Geologic Map of the Esmeralda Hill 7.5’ Quadrangle,Lewis and Clark County and Powell County, Montana

University of Wisconsin - Eau ClaireDepartment of Geology

2010

Balgord, E.A., Mahoney, J.B., Potter, J.J., Pignotta, G.S., Wittkop, C., King, N.E., Ihinger, P.D., Hardel, B.G., and Kadulski, B.

Montana Bureau of Mines and GeologyEDMAP 8

Montana Bureau of Mines and Geology EDMAP 8

This report was prepared by geology students under the direction of their advisors as a product of the EDMAP Component of the U.S. Geological Survey National Cooperative Geologic Mapping Program, Contract Number 2007-045. It has not been reviewed by the Montana Bureau of Mines and Geology and does not neces-sarily conform to the usual style and standards for Bureau publications.

1 0 10.5

MILES

Cdc

Cf

Cm

Cp

Cpi

Cw

Jem

Kc

Kk

Mlp

Mmc

Pa

Pp

Pq

Qal

Qt

Tr

Ts

Ybo

Yh

Ym

Yms

1 0 1 20.5

KILOMETERS

±SCALE 1:24,000

CONTOUR INTERVAL : 40 FEET

Kap

Kgd

MAP SYMBOLS

Anticline

EE EE EE EEEE Dike

Road

LakeSyncline

oBedding; inclinedrBedding upsBedding overturned

¹Foliation; cleavage

ÃJoint

Contacts

Approximate

Approximate Normal Fault

( ( Approximate Thrust Fault

Covered

Covered Normal Fault

Known

(( (( (( Known Thrust Fault

Landslide Head Scarp

Breccia

2,500 0 2,500 5,0001,250

FEET Dj

Dtf

Ql

Base reproduced from 2001 Esmeralda Hill USGS topographic map2004 magnetic declination, east 15o

CORRELATION OF MAP UNITS

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ooo

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ooo

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oo

o

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oo

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soo oo oo

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Lois Lake

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EE EE EE

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46o 37’ 30”112o 22’ 30”

46o 45’112o 22’ 30”

46o 45’112o 30’

46o 37’ 30”112o 30’

Kc

Kc

Kc

Yms

Ts

Ybo

Dj

Ym

Ql

Cpi

Kgd

Mmc

Dj

Mmc

Qal

Cm

Tr

Ts

Dj

Dtf

Cdc

Cm

Cp

Qal

Mlp

Dtf

Ym

JemPq

Cpi

Cpi

Dj

Mlp

Kc

Kk

Yh

Ym

Mmc

Pa

Cw

Dj

Dj

Mlp

Cm

DtfCp

Jem

Cw

Mlp

Dtf

Kgd

Cdc

Qal

Cp

Pq

Dtf

Qal

Mlp

Qt

JemKk

Kgd

Kgd

Mlp

Kgd

Mmc

Cf

Kk

Pq

Pa

Pp

Cf

Cdc

Cw

Cf

Pp

Pa

Pa

Pp

Qt

Dtf

Kgd

Dtf

Kap

Kap

Mmc

Kap

Kap

Kap

Kap

Kap

1

2

2

8

8

8

1929

2326

12

20

1628

6036

26

2830

22

24

67

8551

45

2043

81

675648

3633

42

8584

82 44

45

34

41

60

69

76

80

20

68

3268

74

81

29

1415

19

19

47

19

37

2625

26

28

2550

45

80

13

80

82

19 33

57

46

27

49

40

70

2117

41

30

35

19

23

35

35

36

34

11

1624

25

25

29

23

34

2426

19

35

50

2321 14

24

19

33

43

11

60

16

26 31

14

14

2730

6128

55

3053

36

26

2820

24

32

28 18

15

17

12

21

14

2124

37

37

21

35

18

2432

22

18 34

15

2626

28

80

10

18

46

25

26

26

Ts

QUADRANGLE LOCATION

MONTANA

YmsYmsDj

Dj

Dj

Mmc

Mmc

Cm

Cm

Ts

Cdc

Cdc

Cm

Dtf

Ym

CpCpi

Cw

CpJem

Cw

Cw

Kgd

Kgd

KkPq

Pa

PpCdc

Cf

Cf

Cf

Kap

Kc

KcKc

Cpi

Cpi

Mlp

Mlp

Yms

Yms

Dj

Dj

Mmc Cm

Cm

Cdc

Cdc

Dtf

Dtf

Ym

Ym

Cp

Cp

Cw

Cw

Kgd

Kgd

Cf

Cf

Cpi

Cpi

MlpMlp

Ybo

Ql

2,000 m

1,750 m

1,500 m

1,000 m

500 m

-500 m

-1,000 m

2,000 m

1,750 m

1,500 m

1,000 m

500 m

-500 m

-1,000 m

2,000 m

1,750 m

1,500 m

1,000 m

500 m

-500 m

-1,000 m

2,000 m

1,750 m

1,500 m

1,000 m

500 m

-500 m

-1,000 m

DESCRIPTION OF MAP UNITS

B

A

B

A’A

B’

A’

B’

CenozoicNote: Colluvium (Holocene)—a matrix-supported diamict consisting of angular to subangular pebble and cobble sized clasts derived from local bedrock in a matrix of silt and sand—is found throughout the study area in areas of moderate and steep slope

Alluvium (Holocene): Sand, minor pebble to cobble gravel, silt, and wetland deposits in the floodplains of modern streams and drainages. Many small deposits in narrow valleys were not mapped. Up to 3 meters thick

Quaternary talus: Angular boulder, cobble and pebble-sized blocks that form coalescing aprons at the base of steep cliffs

Landslide deposit (Pleistocene?): Sediments of Ts deformed by mass movement. Recongized by hummocky surface and bounded by pronounced head scarp. Preservation of hummocks suggests late Quaternary age

Tertiary-EoceneTertiary Rhyolite Porphyry: light to medium pink, flow-banded lithic, vitric, crystal (sanadine, quartz) rhyolite tuff

Tertiary sedimentary rocks: Poorly consolidated, light tan to reddish brown, thin bedded mod-erately well-sorted, very fine to medium grained lithic (rhyolite) arenite intercalated with reddish brown siltstone and clay. May contain minor pediment gravels near surface. Poorly exposed, primarily exposed in landslide scarps

Mesozoic

Cretaceous Intrusive RocksAndesite porphyry: Dark-green to dark-gray, aphanitic to plagioclase-phyric; forms rubbley outcrops along ridges, preferentially intrudes fine grained units, forms small stocks and dikes

Intrusive rocks of the Boulder Batholith, undivided; Medium to coarse grained, equigranular to biotite, hornblende granodiorite to quartz monzonite

Cretaceous Sedimentary RocksColorado Group: Recessive, orange, brown and red thinly bedded, thin laminated fine-grained sandstone, siltstone and shale.

Kootenai Formation: Light-gray to brown, medium-bedded, moderately sorted, chert-lithic arenite; commonly displays large low-angle cross-stratification (150-350 ft (~50-100 m). 100m

Jurassic Sedimentary RocksMorrison Formation and Ellis Group, undivided: recessive succession characterized by a lower portion of thin-bedded, calcite-cemented, lithic arenite, sandy siltstone, siltstone, and shale yielding orange, red, tan, and dark-gray, sandy siltstone regolith and an upper portion of thin- to medium-bedded, locally contains up to 7 cm long belemnites, orange to red quartz arenite, thin-bedded siltstone, shale, and sandy micrite (125-225 ft (~40-70 m)). 120m

Paleozoic

Permian sedimentary rocksPhosphoria: Dk-lt gray, semi resistant chert rich, oolitic in part, thinly bedded phosphatic wackestone

Pennsylvanian sedimentary rocksQuadrant Formation: Cliff-forming unit of buff-yellow and pink, medium-thick bedded, silica-cemented, cross-stratified, quartz arenite. Locally contains chert nodules and thin calcareous silt laminations. Contains basal unit of dolomitic, cross-stratified quartz arenite to sandy dolo-mite. (150-350 ft (~50-100 m). 120m

Amsden Formation: Recessive unit of light-gray to tan, thinly laminated, thin-bedded quartz arenite, siltstone, shale, and silty micrite that produces distinctive reddish-brown regolith (100-165 ft (~30-50m)). 50m

Mississippian sedimentary rocksMadison Group:

Mission Canyon Formation: Thick to massively bedded, medium- to dark-gray, fossiliferous (rugose corals, sponges, and bioclastic hash) wackestone, packstone and locally rudstone. Displays characteristic scalloped surface and locally abundant thin, dark-gray chert nodules, local medium-thickly bedded trough cross bedded crinoids. Coarsely crystalline in part. Mas-sive character commonly makes determination of bedding orientation difficult. (575-825 ft (~175-250 m)). 425m

Lodgepole Formation: Characteristically very well bedded, thin- to medium-bedded micrite to packstone with tan silty interbeds. Displays abundant sedimentary structures including scour marks, graded bedding, parallel laminations, cross lamination, and ripple marks. Forms blocky outcrops. Becomes thicker-bedded and increasingly fossiliferous (crinoids, brachiopods, rugose corals, bioclastic hash) toward gradational contact with overlying strata (500-650 ft (~150-200 m)). 200m

Mississippian-Devonian sedimentary rocksThree Forks Formation: Recessive unit of gray to green, thin-bedded, calcareous, micaceous shale, siltstone, silty micrite, and lesser fine-grained quartz arenite. Subdivided into three members consisting of a middle resistant, platy, thinly laminated siltstone, silty micrite and fine-grained sandstone overlain and underlain by recessive siltstone and shale units. Charac-terized by reddish-orange to green, platy regolith (165-250 ft (~50-75 m)). 200m

Jefferson Formation: Dark-gray to blue-gray, medium- to thick-bedded, locally massive, inter-calated dolomite (duotone) and subordinate limestone. Consists of a resistant basal medium-bedded, dark-gray, fossiliferous (crinoids, brachiopods, corals) sandy dolomitic wackestone with strong fetid odor overlain by a recessive black, calcareous shale. Upper section is a cliff-forming, slightly fetid, locally fossiliferous sandy dolomitic wackestone with thin sandstone laminations. Unit is distinctly sucrosic and weathers to a light-gray scalloped surface (500-650 ft (~150-200 m)). 550m

Cambrian sedimentary rocks Dry Creek Formation: Orange, red, brown, and yellow, thin-bedded, thinly laminated siltstone and shale with subordinate very fine grained quartz arenite. Contains abundant parallel lami-nae, cross-laminae, and climbing ripple laminae. Weathers recessively and forms valleys and saddles characterized by reddish, platy regolith (60-150 ft (20-50 m)) 200m.

Pilgrim Formation: Lower portion characterized by a grey to light grey thin convolute bedded, mottled micrite interbedded with orange weathering fine grained quartz arenite. Grades into a dark grey, med-thin bedded, bioturbated dolo-wackestone overlain by a resistant, fetid, heavily bioturbated with calcite vugs, dolomitic wackestone (~500 ft (~150m)). 340m

Park Formation: Recessive unit of green-grey, thinly laminated, locally calcareous micaceous shale that produces distinct green regolith (~150-165 ft. (50m)). 70m

Meagher Formation: Medium grey, fossiliferous wackestone to micrite containing very thin wavy sandy interbeds which grades into a thinly bedded, light tan to dark grey, locally mottled, sandy micrite to packstone. Upper portion is light grey to grey, thin-medium bedded, locally cross-stratified oolitic packstone (120-140 ft (~40m)).

Wolsey Formation: Recessive unit of tan, parallel laminated, thinly bedded micaceous sandy shale/siltstone to very fine quartz arenite. Characterized by tan micaceous regolith (200-220 ft (~65m)).

Flathead Formation: Poorly exposed, only visible in float, light tan to pink, moderately sorted, medium to thick bedded, parallel and cross-stratified, siliciously cemented subfeldspathic arenite to quartz pebble conglomerate that fines upward into thin to medium bedded, trough to planar cross-stratified quartz arenite (50-100 ft (~15-30m)).

Proterozoic sedimentary rocksMiddle Proterozoic Belt Supergroup:

Characterized by red, green, and tan, thin bedded siltstone and shale interbedded with tan, fine to medium grained, thin to medium bedded, quartz arenite to micaceous subfeldspathic arenite and green-grey, fine grained calcareous arenite (>5000? ft (>1500? m)).

McNamara Formation: Medium-brick red, very recessive, thinly bedded, contains low angle cross stratification, climbing ripple cross stratification, abundant rip up clasts, medium grained, moderately to well sorted, interbedded with red argillaceous shale, arkosic arenite

Bonner Formation: Distinctly cliff forming, med pinkish-red to whitish tan, thickly bedded, locally contains red mud rip-ups, med-coarse grained, with arkos and quartz pebbles, moderately to poorly sorted, subangular-angular, trough cross stratified, feldspathic arentite

Mount Shields Formation: Med-red to lt-tan , parallel and trough cross laminated, fine-med grained, thin-med bedded subfeldspathic arenite with interbedded red argillite

Helena Formation: Lt-med blue, microlaminated, recessive, locally contains ripple marks and mud rip-ups, interbedded siltstone and dolomicrite