marked by fractured and brecciated zones which frequently coincide with topographic depressions.

Displacement on various faults range from a few tens of feet to several hundred feet. Movement must amount to several thousand feet for the Wasatch fault since no bedrock has been penetrated by drilling in Juab and associated valleys, to the knowledge of the writer. However, Eardley (1933a, p. 245) found exposures of the hanging wall near Santaquin Canyon which revealed at least 5500 feet of stratigraphic throw along the fault, and he conservatively cstimated that it was probably 6000 feet further south (Eardley, 1933a, p. 245).

Exact age of the Wasatch and related faults, which are considered a result of Cenozoic Basin and Range deformation, is impossible to determine within the area investigated for no Tertiary rocks are seen to be involved in the faulting. There is evidence of recent activity, however, along the Wasatch fault. The allu- vial fan at the mouth of Red Canyon and alluvial deposits at the mouths of Gardner's Canyon, Birch Creek Canyon, and Willow Creek Canyon have been offset up to 20 feet or more by recent movement. Physiographic evidence along the trace of the Wasatch fault strongly suggests that it has been intermittently active ever since it was initiated.

Cow Hollow Fault The Cow Hollow fault is a steeply eastward dipping normal fault. This

fault was not mapped by Eardley (1934), but it occurs in the vicinity of the Pines Campground on the North Fork of Salt Creek. Displacement along the fault amounts to only a few hundred feet.

The Cow Hollow fault extends from the area of soft ground and springs northeast of Mahogany Hill northward across Salt Spring Creek, the North Fork of Salt Creek, and along the west side of Cow Hollow and through the saddle at its headwaters, where it apparently dies northeastward (Plate 5 ) . The fault zone is seldom exposed, except along the west side of Cow Hollow where a breccia zone of Arapien Shale and Price River Formation occurs, but the zone coincides with a break in topography along its entire trace. Southwest of the

N E B 0 OVERTHRUST 8 3

North Fork of Salt Creek, it was difficult to trace the fault because of dense vegetation and poor exposures.

N o data are available to date the fault accurately, but because of its trend and invclvement of the Golden's Ranch Formation (?), it is correlated with the other Basin and Range faults and is Late Eocene or younger.

Transverse Normal Faults Numerous small transverse oblique-slip normal faults occur in the vicinity

of North Fork of the Salt Creek and below the Nebo Overthrust in Birch Creek Canyon. Those in the North Fork dip moderately to steeply northward and have hanging walls consistently down and to the east based on attitudes and slickenside rake. They are conspicuously expressed in the ledgy topography of the Park City and Phosphoria Formations. Major ones are shown on Plate 5. These faults occur only between Andrew's Canyon on the south and the major angular unconformity on the north. The fault with greatest displacement, a stratigraphic separation of over 500 feet, coincides with the axis of the norther- most tributary of Andrew's Canyon (Plate 5 ) .

Several similar faults occur in Birch Creek Canyon below the trace of the Nebo Overthrust (Plate 5 ) , but here relationships are reversed from those in North Fork. T h e hanging wall is consistently down and slightly to the west, southwest of the traces. displace men^ is not great nor is it possible to follow their trace very far. It is not known whether they disrupt the Nebo and associated thrusts faults or pass under them, although transverse faults in the North Fork area occur in the upper plate of the Nebo Overthrust and are therefore younger. These transverse faults are interpreted as post-thrusting adjustments prior to Basin and Range faulting.

Normal Faults in the Arapien Shale Numerous small local normal faults were observed in the Arapien Shale,

but only a few were mapped (Plate 5 ) because of poor exposure and lack of any great lateral continuity. Two systems were recognized, one trending northerly and the other trending easterly. Nature of movement can-be ascertained on the basis of associated drag in incompetent beds. Deformation zones are typically very narrow and consist of a shale gouge and calcite filled fractures.

TECTONISM General Statement

Formations occurring within the Mount Nebo area attest to several episodes of Mesozoic and Cenozoic tectonism beginning with the Cedar Hills orogeny and culminating in the Basin and Range deformation which is still in progress. At least four and possibly six compressive disturbances, and at least two episodes of normal faulting have affected the various formations. Each younger deforma- tion has successively superimposed its effects on the older structures.

Cedar Hills Orogeny

The Cedar Hills orogeny was proposed by Eardley (1949, p. 13-16) for a compressive disturbance reflected in extensive deposits of coarse clastic Indianola rocks in the Cedar Hills east of Mount Nebo.

Spieker (1946, p. 126-130) first pointed out the significance of the Indianola Group and postulated a belt of strong folding and thrusting not far west of the present Southern Wasatch Mountains which served as the source

84 B. ALLEN BLACK

area for the clastic unit and related deposits. Intensive folding and thrusting must have occurred because rocks as old as Precambrian and Cambrian quartzites are recognizable in the Indianola Group. The Arapien-Indianola angular uncon- formity lnd~cates proximity to the fold belt, as does the texture of the clastic unlt. Vertical distribution of coarse conglomerates in the Indianola suggests two movements separated by a period of quiescence during which a middle finer-textured marine sequence was deposited.

The writer concurs w ~ t h Spieker's (1946, p. 120-152) Interpretation of the Indianola Group as a synorogenic deposit and also accepts the approximate location of the deformed belt, but he disagrees ~n interpretation that the Arapien Shale-Indianola Group contact is conformable. The Arapien Shale- Indianola Group contact is an angular unconformlty, though the angular dis- cordance is not great and can be seen from Salt Creek Canyon along the northern end of the Gunnlson Plateau. Hunt (1950, text and map) and Hardy (1962, p. 54) earlier pointed out this relationship. Significance of the angular unconformity is that the Cedar Hills orogeny did warp strata up to and including the Twist Gulch Formation in the Southern Wasatch Mountain- Gunnlson Plateau region. Though the deformation was not great it points out the proximity of the mapped area to the Cedar Hills orogenic belt. An area immediately west of a north-south line through the Canyon Range probably coinc~des wlth the deformed belt. Christiansen (1951, p. 9) reported approxi- mately 12,000 feet of Indianola strata along the east flank of the Canyon Range, a thickness almost as great as that reported by Schoff for the Cedar Hills. Spieker (1946, p. 150-152) and Eardley (1962, p. 293-294) believe the deformed zone extended from southern Nevada to southeastern Idaho since deposits similar in age and character to those of the Indianola group coincide with this belt.

The only signlflcant structure produced in response to the Cedar Hills orogeny within the mapped area is the angular unconformity between the Arapien Shale and the Indianola Group. Only broad-scale foldlng of the Arap~en and older rocks can be attributed to this disturbance.

Precise age of folding cannot be ascertained because the basal portion of the Indlanola Group has not yielded any diagnostic fossils and the upper age llmit of the Arapien Shale is still unknown. Schoff (1951, p. 625-626) and Hunt (1950, p. 52) have reported Coloradoan fossils from the middle marine portion of the Indianola, but in both instances well above the base of the group. The disturbance has been regarded as Mid-Cretaceous (Spieker, 1946, p. 150; Eardley, 1962, p. 293).

Laramide Orogeny Montana Phase

Spieker's (1946) work provided the basis for differentiating between varlous episodes of orogeny in central Utah. His recognition and interpretation of the Indianola Group as an orogenic deposit older than Laramide is significant since the term Laramide had been used previously to include almost any episode of diastrophism recorded in strata of the Wasatch Range.

Spieker (1949, p. 152) made another contribution with respect to the Montana phase of the Laramide orogeny. H e showed that the Price River always overlies the Indianola with angular unconformity. The orogenic event reflected in this contact was referred to as the Early Laramide orogeny by

N E B 0 OVERTHRUST

Spieker (1946, p. 152) and was dated as being Medial to Late Montanan on the basis of the angular unconformity and other regional relations.

The angular unconformity between the Price River Formation and Indianola Group is exposed along the southeastern margin of the mapped area and eastward in the Cedar Hills (Schoff, 1951, p. 628). Indianola strata are steeply dipping to overturned and the Price River Formation is moderately to steeply dipping and strikes obliquely to the Indianola beds, truncating them along strike (Schoff, 1951, p. 628 and map).

Dating of the orogeny within the Mount Nebo area hinges on correct identification of conglomeratc in the northern part of the area. Schoff (1951, p. 627) identified part of these as Price River Formation. Assuming that these conglomerates are equivalents of the type Price River Formation, most of the structures within the mapped area associated with the Nebo overfold and thrust are pre-Price Riveran.

The Nebo anticline and the Nebo and Santaquin Overthrust are post- Indianola, if the proposed root zone at Long Ridge is correct, and pre-Price River Formation, since this unit overlaps the Nebo Overfold in the North Fork-Red Creek area.

Paleocene Phase A more mild, post-Montanan phase, disturbance affected the south-central

and Southern Wasatch Mountains, Gunnison Plateau, and contiguous areas north and south. It consisted only of gentle folding or slight modification of earlier formed folds probably with some normal faulting.

Proof of this disturbance is not immediately available within the Mount Nebo area, but evidence of movement can be seen in the area north of North Fork and Red Creek, in the Cedar Hills to the east, and in the Gunnison Plateau to the south. North of North Fork and Red Creek, Price River strata have been partially or completely removed by erosion prior to deposition of the North Horn Formation, resulting in slight angular discordance between these two units. Schoff (1951, p. 629-630) reported a normal and interfingering contact for the Price River and North Horn Formations in the Cedar Hills area, but Hintze (1962, p. 71) pointed out that the contact is one of the most striking examples of an angular unconformity he had ever seen on aerial photo- graphs. Burma and Hardy (1953, p. 551) reported an angular unconformity between the two formations along the east side of the Gunnison Plateau and indicated ndrmal faults truncate the Price River Formation but are overlapped by the North Horn Formation. They discussed the regional significance of the contact and postulated a pre-North Horn orogeny (Burma and Hardy, 1953).

The exact date of this disturbance is unknown, but it is certainly post- Price River Formation, of Medial to Late Montana age, and pre-North Horn Formation, assigned a Paleocene age in the Cedar Hills by Schoff (1951, p. 630) . If the North Horn Formation is considered to be an orogenic and post- orogenic conglomeratic deposit, then the deformation took place during Late Cretaceous and Early Paleocene.

Eocene Phase Probably two pulses of orogeny affected Mount Nebo and vicinity during the

Eocene Epoch. Data concerning the first deformation is not available within the mapped area because no exposures of the rocks involved were found, though evidence from contiguous areas suggests they were probably deposited here but were subsequently eroded.

B. ALLEN BLACK

The central Utah region was subjected to broad-scale folding and normal faulting following deposition of the North Horn through Green River Forma- tions. It was at this time, presumably, that the Gunnison and Wasatch Mono- clines were initiated (Spieker, 1949, p. 80; Hunt, 1950, p. 147) . Gentle folds in the Price River through Colton strata north of the mapped area were probably initiated at this time. Axes of these younger folds are arcuate, convex eastward, and more or less coincide with the arcuate pattern of the Nebo over- fold. Structural development of these younger folds may have been controlled, in large measure, by pre-existing structures.

A deformation of slightly greater intensity occured during Late Eocene, possibly continuing into Oligocene, affecting units as young as the Golden's Ranch Formation. Deformation was preceded by a period of vigorous erosion which probably resulted in complete removal of North Horn through Green River rocks from the mapped area and developed the irregular pre-Golden's Ranch Formation topography. The erosion interval was contemporaneous with or followed by an active period of vulcanism and normal faulting, both of which were accompanied by penecontemporaneous erosion of the extruded volcanics and deposition of the eroded volcanic debris to constitute the Golden's Ranch Formation.

The Golden's Ranch Formation was folded and faulted, though exposures within the immediate map area d o not exhibit intensive deformation. Exposures north of the mapped area and those reported by Muessig (1951a, p. 156) in Long Ridge attest to fairly intensive deformation. Numerous small transverse normal faults d~srup t the unit in the Mount Nebo region, but since none of these faults are sufficiently large enough to trace laterally any great distance, it is not known whether faulting was contemporaneous with deposition or later, or both. Muessig (195 la , p. 151-1 5 5) indicated pre-volcanic, syn-volcanic, and post-volcanic faulting at Long Ridge. It is probably safe to assume that similar activity characterized the Mount Nebo area. Golden's Ranch strata exhibit gentle folding opposite the mouth of Pole Canyon.

Time of this disturbance is not known because the only post-Eocene forma- tion present within the mapped area is the Salt Creek Fanglomerate. It is undeformed and angularly overlies the folded and eroded edges of the Golden's Ranch Formation. Because the Sage Valley Limestone Member of the Golden's Ranch Formation outcrops were found on the North Fork of Salt Creek, the disturbance is surely post-Medial Eocene, but this does not preclude that deformation extended into or was initiated in the Oligocene. An upper age limit cannot now be assigned.

Basin and Range Deformation

Closing events of the Laramide orogeny set the stage for later Basin and Range faulting which roughly coincides with axes of the earlier highly de- formed major folds of the Wasatch Range and vicinity. Difference of opinion still exist concerning the age of initiation of faulting. Many geologists believe it began sometime in the Oligocene Epoch while others argue that it was not initiated until sometime in the Miocene Epoch. Since n o exposed rocks of Tertiary age are involved in the Wasatch and related faults along the western or eastern margins of the mapped area, no additional data can be given concern- ing the age of this fault activity in the Southern Wasatch Mountains.

The Wasatch and related normal faults along the western margin of Mount Nebo and the Cow Hollow fault along the eastern side are believed to be a

N E B 0 OVERTHRUST

consequence of this episode of faulting. Many of the small displacement, north- south trending, high angle faults in the Arapien Shale probably formed at this time. Basin and Range faulting is believed to post-date transverse faults in the northern and western part of the mapped area. Normal faults appear to truncate transverse faults in the vicinity of Birch Creek Canyon, but this relationship cannot be conclusively demonstrated.

SUMMARY AND CONCLUSIONS

Briefly stated the results of the investigation with respect to the Nebo Overthrust are these: Mount Nebo , has been displaced from at least as far west as the present position of Long Ridge in an easterly direction along an approximately N . 60-70' E. line, at least seven miles and probably as much as ten miles. This statement is based on the following points:

( 1 ) Paleozoic and Mesozoic rocks are locally and regionally overturned easterly and are resting on upright Mesozoic rocks, commonly Jurassic, of the lower plate where the latter are exposed.

( 2 ) Facies and thickness differences d o exist between similar stratigraphic units in the upper and lower plates (see Baker, 1947; Baker rt a/, 1949).

( 3 ) Measurements of drag associated with thrust faults in the Arapien Shale, and drag folds and direction of overturning of beds affected by the thrust faults, both major and minor, substantiate the direction of movement to have been along a N . 60-70° E. line with the upper plates consistently moving, relatively, easterly up and over the lower plates.

(4) Slickenside bearings obtained from the main overthrust zone and dis- tribution of slices caught along the thrust fault further indicate the aforementioned nature and direction of movement.

( 5 ) Overturned strike ridges in the Arapien Shale which formed in re- sponse to the easterly advancing Nebo Overthrust also attest to movement along a N . 60-70° E. line with the upper plate moving easterly up and over the lower plate.

( 6 ) In addition, the similarity between the overfold remnant at Long Ridge and the one in the upper plate of the Nebo Overthrust at Mount Nebo is too great to be casually overlooked or cast aside. The two remnants are identical in attitude, lithologies, stratigraphy, thickness, and structural trend. The Long Ridge overfold, then, is designated as the root zone for the Nebo overfold and overthrust, but this is not to suppose that the remnant at Long Ridge is in its proper spacial position relative to other rocks of that vicinity.

( 7 ) The overfold and overthrust developed in response to Laramide forces during the Montanan phase of the Laramide orogeny and both are dated as Medial to Late Montanan age on the assumption that so-called Price River strata overlapping the overfold in the northern portion of the mapped area are really lateral quivalents of the type Price River Formation. Conclusive proof of age is lacking as these strata cannot be traced laterally to the type Price River nor have they yielded diagnostic fossils.

88 B. ALLEN BLACK

REFERENCES CITED

tsker, A. A,, 1947, Stratigraphy of the Wasatch Mountains in the vicinity of Provo. Utah: U. S. Geol. Survey Oil and Gas Invest. Prelim. Chart 30. -- , and Williams, J . S., 1940, Permian in parts of Rocky Mountain and Colorado

Plateau regions: Amer. Assoc. Petrol. Geol. Bull., v. 24, p. 617-635. -- , ef al, 1949, Paleozoic geology of north and west sides of the Uinta Mountains,

Utah: Amer. Assoc. Petrol. Geol. Bull., v. 33, p. 1161-1197. Bissell, H. J., 1952, Stratigraphy and structure of the northeast Strawberry Valley

quadrangle, Utah: Amer. Assoc. Petrol. Geol. Bull., v. 36, p. 575-634. ---- , 1962, Pennsylvanian-Permian Oquirrh Basin of LJtah: Brigham Young Univ.

Geol. Studies. v. 9. ~ t . 1. P. 26-47. Boutwell, J. M., 1907: .Stratigraphy and structure of the Park City Mining District.

Utah: Jour. of Geol., v. 15, p. 434-458. . 1912, Geology and ore deposlts of the Park City Mining District. Utah: I1.S. Geol. Survey ~ r o f . ' ~ a ~ e r 77, 23i p.

-

---- , 1933, The Salt Lake Region: 16th International Geological Congress, Guide- book 17. 149 p.

Brady. M. J.. 1965, Thrusting in the Southern Wasatch Mountains. Utah: Brigham Young Univ. Geol. Studies, v. 12, p. 3-53.

Burma, B. H., and Hardy, C. T., 1953, Pre-North Horn orogeny in Gunnison Plateau, Utah: Amer. Assoc. Petrol. Geol. Bull., v. 37, p. 549-553.

Christianson. F. W., 1951, A Summary of the structure and stratigraphy of the Canyon Range. Utah: Utah Geol. Soc., Guidebook to the Geology of Utah. no. 6 , p. 5-18.

Eardley, A. J., 1933a, Stratigraphy of the Southern Wasatch Mountains, IJtah: Mich. Acad. Sci.. Arts and Letters, Papers, v. 18, p. 307-344.

---- , 1933b. Strong relief before block faulting in the vicinity of the Southern Wasatch Mountains, Utah: Jour. of Geol., v. 41, p. 243-267.

---- , 1934, Structure and physiography of the Southern Wasatch Mountains, Utah: Mich. Acad. Sci., Arts and Letters, Papers, v. 19, p. 377-400.

---- , 1949, Structural evolution of Utah, in Hansen, G. H., and Bell, M. M., The Oil and Gas Possibilities of Utah: Utah Geol. and Mineral. Survey, p. 10-23.

---- 1962. Structural Geology of North America: Harper Bros., New York, 743 p. Gale. H. S.. and Richards, R. W.. 1910, Preliminary report on the phosphate deposits

in southeastern Idaho and adjacent parts of Wyoming and Utah: U.S. Geol. Survey Bull. 430-H, p. 457-535.

Hardy. C. T.. 1952, Eastern Sevier Valley, Sevier and Sanpete counties Utah: Utah Geol. and Mineral. Survey Bull., v. 43, 98 p.

---- , 1962, Mesozoic and Cenozoic stratigraphy of north-central Utah: Brigharn Young Univ. Geol. Studies, v. 9, pt. 1, p. 50-64.

---- , and Zeller, H . D. , 1953, Geology of the west-central part of the Gunnison Plateau, Utah: Geol. Soc. Amer. Bull., v. 64, p. 1261-1278.

Hintze, L. F., 1962. Structure of the Southern Wasatch Mountains and vicinity, Utah: Brigham Young Univ. Geol. Studies, v. 9, pt. 1, p. 70-79.

Hunt. R. E.. 1950, The geology of the northern part of the Gunnison Plateau, Utah: unpub. Ph.D. dissertation, Ohio State Univ., 267 p.

Imlay. R. W. , 1952, Correlation of the Jurassic Formations of North Amercia, exclu- sive of Canada: Geol. Soc. Anier. Bull., v. 63, p. 953-992.

John, E. C., 1964, Petrology and petrography of the intrusive igneous rocks of the Levan area, Utah: Brigham Young Univ. Geol. Studies, v. 11, p. 67-97.

Johnson, K. D. , 1959, Structure and stratigraphy of the Mount Nebo-Salt Creek area, Southern Wasatch Mountains. Utah: Brigham Young Univ. Research Studies, Geol. Ser., v. 6, no. 6, 49 p.

Kummel, Bernhard. 1954, Triassic stratigraphy of southeastern Idaho and adjacent areas: U. S. Geol. Survev Prof. Paper 254. p. 171.

Loughlin, G. F., 1913, Reconnaissance in the Southern Wasatch Mountains, Utah: Jour. of Geol., v. 21, p. 436-452.

Metter, R. E., 1955, Geology of a part of the Southern Wasatch Mountains, Utah: unpub. Ph.D. dissertation, Ohio State Univ., 243 p.

McKee, E. D., el d, 1956, Paleotectonic maps of Jurassic System: U. S. Geol. Survey Misc. Geol. Invest. Map 1.175.

---- , 1959, Paleotectonic Maps of the Triassic System: U. S. Geol. Survey Misc. Geol. Invest. Map 1-330.

NEB0 OVERTHRUST 89

McKelvey, V. E., and others, 1956, Summary descriptions of the Phosphoria, Park City, and Shedhorn Formations in the western phosphate field: Amer Assoc. Petrol. Geol Bull.. v. 40, p. 2826-2863.

1959, The Phosphoria, Park City, and Shedhorn Formations in the western phbsphate field: U. S. Geol. Survey Prof. Paper 313-A, 47 p.

Muessig. S. J., 1951a, Geology of a part of Long Ridge, Utah, unpub. Ph.D. disserta- tlon, Ohlo State Un~v. , 213 p

---- , 1951b, Eocene vulcanism in Central Utah, Sc~ence, v. 114, p. 234. Reesrde, J B., et al, 1957, Correlation of the Trlassic Format~ons of North America,

Exclusive of Canada: Geol. Soc. Amer. Bull., v . 68, p 1451-1514. Rrchards. R. W.. and Mansfield, G . R., 1912. The Bannock overthrust: major fault

in southeastern Idaho and northeastern Utah: Jour of Geol., v. 20, p. 681-709. Sthoff, S. L., 1937, Geology of the Cedar Hrlls area, LJtah unpub. Ph.D. dissertation,

Ohio State Univ. ---- , 1951. Geology of the Cedar H ~ l l s area, I I tah Geol. Soc. Amer. Bull., v.

62. p. 619-645 Spieker. E. M . 1946. Late Mesozorc and Early Cenozoic h~story of central U t a h U.S.

Geol. Survey Prof. Paper 205-D, p. 117-161. ---- , 1949. The Transrtion between the Colorado Plateaus and the Great Basin in

central Utah: Utah Geol Soc. Guidebook to Geology of Utah, no. 4. 106 p. Thomas. H. D.. and Krueger. M. L.. 1946, Late Paleozoic and Early Mesozoic strati-

graphy of Ulnta Mountains. Utah: Amer. Assoc. Petrol. Geol. Bull.. v. 30, p. 1255- 1293.

Welsh. J . E... and James A H., 1961. Pennsylvan~an and Permian stratigraphy of the central Oqurrrh Mountarns. Litah. Utah Geol Soc. Gu~debook 16, p. 1-16.

Manuscript received August 6, 1965

B. ALLEN BLA&K - Brigham Young University Geology Studies - Volume 12 1965

EXPLANATION Setdimento r y

1

Rocks

F-]73s.. 1 Y o u n g A l l u v i u m

u A l l u v i u m U n d i v i d e d F,

Old Al luv ium

I S a l t C r e e k

Fang l o m e r a t e Y

1 Golden s Ranch F o r m a t i o n I

P r i c e R ive r F o r m a t i o n

Cretaceous-Tertiary Undivided

+

0

lnd ianola Group

L

3 Jurassic Undiv ided 7

Nugget Sandstone

( Thaynes Limestone Triassic Undiv ided I W o o d s i d e Shale --'

Franson Member

- - Meade Peak Park City and Phosphoria

Shale Tongue Formations Und iv ided

Grandeur ~ e m b e r l - Diamond Creek

Sandstone - L Kirkman L imestone T I " S.

7'. 13s.

u Oqu l r rh Format ion

Igneous Rocks - Dike l a

L Andes i te Dike

SYMBOLS

Contact dashed where a p p r o x i m a t e l y l oca ted

Base m a p en la rged f r o m U.S.G.S. Nephi, Santaquin, Sent~guia BRQ M w ~ ~ t i hpe~rapbic ok9Qk,

Geology and d r a f t i n g by B. A l l e n B l a c k 1964-65 I 1

Scale i n M i l e s

U --- d

Fault dashed where approx imate ly l o c a t e d

u, upthrown side; d, downthrown s ide lPP0

a

A A' ' ~ohnson (1959) P la te 8. sect. 8-0:

Thrust Fault dashed where approx imate ly l oca ted

b a r b s on upper p la te

7 0 Dip and St r ike of b e d s I

of over turned beds of v e r t i c a l b e d s +$ C Scale Miles C'

Ant i c l i ne a x i s approx imate ly located

(IPPo) Volcanic WaseSch cal.

Sync l ine ax is approx imate ly l oca ted

Paved Roads - Dirt Roads===, Scole Miles DI

Quarr ies X Permanent

S t r e a m s Tempora ry - - - - -

S t r e a m s

MAP GEOLOGIC THE MOUNT CREEK VICINITY,

SOUTHERN WASATCH M OUNTAINS, UTAH A p p r o x i m a t e Dec l ina t ion 16 &*