LIFORNIAGEOLOGY

. ;

SEPTEMBER 1990

Petrified Forest

A PU8UCAllOH Of TllEDE'PARTIIEHT Of CONSER'tAnoH

orviSIOH Of IIIHES AND GEOlOGY

GEORGE DEUKMEJIAN"'-~

T"'RMourCM~ GOROONK VANVLECKSecretary lot RasOUTces

DI\lIlrlmenl 01 ConsenralJOn RANDALL M WARDo.tector

O,v,akInol MI ...s& Geology JAMESF DAVISSI81e GooIog'!I

In This Issue ISOUTH COAST GEOLOOICAL SOCIETY FIELD TRIP 194CALIFORNIA'S FOSSIL FOREST 195SELF·GUIDED GEOlOOIC TOUR IN JOSHUA TREE

NATIONAL MONUMENT 203MINERAL CROSSWORD PUZZlE 213JOHN WOLFE RETIRES , 214ALFRED O. WOODFORD MEMORIAL 214ANSWERS TO MINERAL CROSSWORD PUZZLE 214NWWA GROUNDWATER SEMINARS 215MAIL ORDER FORM .. ,........................ . , 215CALIFORNIA JOURNAL OF MINES AND GEOLOGy 216CALIFORNIA GEOLOOY SUBSCRIPTION FORM 216

CALIFORNIA GEOLOGY staU

EdftOl·ln·CIlIeI:

Grapllocs and Oesogn:

PubioeatlOf\s SUpefVI$Ol':

Don Dupias

LouISe Huckaby

Jell Tamberl

Cover: Circa 1870 photo of a fossilized tree trunk In the Petrified Forest, SonomaCounty. northern CaJilornia Coast Ranges. This parlt. has been a popular ttlUnstattraction Since the 18OOs. ·Petrified CharUe: the onginal owner of the PetrifiedForest is to the back and nght olthe log with illS pet goat. Remains of severalwell·preserved fOSSIlIZed redwood Irees that were buned by volcaniC debrisdunng the PlIOCene Epoctl have been unearthed and are on display in thePetnfied FOl"est An artlde aboul th,s par1l. starts on page 195. Photo by Taber.counesy 01 the Les Youngs Photo CollectIon.

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~ end lntclrn\aIo:In Offic.NO Ben;ut 0.-, SKt_. CA 9Yle-0131CAliFORHtA GEOl.QGYPutIIIC:~. 916-....5-5716

t.o. AtIgeln orr;c. 107 South 8r00dw~, Room 1065,t.o. MgiIoIn. CA90012..u02lTeIepfIorIe 213·620-3560)

1"lnMrlI .... 0I1a 380C<w; Or.... Su,I. 100.PIN..., HIll. CA !M!i23-1921(Telep/lOtle "'15-646-5920)

CAUFOANIA GEOl.OGV (ISSN 0026 4555) It pullIoINIdI'rI041H'Ily b~ IN Depattmenl 01 Conse,v.llOn. O'V'SIOO 01M..... Ind Geology. The Records 0I10:e i. II 1721·2OlhS"..,. SI~'lmenlo. CA 95814 second cI••1 POS'agI"~lld II SI~rll'MlnIO.CA. POSlml.le, Send Idd'I"cn.ngelto CAUFORNIA GEOLOGY (USPS 350 &CD).eo. 2980. sacrlmento. CA 95812-2980

RepOfl.l ~onc"twIg 0,_ 01 M.nn Ind GeologyprQIIClI aflClarlodea end__....Itd to lhl ... lh_In Ceh/otnIa. are W;:Iuded in lNI megu..... eo...1I'0Iltdlfbf;les phologtaphs.__.aflCl~-.nu__

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THECOHClUSlOf\lSAHDoPlN~SEXPRESSED INARTIClES ARE SOlELY THOSE Of THE AUTHORSAND ARE NOT NECESSARILY ENDORSEO 8Y THEDEPARTMeNT OF (X)fISERVATlOH

COtluporwHnn .houk! be add.eul'd 10 Edllor,CAUFOfU"lA GEo..OGV, ll«Illetcul 0t'Ne. Saa_,CA~1"'-o131

s..tIIa..,._ $10 00 PI< yHt SongIe <;:Opel $1 251ICft. Send~ ........ end-. 01 acldtw1I....malOltoCAl.lFORHlA GEOl.QGY. PO Elm 2980.~. CA 95812-2980

Seplembel' 199ONoIume 44/Number 9

CGEOA 44 (9) 193·216 (1990)

I Announcement ISouth Coast Geological

Society Field Trip

The South Coast Geological Society ishosling a flekl trip to the Colorado Exten­sional Terra,n and Whipple Mountains ofsoutheastern C31ifomia The trip wiD be ledby Greg Davis on October 26. 27. and 28.1990. Reg~1ion information and furtherdetails are cwailable by writing

Sooth~ Geological Societyclo John FosterDepartment of~ Sciences..MH263DCalifornia State Univers,tyFullerton. CA 92025or caB, (714)449-7096 ~

'" CALIFORNIA GEOLOGY SEPTEMBER 1990

California's Fossil ForestSonoma County

By

ELISE MATTISON, GeologistDivision of Mines and Geology, Sacramento

Geyserville

Franz ValleyRoad

PetrifiedForestRoad Sl. Helena

JCalistogaRoad 29

0 ,I ,

Miles

PetrifiedForest

Mark WastSprings

Road

SANTA

Figure I lOCOT'on maps 01 1M Pelrilie<! Fore.1.

There ore over 5,100 notive ~pede. ofpion!! in Coli/ornia-more Ipeeie. thon in anyother .tole. Thi. ,tote i. fortunote to hove suchdiversity ....here dimDle, geology, geography,ond the force. of evolution combine to form"variety of pflysicolenvi,onments. The 1I0roihistory of California 'pOnl ten. of million. ofyear•. Fo•• il remains of plonh provide in,ightinlO how the environment, lond.cope. and li/"in on<:e,I,gl Coliloroio changed over geologic'ime, Thi. article describe. one of the finure~omp'el of" Pliocene perrilted fore,l in theworld. Thi. oncient fore,t i, located in theno,thern Coliloroio COOl! Roog,,' ond ho.been 0 populo, lou".' olt,oclion "nee 'heI BOO•. Vi,i'on 10 lhe Pel,ilied Fo,est conenvi.oge lor them.elve. how moje"ie,edwood Irees once lo,esred this oreomo,e Ihon J million yeo.. ogo . editor.

!•

I

SAN FRANCISCO

o 10

Miles

INTRODUCTION

P eriods of intense volcanic activity characterized theregion northeast of San Francisco Bay during the

Pliocene Epoch. During periods of volcanic quiescencesoils formed, forests grew. and now extinct zebra-likehorses. hyena-like dogs. and giant tortoises roamed theregion (Stirton. 1951). This area had a cooler and moremoist climate than it does today. Here. an ancestralforest was felled and buried in volcanic ash almost threeand a half million years ago. This well preservedpetrified forest is a rare example of Pliocene flora inCalifornia.

The fossilized forest was reportedly discovered in the1850s (Hoover. 1937) but lay undisturbed until 1871when Charles Evans found the fossilized trees and beganexcavating them from their hardened volcanic ash en­casement. Petrified wood was found scattered along astrip of land 17 miles long by one mile wide on the west­ern side of the ridge that defines the Napa/SonomaCounty line in the vicinity of Calistoga (Caton, 1873).Today a part of this strip of land is a privately ownedpark (Petrified Forest) where visitors can see the re­mains of an ancient redwood forest (Figure 1).

CALIFORNIA GEOLOGY SEPTEMBER 1990 '"

F't.oto 2 lJrM;orthtng _ follill_ In 1930 Excovohng ....... fo..illree...(ltd.-.~ becou~ rhe YOkonic: o~ matrix hoI hardened 10 sollCl .oek1'f>oIo (DUtIes,. 01 If.. '.",',«1 f ..esl Mu_

•PhoIo 1 Sleoeopt.o!o 01_ oIlhe rrees in the Perr,F;ed Forl!l.l, c;reo 1870sPeI,iloed Fottil ....~Ion p<»e wlm Perrilted Chorlie, who ~1s 10 lhe "gll!"";!hhi, pel goot bes~ hIm. Sle<eophoto. __ populor during the !ole 1800sonc! eorly 190Ch They ore mode by JokIng two pholographs 01 ,lightlydifferent angles onc! plcxirog r+.em.ide by.ide When Ylewed precisely, thebra,n combin.u the two photo. 10 produce 0 tIlr_dimensionai image !hotappean life·lik. Normolly, s*eophoto. are viewed wim 0 stereoscope. whichtonsish oIlWO rnognifying len5el "I' in a loIdillQ metol frame HoweYI!r, it i.pouib!e wim prOd'C' to view thi. kind 01 photo poir "llleoKopicolly wimourrhe u'<l of a .lereoKope

Look lor w.reroll«ond. at (I dilron! objed, tl,en I>oId the well illuminatedstereophoto in your line 01 ",iew Ch.oo~ on greo in the photo tho, contrOl1swith ItI .,mounding, ond "ore inten~y. The three dimensionol image wil! beblurred or li"I, !wI olter (I .!Io'l while it should come into foeu•. Photo byrober. courtesy of the I". Youngs Pharo COI/KrjOn

HISTORICAL DEVELOPMENT

Charles Evans began excavations of the partially ex­posed fossil trees in 1871 and was soon charging visitors50 cents to see the unearthed logs (Photo 1). Known alsoas Charles Edwards and Charles Peterson. he was popu­larly dubbed "PetrifIed Charlie." His Petrified Forest be­came a tourist attraction luring people from nearby Calis­toga Springs. a popular hot springs resort. Among thesevisitors was the noted author Robert Louis Stevenson who.by 1890. had immortalized Petrified Charlie in The Sil­verado Squatlers (Stevenson. 1974):

-The proprietor was a brave old white-faced Swede.He had wandered this way. Heaven knows how. andtaken up his acres-I forget how many years ago-ol/alone. benl double with sciatica. and with six bits in hispocker and an axe upon his shoulder. Long. uselessyears of seafaring had thus discharged him at the end.penniless and sick. Withouf doubt he had cried his luckat Ihe diggings. and gol no good from thaI: withoutdoubl he had loved the boll/e. and lived the life of Jack

•,

". CAUfORNlA GEOLOGY SEPTEMBER 1990

"l1li Photo 3 Excoyoting the "Monarch" Of "TunnelTlee" (note mon wOfking ot the for end of thetunnel). The exposed length 01 thil log is obout100 f.....l, only (Ibo<"t holl 01 the eltilTl(lted totollength pholo courtesy of Ihe Pelrified ForestMuseum

Photo 4 Museum ond nolure Slore in the Ollie8ock.. house tOOl W(IS built in 1915

...ashore. Bur or the end of rhese ad·venlures. here he came: and. Iheplace hilling his fancy. down he satto make a new life of iI. far fromcrimps and rhe salt sea. ~

Asked by Stevenson if he was sur­prised at finding the petrified wood onhis land. Charlie replied:

~ 'Surprised? No! Whar wouldI be surprised about? What did Iknow about perrifactlons-followingthe sea? Perrlfacrion! There was nosuch word in my language! f knewabout putrefaction. though! fthought II was a slone: and sowould you, if you was cleaning uppasture. .~

The Hand-Book of CalistogaSprings. or, Lirtle Geysers. publishedin 1871. briefly describes the PetrifiedForest and includes a detailed articleon Ihe same subject by Yale CollegeProfessor. O. C. Marsh (Anonymous,18711.

In the book. An lIIustrared Historyof Sonoma County, California. pub­lished in 1889, an unknown authorsummarizes the declarations of thou­sands of visitors to the Forest who·pronounced il not only one of thegreat wonders of the world. but 'oneof the prettiest places' in the hills ofCalifornia'" This account gives in­structions for reaching the site bystagecoach and concludes: ~No East-

ern or European tourist can truly saythat he 'has done Califomia' unless hehas seen the Petrified Forest M (Anony­mous, 1889).

The Petrified Forest changed owner­ship several times after Petrified Char­lie sold it around 1880. Ollie Bockeepurchased the property in about 1910and she immediately began further ex­cavations to uncover some of the par­tially buried trees (Photo 2). A tunnelwas dug to expose the trunk of a fossilredwood Ihat julled from a hillside{Photo 3}. The tree was found to havea partial length of over 100 feel.Bockee donated a 5.560-pound petri­fied log to New York City. shipping itvia the Panama Canal (Anonymous,1953). She improved her properly by

building an eight room house and asouvenir shop, and by installing tele­phone lines (Photo 4). The park con­tinued to grow in popularity.

In 1951 Jeanette Hawthorne inher­ited the Petrified Forest and installed acoffee shop and picnic grounds. ThefollOWing year over 23.000 peoplefrom all over the world visited thepark (Anonymous. 1953).

The Petrified Forest today is ill

popular tourist attraction where visi­tors can observe for themselves theenormous preserved trunks of ancienttrees and contemplate what this areamust have looked like when thesegiant redwood trees were alive (Photos5 and 6l.

CAltFOfINtA GEOlOGY SEPTEMBER 1990 '"

Photo 5. 5e<:tion of fossilized ,ed""ood t'ee in the Petrified Fore,t, author fa, ":01". The'" t,ee, oreso ""ell preoerved that ..:ienti," ""ere readily able to identify them a, Sequoia langsdorlji. Same ofthe fossilized ,ed""ood t,ee, in the pork ""ere over 2,000 yeor. aid ""hen they ""ere buried

Fossil remains of 17 other plantspecies were also discovered in thelocality of the Petrified Forest. Themost common of these species include/lex sonomensis (holly), Persea cool,ingensis (an avocado tree), Pseu'dotsuga sonomensis (similar to theDouglas fir). and Quercus bockeeiand Quercus lakevillensis (oak trees)(Axelrod, 1944).

The Petrified Forest lies at an eleva­tion of approximately 900 feel. Dur­ing the Pliocene this forest grew at anelevation at least 500 feet lower thanwhere it is today (Axelrod, 1944).Subsequent regional tectonic upliftraised the fossil forest to its presentelevation. Lower elevation plants inthis area today include oaks andgrasses that can survive in the hot.dry summers of Sonoma County,

PALEOBOTANY

The Petrified Forest of Sonoma County was the subjectof the first scientific publication describing and identifyingPliocene plants of western North America (Marsh, 1871:Chaney, 1944). Tertiary plants, except for those of thePliocene. are well represented in the fossil record of NorthAmerica. The relative lack of fossil vegetation from thePliocene in western North America indicates thai majorclimatic and topographic changes resulted in conditionsthat were less favorable for abundant plant growth andpreservation (Chaney. 1944).

Fossil remains of several redwood trees are exposed atthe park. These trees are identified as Sequoia langsdorfii.an extinct species closely related to the present day coastalredwood, Sequoia sempervirens, Sequoia forests are pres­ently restricted to areas of moist climate in California andOregon. Fifty million years ago extensive redwood forestsgrew as far north as Alaska. Other Tertiary fossil redwoodsare found in numerous locales throughout the NorthernHemisphere including Greenland, Siberia. Manchuria,Europe, and the eastern United States (Chaney. 1934).

In addition to the fossilized redwood trees found in thePetrified Forest. the abundance of another evergreen tree.Abies sonomensis (an ancestral equivalent of the lowlandfir) and of a type of red huckleberry tree, Vaccinium son·omensis, indicates that a cooler, more moist climate ex­isted in this region during the Pliocene.

photo 6. A fossilized ,ed""ood t,ee named 'Oueen of the Fa,e.t" i. about '"feet in diamete' At the far end on oak tree ha, grQW'n belYieen .octian. ofthis fractured fossilized log Photo courtesy of Ihe PelrjFi,.J Foresl Museum

'" CALIFORNIA GEOLOGY SEPTEMBER 1990

EARLY INTERPRETATION

How did the Petrified Forest come to be as it is today?Since its discovery several hypolheses have been advanced10 account for the origin of the Petrified Fares!. All ofthese various hypotheses suggest that volcanic forces wereresponsible for the preservation of this ancient grove.

", .. The visitor. however learned.can only gaze in puzzled silence.and admit his inability to penetrateinto the mysteries of the remotepost. .. "

One embellished account in the Hand-Book of Colis·logo Springs. or. Uttle Geysers offers Ihis version (Anony­mous. 1871);

-Much has been written concerning the origin of thewonderful forest. which (for want of a beller theory' mayhave been submerged in distanl ages. by rhe eruplions ofsome volcano, ... which. discharging warer and ashes.couered all this pori of Ihe country. flowing ouer the lollforesls and sealing them In an eternal tomb. The ero­sion of counlless cenluries gradually exhumed and leftthem in Iheir original form. but turned 10 Slone - everyIrunk and branch remaining as 01 the lime of Ihe cOlas·Iraphe. BUI il Is nOI here proposed 10 inflici any crudespeculations upon the reader. &ientific research isbaffled in its attempls to explain this marvel of nature.The lJisitor. howelJer learned. can only gaze in puzzledsilence. and admit his inability to penetrate into Ihemysteries of the remote post.·

AnOlher author was nOI al all baffled and offers this mal­ter-of-faci accounl in Ihe following narralive (Benson.19301,

"How it got Ihere is simple. First. there was a sudden.lJio/ent mOlJement of the earth from north 10 south-omOlJement so sudden that it snapped off elJen these bigIrees at Ihe ground and hurled their tops toward thenorlh. ElJery tree Ihal fell pain IS In the same direction.Then a tremendous IJO/canic explosion blew off the topof MI. SainI Helena and cOlJered the fallen forest withIJOlcanic ashes. The healJY California rains seepedthrough Ihe ashes. rotting the wood. As the trees rot­ted. silica washed in to toke the place of the wood. Inlime. silica replaced 0/1 of the wood and formed petri­fied trees.•

The Calislogan. a local newspaper. published thisscenario (Mack. 1930);

·One is so impressed with all these sights Ihat ilseems as If one Is standing on some eminence afar offand sees thor towering mountain in Its rage. as Iterupted all that lavo, 01/ that rock; as it shook the sur­rounding territory for miles. as these gianls. tremblingin the fastness of Iheir deep-sel rOOIS. swayed. quivered.

/'holo 7. The Petrified forest Rood cuts through 0 oection of the SonomoVolconiC1 0 lew miles WilSt 01 the Petrilied forest lnole the author at thebollom l.fI/or scol.l The Pliocene Sonorno Vokonics is a roc~ un,'composed 01 a serl.S ollo~o flaw" tull. and broccio beds rhot ore locollyinterbedded wtth alluyial conglomerate, sandstone ond gro~el beds Thisroc~ unit dominates the Sanamo, Moyacmo. and Howell mounlo,n, ondca~en O\Ier 350 Kju<lre miles fram the Petaluma,Coloti lowlond eo,lwordto lhe Howell Movnloin, ond fram Suisun Soy north beyond Mt. 51 HelenoMt St Helena is a prom,nent peo~ about 7 miles northeost oflhe PetrifiedFore.t It is nat 0 .olcono In,teod, " is composed 01 folded ond erodedrocks 01 the Sanomo VolcaniC1

then gave way to fall with a deafening crash 10 be buriedby the dust and the debris of ages and to lie there. whilelater came again the plenteous rains Ihot quenched Ihefires. cooled Ihe hot lava, and penetrating down throughthe scoria. reached and embalmed the giant forms for­ever through the chemical changes that rook place whenwaler mixed with IJOlcanic ash. What a scene: whal adesolation of devastation; nothing could haue lived ifthrough: nOlhing did. ~

SONOMA VOLCANICS

The exposed fossil trees of the Pelrified Foresl lie nearthe base of the upper member of a thick stratigraphic se­quence called the Sonoma Volcanics (Photo 7: Fox. 1983).This sequence consists of a thick accumulation of basaltic.andesilic. and rhyolilic lava and ash flows. pyroclastic tuffs.

CALJFOANIA GEOI.OOY SEPTEMBER 1990 ",

and diatomaceous sediments (Kunkel and Upson. 1960)that extend over 350 square miles in Sonoma and Napacounties.

The volcanic tuff sequence in the Petrified Forest hasbeen radiometrically dated at 3.4 million years (Everndenand James. 1964). In the area of the park this tuff lies un­conformably on top of Mesozoic Franciscan Complex rocks(Fox and others. 1973). Elsewhere. the Sonoma Volcanicsunit lies unconformably above Cretaceous and Tertiaryrocks, and below Quaternary rocks. The Sonoma Volcanicsare interbedded with the Pliocene marine Wilson GroveFormation to the west, and rarely the Pliocene terrestrialTehama Formation to the east (Taliaferro. 1951).

The Sonoma Volcanics accumulated over a period ofabout ten million years (Howard. 1979). This volcanic ac­tivity created thick sequences of lava. pumice. and ash thatblanketed the region. Erosive processes carved through thevolcanic layers and created an eroded and rugged terrain.Some unconsolidated volcanic ash. saturated with rain­water. turned to mud and flowed down slope. Silica in solu­tion was leached from the volcanic debris and emptied intolakes and swamps. This created an environment favorablefor the proliferation of diatoms. Trees of the Petrified For­est flourished in soils that formed during periods of volcanicdormancy. This ancient forest was buried by subsequenteruptions. At the close of this period of volcanic activity, afinal sequence of rhyolitic lava, ash. and pumice completedthe Sonoma Volcanics unit.

Mud Flow or Lava Flow?

One popularly accepted hypothesis suggests that follow·ing a period of intense volcanic venting in this region, peri­ods of heavy rainfall converted loose volcanic ash into vis­cous torrents of mud that flowed from the northeast to thesouthwest. toward the living redwood forest. The force ofa raging mud flow (lahar) may have toppled the huge red­woods (Howard. 1979). Subsequent volcanic ash-falls bur­ied the trees. Erosional processes eventually stripped awaythick sections of volcanic rock and partially exposed someof the fossilized Jogs.

From field evidence it appears unlikely that the treeswere swept down by either a lahar or by a nuee ardente (aviolent gas-charged Java flow similar to the explosive erup­tion at MI. 51. Helens, Washington in 1980). Unbrokenglass shards. and fossilized leaves preserved in curled andtwisted forms. have been discovered in the volcanic ash ofthe Petrified Forest (Dorl, 1933). Had they been sweptaway by a flow, the shards would likely have broken andthe leaves flattened or disintegrated. Moreover. bark re­mained allached to the trees which would not be expectedhad the trees been transported a great distance. or had agreat volume 01 abrasive volcanic mud flowed over them(Photo 8).

CALIFORNIA GEOLOGY

photo 8. Close-up 01 beige-colored redwood tree bark replaced by silico.MOS1 01 rhe rrees in rhe pork were preserved wirh rheir bark intocr,

Volcanic Blast?

Another plausible hypothesis for the origin of the Petri­fied Forest is that the forest was leveled by a volcanic blastand was subsequently buried by volcanic debris, The 1980eruption of Mt. St. Helens in Washington blasted treesdown into a radial pattern with their tops pointing awayfrom the volcanic vent (R. Hoblit!. personal communica­tion. 1990).

Detailed investigations revealed that the trees in the Pet­rified Forest in Sonoma County point. on average. betweenN35°E and N45°E; others point slightly west of north oralmost directly east-west (Dorl. 1933). This may indicatethat a sudden volcanic outburst. similar to that which oc­curred at Mt. 51. Helens, leveled the trees or it may merelyreflect the orientations of the slopes on which the treesgrew. fell. and were buried more than three million yearsago.

SEPTEMBER 1990

It is generally believed that the volcanic ash that buriedthe Petrified Forest emanated from the northeast. in thegeneral direction the tree roots point. Many tourists andscientists alike have assumed that Mt. 51. Helena. a localpeak to the northeast of the Petrified Forest, was thesource of the volcanic eruptive debris that buried the trees.Me. St. Helena is not a volcano. Rather. it is composed ofa number of volcanic flows that have been uplifted. folded.and eroded (Bowen. 1951). Locating the actual eruptivecenters may be impossible because geologic procesSeShave drastically changed the terrain in this region since thePliocene.

Separate Volcanic Events?

Another hypothesis advances the opinion that the treesin the Petrified Forest were buried by more than oneevent. The author of the book. An lIIus/rated History ofSonoma County. published in 1889, reported that thetrees are exposed in two tiers. This hypothesis wasstrengthened by another researcher who described someof the petrified trees lying 20 vertical feel above anotherlayer of trees (Dorf. 1933). If this multi-event hypothesisis correct. such an irregular strata position may have re­sulted from separate volcanic events. burying first one gen­eration of trees, then another many years laler. This hy­pothesis is supported by the existence of varied types ofvolcanic ash covering the petrified trees (Dor!. 1933). If alltrees had been buried during a single event. the ash wouldlikely be of a more uniform lithology.

PETRIFICATION

The preservation of the trees of the Petrified Forest isdue to a process called petrifaction. from the Latin. ··turn­ing to stone." where the structure of the wood is retainedeven at the cellular level. Rhyolitic volcanic ash. high insilica content. is a matrix material commonly associatedwith fossil trees. Over many years. silica in solution infil­trates the wood and gradually replaces the organic compo­nents. preserving them in structural detail. Most of the pet­rified wood of Sonoma County is beige or light brown. Af­ter millions of years the bark and wood grain remain re­markably well defined (Photo 9).

The Petrified Forest Trail

1. Parking Area2. Museum and Nature Store3. 'The Pit Pine Tree" (redwood)4. 'The Gully Tree'5. 'The Petrified Woodpile"6. "The Giant"7. "The Queen of the Farest"a. 'The Monarch" or "Tunnel Tree"9. • Rocks of Ages'10. "The Robert louis Stevenson Tree"1 1. Rest Rooms

photo 9. Detail of fossilized wood groin from the Petrified Fore.t inSonoma County. The trees were quickly buried (which prevented decoy)and remained undi,turbed for millions of yeors while alteration processe,pre,e",ed the groin of the wood. 5ili<;0 in 'Olution leached from thesurrounding yokonic ash. permeated the wood, and slowly replaced theorganic material so perfectly that it i. po..ible to see the annual growthrings, and even the individual cells under a microscope,

0 G) ® ®®

®@)

®

® @ "i-t

CDMap .howing lhe trail wilh locations of fossilized redwood tree,.Their 'popularized" nome. are ,hown to the left.

CALIfORNIA GEOLOGY SEPTEM8ER 1990 '"

The entrance to the Petrified Forestis off of Petrified Forest Road, ap­proximately four miles west of Calis­toga (Figure L Photo 10). Visitorswalk a shady 1I4-mile-long loop trailwhich leads to at least seven exposedpetrified tree trunks measuring up toeight feet in diameter. Oaks,madrones. bay trees and other repre­sentatives of the living forest are alsomarked. The trail ends at a gift shopand museum.

The park is open to the publicfrom 10;00 a.m. to 6;00 p.m.during the summer. Winter hoursare 10;00 a.m. to 5:00 p.m. Gen­eral admission is $3.00. with dis­counts for seniors and children.Reservations for group tours canbe made by telephone. For fur­ther information call (707) 942­6667 or write to Petrified Forest,4100 Petrified Forest Road, Calis­toga, CA 94515.

photo 10. Enlronce to lhe Petrified Fore.l, Coli'logo, Colifornia, View i. to the north from thePetrified Forest Road rhol runs between ColislOgo and Sonro Row (see Figure'). The parle il>Cludesrest rooms, parking, and picnic focilities The Pelrified foresr is registered o. Colifornio Hi.loricollandmorle .915. In conlrost to the fossilized redwood trees of the Petrified Foresr, tre." living in theparlc today include bloclc ook, coastol oak, white oak, volley oak, modrone, ond Douglo.lir.

REFERENCES

Anonymous, 1871. Hand·book of CalistogaSpnngs. or. lillie Geysers: Alta CaliforniaBook and Job Printing House. San Fran·CISCO. California, 30 p.

Anonymous, 1889. An illuslrated hislOry of Son­oma County, California: Lews PubllshmgCompany. 737 p.

Anonymous. 1953. The tale of lhe PetriliedForest 01 Calltornia: published by PelnliedForest, Sanla Rosa, Calilorf1la. 36 p.

A~elrod, D. I.. 1944. The Sonoma tlora InChaney. A. W, editor, Pliocene 1I0ras 01CalifornIa and Oregon: Carnegie lnstllu!ionof Washington Publlcalion 553. p. 167-206,

Benson. A. L.. 1930, A gIrl who saw a fortune indead trees: Psychology MagaZine. Septem·ber issue. p. 26·29.

Bowen, O. E. Jr.. 1951. Highways and bywaysof particuiar geologic interest In Jenkins. 0P . editOr. Geologic Guidebook ot the SanFranCISco Bay counties: California D,v,sion01 Mmes Bulletm 154. p. 315·379.

Caton. J. D.. 1873. The Pelnfled Foresl of Call·lor",a - leller 10 lhe Chica90 Tribune, Au­gust 17. In Caton, J. D.. 1880, Miscellanies:Houghton. Osgood. and Company. p. 348·354.

Chaney. R W.. 1934. Redwoods of the past:Save-the·Redwoods League, 7 p

Chaney, R W.. 1944. Introduction, Chaney, RW, edItor, Pliocene !loras ot CalifornIa andOregOJ'l: Carnegie InstItution 01 WaShIngton,Publlcallon 553, p. 1-20.

Dor1. E" 1933, Pliocene 1I0ras ot Calltorflla,Dort, E. and Webber. I. E.. Slud,es 01 thePliocene paleobotany ot California: CarnegIeInstitution of Washington PublicallOn 412,p. 1-112.

Evernden. J F" and James. G. T , 1964, Potas­Slum·argon dates and the Teniary tloras 01North Amenca; American Journal of Sci­ence. v. 262, p. 945-974

Fo~. K. F. Jf.. 1983, Tecton,c selliOg 01 lateMIocene, Pliocene, and PleIstocene rocks In

pall 01 the Coast Ranges north of San Fran·CISCO, CalIfornia: U.S. GeologIcal SurveyProhlsslonal Paper 1239,33 p.

Fo~, K F. Jr, Sims. J. D.. Bartow, J. A., andHelley, E, J.,1973, PrelimInary geologic mapot eastern Sonoma County and weSlernNapa Counly, Caillornia: U.S GeologIcalSurvey Field Studies Map MF-483

Hoover, M B" 1937, HiSlonc spots In Cal.lor­",a, counties of the Coasl Range volume:StaJ'ltord Un,verSlty Press. 718 p.

Howard. A.D, 1979, GeologIC hiStory 01 mIddleCahlornla: UniverSity 01 California Press,p.61.

Kunkel, F. and Upson, J. E., 1960. Geology andgroundwater in Napa and Sonoma valleys.Napa and Sonoma counlles. Calltornia:U. S. Geologic Survey Waler Supply Paper1495.252 p.

Mack, I., 1930. Was petrified by volca",c ashesin centunes past: CallSl0gan. June 20.1930.p. 1.

Marsh, O. C., 1871, NOllce of a fOSSIl 10reSl In

the TertIary 01 Callfor",a: American Journalof Science and Arts, v. 1, p. 266·268

Stevenson, A. l .. 1974, The silverado squaUers:SIlverado Museum, S1. Helena. Caillorn,a,115 p.

St<rton, R. A.. 1951, Prehlstonc land anImals 01the San FranCISCO Bay regIon in JenkinS, O.p.. ed'lor, GeologIC Guidebook ot the SanFrancisco Bay countIes: California D,v,s,on 01Mines Bulletin 154. p. 177_186.

Taliaferro. N L.. 1951. Geology of lhe San Fran·cisco Bay counties in JeJ'lklns. O. P., ednor,Geologic guidebook of the San FrancrscoBay countIes: California DJVlsion of MinesBulletIn 154, p. 117-150. ~

202 CALIFORNIA GEOLOGY SEPTEMBER 1990

Self-Guided Geologic Tour inJoshua Tree National Monument

Riverside County. California

By

DON DUPRAS, GeologistDivision of Mines and Geology

Joshua Tree National Monument is apopular southern California tourist attrac­tion, II is also a lavored area to teach be­ginning earth science students about geo­logic processes. The Geology Tour Roadlog in this article is adapted Irom an eightpage self·guided tour brochure titled Geol­ogy And Man (Wanrow. 1975), and is re­printed in part with permission of the authorand the National Park Service. This bro­chure can be purchased for $0.25 atMonument Visitor Centers.... editor.

INTRODUCTION

J oshua Tree National Monument wasestablished in 1936 and contains

870 square miles. most of which is highdesert. The Monument encompassessome of the most interesting desert geo­morphic features in California. Ruggedmountains. prominently exposed graniticmonoliths. and exposed fault scarps re­veal how geologic processes shaped.and continue to shape. this stark desertlandscape (Photos 1 and 2). Much ofthe Monument is above 4.000 feet andsteep mountain escarpments border thisregion to the north and south. TheMonument is located about 140 mileseast of Los Angeles and is accessible byhighway from the north and from thesouth (Figure 1).

Photo 2. Southward view illustrating typicalexposures of rounded and jointed White ....Tank monzonite in the Monument. Photo ....courtesy of the National Park Service.

Photo 1. View to the northeast along the main Monument road at Covington Flats showingoutcrops 01 the Cretaceous White Tank monzonite. Note the horizontal pattern of joints inthe outcrop to the left. Photos by author except as noted.

CALIFORNIA GEOLOGY SEPTEMBER 1990 20J

Photo 3. Joshua tree forest at the Monument.

<zo

Blythe IJoshua Tree

National MonumentSan h1ii.

Diego ~lt_----------~

Los Angeles

'-'~'---Q'~')", .~(~=~S-~'~'Palm

Springs

Figure 1. General location map of Joshua Tree National Monument.

The name, Joshua Tree NationalMonument. is derived from the exten­sive stands of conspicuous Joshua treesthat grow within its boundaries. Joshuatrees grow at elevations of 2.000 to6.000 feet and have keenly pointedbayonet-like leaves that bristle at theend of large club-like branches. Untilyoung Joshua trees attain a height ofsix feet. their trunks have leaves thatreach the ground. As the plant agesand grows in height. these first leavesdroop. die. and become closely pressedinto a thatch-like mat that covers thetrunk and limbs. Some trees havereached heights of 54 feet. The Joshuatree is one of four species of yuccasthat are native to California (Vasek andBarbour. 1988). Its unusual and some­times bizarre shapes have made it asymbol of the California high desert(Photo 3).

.....:

Photo 4. View north across Queen Valley to the Pinto Mountains. This valley was causedby extensive weathering of the underlying rock.

Much of the Monument is part of theTransverse Ranges. however its eastern­most portion extends into the MojaveDesert. There are several distinctmountain ranges within the Monument(Figure 2). Valleys between thesemountain ranges were formed by twodifferent processes: (1) some valleyswere formed over geologic lime by ero­sion. and (2) some valleys were formedby down-dropped motion along faultsthat formed basins (called "graben val­leys"). Queen Valley. at 4,400 feet inelevation in the central part of theMonument, is an example of a valley

formed by erosion (Photo 4. Figure 2).Pleasant Valley. located between theUtile San Bernardino and Hexie moun­tains. is an example of a graben valleyformed by faulting. Both valleys arediscussed in the Geology Tour Road log(Figure 2).

GEOLOGY

The known geologic histoty of theMonument spans about 1.5 billion yearsand includes extensive periods of sedi'mentaty deposition. igneous intrusions.

metamorphism. and erosion. The old­est rocks in the Monument. the PintoGneiss (pronounced "nice"'). have beendated at about 1.5 billion years old andcontain deformed sediments. Sincethese early sediments were deposited.this region has undergone several peri­ods of both tectonic uplift and submer­gence beneath the sea. Although thecomplete geologic histoty of this areamay never be fully known. scientistshave been able to decipher a partialchronicle from the rocks that occur inthe Monument (Photo 5).

CALIfORNIA GEOLOGY SEPTEMBER 1990

Photo 5. Outcrop of Pinto Gneiss. the oldest rock in the Monument.Note the 2-inch diameter lens cap in the upper middle ot photo forscale. This photo was taken at Stop 14 on the Geology Tour Road.

Pinto Gneiss

The Pinto Gneiss varies from prominently foliated darkgray to a faintly foliated much lighter gray. The deformedsediments and possible volcanic material included in this rockprovide the earliest geologic record in the Monument. Al­though the absolute age of these sediments is difficult to de­termine. geologists have radiometrically dated the PintoGneiss at between 1.65 billion years old and 1.4 billion yearsold rrrent. 1984). This unit originally covered a very exten­sive area of ancestral southern California. After deposition ofthe sediments. granitic intrusive rocks invaded this unit. meta­morphosed it. and were subsequently incorporated within it toform the gneiss we see today (Rogers. 1961; Wanrow. 1975:Trent. 1984).

Igneous Rocks

At least four separate large igneous intrusions. called"plutons." later invaded the Pinto Gneiss. The oldest intru­sion occurred dUring the Jurassic Period, and the threeyoungest intrusions occurred during the Cretaceous Period.The exact dates of these regionally significant intrusions.

however. is not known. From abundant radiometric dates ofother California plutonic intrusions during this period. it isestimated that these intrusions occurred between 186 millionyears ago (Mid Jurassic) and 125 million years ago (EarlyCretaceous) ITrent. 1984).

Each of these four regionally significant plutonic intrusiveepisodes is distingUished by a specific rock type. From oldestto youngest these rock types include: (l) Twentynine Palmsmonzonite. (2) Queen Mountain monzonite. (3) White Tankmonzonite. and (4) Oasis monzonite. Monzonite is a graniticIight-colored igneous rock that is predominately composed ofpotassium feldspar and plagioclase feldspar minerals. Feldsparminerals are aluminum silicates containing one or two metalsand are the most common rock forming minerals on Earth.Feldspar minerals are nearly five limes more common thanquartz. Plagioclase feldspar minerals contain varying percent­ages of sodium and calcium metals.

The oldest plutonic intrusion in the Monument is repre­sented by the Jurassic Twentynine Palms monzonite and ischaracterized by large crystals of potassium feldspar withlengths of up to two inches rrrent. 1984). The second oldestplutonic intrusion in the Monument is the Cretaceous QueenMountain monzonite.

Outcrops of the younger lighter-colored Cretaceous WhiteTank monzonite are prevalent in the western region of theMonument. Although this unit resembles the Queen Moun·tain monzonite from a distance. it differs from the QueenMountain monzonite in several ways. The White Tank mon­zonite is finer-grained than the Queen Mountain monzonite: itcontains small amounts of biotite and/or muscovite and. un­like the Queen Mountain monzonite. it contains no horn­blende (Trent. 1984).

The most conspicuous rock outcrops that visitors see asthey drive through the Monument are the bold White Tankmonzonite boulders (Photos 1 and 2). These conspicuous out­crops provide an arresting landscape panorama. The roundedand eroded rock outcrops in the western region of the Monu­ment were formed by erosive agents along joint planes (sub­parallel fractures) in the White Tank monzonite. This graniticunit is feldspar-rich and quartz-rich igneous rock that hascharacteristic joint sets that intersect at nearly right angles(Rogers. 1961).

The youngest plutonic intrusive rock in the Monument isthe Cretaceous Oasis monzonite. Unlike the three older plu­tonic rock units. the Oasis monzonite contains a characteristicassemblage of muscovite and blood-red garnet minerals that.although small, can be seen without magnification. The mus­covite grains impart a glittery appearance to the rock onsunny days (Trent. 1984).

[n addition to the regionally significant monzonite plutons.numerous smaller igneous intrusive rocks occur throughoutthe Monument. One of the most extensive of these is theGold Park diorite. Diorite is a dark colored granitic rock that

CALIFORNiA GEOLOGY SEPTEMBER 1990 205

Joint patterns are easily observed inthe White Tank monzonite. Threedominant joint sets produced spectacu­lar rock forms in this unit (Photos 1 and2). One joint set is oriented horizontallyand was caused by the release of pres­sure when the thick layer of originaloverlying rocks was removed by exten­sive erosion [frent. 1984). Another setof joints in the White Tank monzoniteoccurs vertically and roughly parallelsthe contact of this unit with surrounding

Unlike faults. no appreciable move­ment occurs along rock joints. Jointsare fissures in rocks and commonly oc­cur in recognizable patterns (Figure 3) .Within the Monument. joints have oftenformed parallel sets. and joints with twoor more parallel sets. called "joint sys­tems." also occur.

trend east-west and are associated withfault escarpments or "scarps." Thesemajor fault scarps fonn a linear trend atthe base of mountain cliffs and wereproouced by fault movement. Faultmovement occurs as an up-and-dovmmotion. horizontal sliding motion. or acombination of up-and-down and hori­zontal sliding movement. Alluvial fansand pediments. geomorphic featuresformed by an accumulation of looserock material deposited onto broad val­leys or plains. subsequently developedadjacent to these fault scarps.

Mileo

'"Figure 2. Location maps showing some.. geomorphic tealures in the Monument

and the route of the Geology Tour Road.

Joshua Tree National Monument

,,~'"CO,. ~

'0",WOOD MTNS.

PINTO MTNS.

,-----11 To Twentynine Palms

Jumbo Rocks Ell jCampground

Geology Tour Road

Faults and Joints

Faults are fractures in rock where dis­cernable movement has occurred. Themajor faults within the Monument. suchas the Eagle Mountain fault that can beseen along the Geology Tour Road.

>-

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~

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,,'"~ 5~~

~~ lost6o~ Horse

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m Hill 8'"z 9';,

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is rich in plagioclase feldspar and con­tains a small amount of quartz. Basaltoccurs at three places within the Monu­ment: (1) near Pinto Basin where itformed as an extrusive flow, (2) at Mal­apai Hill where it cooled in place anddid not penetrate the surface. and (3) inthe Lost Horse Mountains where itformed a volcanic dome and cooled toform distinctive columnar joints (Figure2; Trent. 1984).

The most recent of all igneous intru­sive rocks in the Monument include nu­merous dikes of various widths and rockcompositions. These dikes are com­mon throughout the Monument andcross-cut all of the previously mentionedrock unlts.

:.-- Hidden Valley IICampground

"" CALIFORNIA GEOLOGY SEPTEMBER 1990

(A) Front view of a cross-section throughthe monzonite after the overlying PintoGneiss had eroded away about 20 millionyears ago. As this overlying unit erodedover geologic time, the release inpressure from the massive weight ofgneiss caused the monzonite to formextensive sets 01 joints.

(B) Following a long period of a muchwetter climate than exists here today, themonzonite underwent an extensiveperiod of decomposition that was causedby downward percolating groundwateralong the joints.

(e) With continued erosion, boulder·mantled outcrops formed during the pastfew million years.

with its accompanying brochure. Geol­ogy And Man (Wanrow, 1975). providea step-by-step guide about geologicprocesses that shaped the desert land­scape we see today. The follOWing Ge­ology Tour Road log explains the for­mation of a fault scarp and a dry lakebed, how granite weathers in the desert.and how sand dunes and alluvial fansform.

(0) The White Tank monzonite today.

Figure 3. Schematic diagram illustratingthe formation 01 White Tank monzoniteoutcrops in the Monument. Adapted fromTrem (1984).

GEOLOGY TOUR ROAD LOG

Although the dirt road is readily ac­cessible by car. you may prefer to ride adirt bike. It takes about two hours tocomplete the tour by car. Park rangersadvise bringing drinking water. Theyalso recommend that you end the tourat Stop 9 when the road becomes wetduring the rainy season.

rock units. The third joint set in theWhite Tank monzonite is also verticalbut is approximately perpendicular tothe other vertical set. This system ofjoint sets results in rectangular-shapedblocks that can be obselVed along theGeology Tour Road.

Monument naturalists designed an18 mile self-gUided motor trail louralong a dirt road that winds through themost interesting geology in the Monu­ment. The Geology Tour Road has 16sign posts where vehicles can pull overand stop (Figure 2). The tour, along

The numbered stops at the beginningof each description correspond to num­bered markers along the tour route.Mileage starts at the intersection of theGeology Tour Road and the black­topped main Monument road. The tourroute is a closed loop that returns youto the starting point.

CumulativeMileage Mileage RQADLOG

0.4 0.4 SlOp 1. WHY A VALLEY? Queen Valley(elevation 4,400 feet) is one of two types ofvalleys along the tour (Photo 4). This and LostHorse Valley to the west were formed by adifferent rate of erosion between the satter rockunderlying the valleys and the more resistantrock of the surrounding mountains. Because therock beneath these valleys is less resistant toerosion than the rock forming the surroundingmountains, it disintegrates sooner and formsthe low-lying plain you see at this stop.

0.8 1.2

The other type of valley. Pleasant Valley. (seenlater on the tour), is the resull of faultmovement that produced uplift to the north andsubsidence to the south.

Stop 2. A RAINBOW DIVIDES. This knoll is thenorth-south drainage divide for the Monument.Water drains from this point either to thenorthwest via Quail Springs Wash. or to thesoutheast via Fried Liver Wash into PintoBasin. The erosive force of running water playsan important part in shaping the desertlandscape.

CALIfORNIA GEOLOGY SEPTEMBER 1990 207

1.7

0.3

2.9

3.2

Stop 3. NATURE'S GUTIER. Here. runoflwaler accumulates 10 !arm a wash. During thesummer months, intense rainstorms oflenproduce !lash floods along many desertwashes. Weathering processes physically andchemically break down rocks into smaller andsmaller pieces. and eventually 'orm soil. Theloosened malenal is carried to lower elevationsby water and deposited. These deposits, calledalluviallans, will be seen later In the lour,

The increased soil mOisture along thesewashes allows certain plants. such as theCalltornia iuniper, to grow more vigorously herethan in the drier surroundmg desert.

Slop 4. OLD EROSIONAL lEVEl. Many 01 thequartz monzonite boulders to the east altharoad bear a distincl groove or band aboutseven leet above ground level. ThiS grooveindicates an old erosional level when the soilsurface remained at a static level for anextended period of time. Weathered sandgrains from the granitic rock Wind·blasted therock and lormed the groove. Subsequenterosion lowered the soil level. This exampleiIIusttates how changes In climate producecorresponding changes in the landscape.

Photo 7. Eastward view across Losl Horse Valley toward theLost Horse MountainS (Figure 2). Ryan Mountain. in the Iehbackground. illustrales how the light White Tank monzonl1e hasIntruded upward into the much older Pinto Gneiss. Note howthe exposed and more resistant monzonite at Ryan Mountain iscapped by the much darker gneiss directly above It.Photo courtesy of rhe Nationat Park Service.

Photo 6. White Tank monzomte rock piles to the west of the TourRoad at Slop 5.

0.5 3.7 Slop 5. ROCK PILES. White Tank monzomteforms the rock Plies on both sides of the road(Photo 6). This rock was once a deeply bunedmolten mass called magma that forced ils wayupward into the overlYing much older PintoGneiss. The magma cooled without reachingthe surface and crystallized to form a solid rockmass-the White Tank monzonite. Erosionover geologic time stnpped away Ihe darkerPinto Gneiss exposing the monzonite outcrops,

The mountains to the west are composedprimarily 01 gneiss. Ryan Mountain (SA61 feel)displays the contact between these twodifferent rock types (Photo 7). Harder. moreresistant areas within the monzonite form lhenumerous rock piles. Many of these have welldefrned }oint systems (Photo 7). while othereroded White Tank monzonile rock masseshave collapsed into jumbled Plies (Photo 6).

0.6 '.3 Stop 6. ROCK SCULPTURE. Aher the WhiteTank monzonl1e solidilied. it was fractured byregional geologic forces into joints. Thesejoints usually occur in two sets and intersecl atnearly righl angles. These }oint planes acted aszones of weakness and. over geologic lime.erosive agents readily attacked the monzoniteatong these joints. The result is bouk:lers whichare roughly rectangular in shape. A massiverectangular boulder to the east of the roadillustrates lhis type of erosion (Photo 8). Manyof these boIJlders weather into grotesqueshapes alld have been given such descriptivenames as the 'Skull" (found near JumboRocks) and Ihe "Trojan" and "The Ox" (foundalong the Hidden Valley Nature Trail).

Photo 8. Massive rectangular monzoniteboulder (in center of photo) just 10 lhe east 01Stop 6 is about 131eet hlQh.

208 CALIFORNIA GEOlOGY SEPTEMBER 1990

Photo 9 Malapa1 Hili :).. mile due west 01 Slop 7. ThIs IllOIIld ISeonposed 01 clark basa~ and formed as a mollen mass ot magmatIat intruded through the SUIlOtXlding White Tank monzonite,IIowever. I' did not reach ltle su1ace Extensive erosion ovelgeologic time has weatnered away tile less resistanl Whlte Tankmonzonte

Photo 11 l~ fI'IOI1ar hole dn \od into theWh.le Tank monzoMe at Stop 9. T_-inc:t1Ions C;lP lor f,cale.

Stop 9. SQUAW TANK ArchaeologlC3llrtyes~gatlons reveal [hat nomadICI~IrIhabiled this aUla from about 1000 A.D. ul"l1lthe earl)' 1900s Squa..... TanI< .....as a lavor~e

campsite because ot the I'\Ilturlll water catchbasin Bow!-li"e mor1ars were hollowod mio tloquartz monzon,te and _,e IJ!Mld 10 gnnd seedsand other bits 01 'ood irto meal Sev.,.al 01these bedrock mortars ea.n be soen juSI f,oufl01 me large rock In front 01 you (PhoIO 11)

A concrete dam just to the SOUheast. andrndden In the wash. forms SQuaw Tank (Phclto12). Ca!tlemen wit !hIS <V1d other smJar damsto calch runcff water lor their callie dunng theearly 19005 M.1Iny 01 these small catchmentda'ns are Iocaled where natural pools 01 watftfcollected alter rams. 11 '''las 1'1 such places thatthe Indians also OOlarned waler and illS logICalto assume thaI they ca<nped al ttis spotDeca!Jse OIIIMl natural catch·basln

"O'

Photo 10. Vl€W west across an alkNallan toward Lost~Mourulrls at Stop 8

Stop 8. ALLU.... IAL FANS You aro nowdescending IltlIl'UVIollan (Photo 10). Noticea Slmtlar Ian oXlending from 1110 mounlans ,nlOtho vaJ;ey 10 the SOIIlh Thfi. fans aftco~ed of sards, graV9k. cobbIft;. andbouldel'5 produclid Irom me erosoon aI rocks at"'OhM elevatIOnS Ths roell malenal ,s earnedby gav'ly and 'Iood watets to IowfK levelsWhen flood waters reach the alluvial tans. !helarger. heaVl8r rocks drOP Irst and the bgh1ergravels and sands are earned farther 0Ul Irtothe valley before they settle Alluvial lOInsi1kJSlrate me constant changes In the desertlandscape. MountaJl'ls are constantly beinge'OdecI by geolo;lC processes as the erodecImalenal is dep)$lted I" the aIVvIaJ lans

From Ins SlOP a 314 mle nalUIe D'al 10 thebase 01 Malapai Hill offers you an oppof\un~y

to Inspect Oil oasaltJc lnrusio'l up close Thenaum ..a. wallllakes about 45 ITNnu'es 10ccmplele, A balanced rock occurs along thenature lraa about 1/" mile weSI

Slop 7. MALAPAI HILL Throo quor'IC1r5 cI amile west of \tus point the tW'n peake ofMalapal HAl "'"iii about '00 leet above thevOlley 11oסi" (Photo 0). The hM ~ composed ojbI;ck basal1 aocl IltSulled from a shallowInJllCbon 01 bilSaltlC nagma wtliCh did not QUitereach !he sorlace ollhe Earth It ~ had reacnedlhe surface. a lava flow or volcano would havereMlfled. bullhere IS no eviderce 01 such afIo...-. The MalaPai Hil basalllnlruded l~ WhrteTMlk monzorote a'ld is therelo'9 vounger,A1lhouoh I1S true age 15 unknown. It appearslikely tha.t It was emplaced Cllnng the last lYIOor ftIfee milton years. In CO'TlpatlSOll ID thePlflto Grle ss. 'Atuch 1$ about 1 5 b1llon yearsold, \t'Ie Malapa' hl1 basa1 IS a geologx;allyrecent rock 1;011.

.,

O'

0'

CAlIFOFIN!A GEOLOGY SEP1EMBER 1m

0.2

"0

5.8

Photo 12. Concrete dam al SlOP 9.Cenler of dam is about 9 feel high.

DIKES. Notice the light-colored ballds of rockcu"ing across many altha monzaMe bouldersin this area. These bands. called dikes. wereformed when molten rock 01 a dlNeren! le~lufe

Intruded Inlo joints In the already-formedmonzonite. Many of these dikes are composedof a light-colored, fine-grained rock calledaplite. It is much harder and more resistanllOerosion than the monzonite, and stands out inrelief when the monZOnite erodes. An excellentdike that forms a wall can be found to the eastof the road a short distance beyond this stop.

STOP HERE IN WET WEATHER ANDRETURN TO THE MAIN BLACK TOP ROAD.

Stop 10. PLEASANT VALLEY. As you roundedlhe bend and viewed the expanse of PleasantValley in front and 10 the right. did you notICelhe steep mountain 'ace 10 your lefl? Thissteep easJ.!o·west trending mOtJntalnescarpmenl is a fault scarp and was 'ormed bymovement along the Eagle Mountain 'ault(Photo 13). A little farther to lhe eastth,s 'aullcombines with lhe much larger Blue CuI taultalso a east-west trending tault. which has a so·mile trace stretching 'rom the western 'oot ofthe lillie San BernardinO Mountains to lheeastern edge of the Pinto Basin. The EagleMounlaln fault scarp IS part ot a fracture zonethat varies from 300 to 1.000 feel in width andfollows the base of the mountain before you(Photo 13). North 01 the fault, lhe Pinto Gneisswas hlted up relative 10 the landscape on thesouth. Geologists call Ihls type 0' 'ault a"normal" 'ault. The combination 01 up-lill anddown-drop created Pleasanl Valley. the secondtype ot valley lhat you have seen (the first wasQueen Valley, a result ot dillerential erosionbetween rock lypes),

CALIfORNIA GEOLOGY

The Blue Cut fault is named for the granodlorlte(a combination ot granile and diOrite minerals)that has a "bluish" linged color possibly causedby Slressed quartz or stressed 'eldspar thatoccurred along lhe fault zone. The Blue Cuttault scarp and its associated blUishgranodiorite IS exposed on the mountainsidedireclly to the west and across Pleasant Valley

Ptloto 13 View toward the southeasl aJong the Eagle Mounlainfault zone thaI runs aJong the base 0' lhe mountains where lheymeet the deser1 lIocr at Stop 10.

PETROGLYPHS, Petroglyphs or Indian rockcarvings can be seen abool 1SO feet to thenorth 01 this stop (PhOlO 14), This ancient artIS 'ound on rocks coaled with thIn "desertvarnish," a dark chemical deposit whICh formson desert rocks over lime. Indians chipped thisvarnish layer away 10 expose lhe much lighterrock beneath. These carvmgs may have hadsome religiOUS meaning 10 lhe Indians, bUl thisis only conjecture. Some petroglyphs m IheMonument may be thOtJsands of years old:desert varnish has reformed on somecarvings-a weathering process lhat lakesconsiderable time. ptease help prOlect thisprehistoric Indian art.

SEPTEMBER 1990

Photo 14. Indian petroglyph carved into desert varnish.

'0 6.8 Stop 11. DRY LAKE. This dry lake, also calleda desert playa. that you are now crossing isevidence that a wetter climate eXisted here. Apenodic lake once lilled Pleasant Valley andlacustrine (lake) sediments were deposited inthis lake to a depth of hundreds olleet. As thelake evaporated, salts cryslallized andprecipitated out of the water. Several similarplaya lake beds In other parts 01 the Californiadesert are mined commercially for a van~lty 01salts, such as borax.

solUllons carrying these dissolved metalsmigrated upward from lhe invading magmathrough the surrounding older rock. As theset1ulds cooled. the melals precipitated out andwere dePOSited along pre-existing Iractures orfissures to form are vems. Quartz is oftenassociated With these veins and is used as anIndicator for possible are deposits.

Pholo 15 Mine shafts al SlOP 12. Abandoned mine shafts andadlts are dangerous and should be avoided: nOle the barbed·wlreposts surrounding the shafl.

0.' 7.2

SAND DUNES. To the left, notICe the sanddeposits and the start 01 sand dune formalion.This is typical at areas where there is a sourceof sand (the playa), and an open tlal area(Pleasanl Valley) where wind picks up sandparticles and cames them to lhe mounlalntrant, which acts as a barner causing the sandand silt to lall at lhe mountain base and formsand dunes.

Stop 12. MINES. The mountain slopes In Irontand to the north are honeycombed wllh tunnelsand shafts dug by miners looking lor gold andother precious metals (PhOlO 15). There wasextenSive mining activity throoghout lhls areaduring the lale 1800s and early 1900s. Veryfew of the mines. however, proved lucralJYe:the Lost Horse mine in the Lost HorseMountains (Figure 2) is one excepllon. Gold,silver. copper, lead. and other metals ateconomiC importance were deposited when theinlfudmg White Tank monzonite magma cooledand crystallized. Various gasses and lIQuid

'9

0.8

9.1

9.9

Stop 13. CATTLE RANCHING. Here. along thebase at the alluvial lan, lhe soils are deeperand more runoff water accumulates. The addedmoisture allows for more vigorous plant growthsuch as grasses. In the lale 1870s, ranchersmlroduced Texas longhorns to this areabecause of the lush vegetation. Over.grazmgand a long droughl after 1932 led to the declineof catlle ranching. The numerous cholla cacti inlhlS area indicate thiS rangeland was over­grazed. Grasses died from lack of nutrients andwere replaced by cactus. With theestablishment of the Monument in 1936. canlegrazing was eliminaled, allowing the range topartially restore itself.

Slop 14. PINTO GNEISS. The banded andfolded rock to your lell. the oldest type of rockin the Monument, IS PInIO Gneiss. Allhough ilSabsolute age is not known, it is thoughlto beaboul 1.5 billion years old (Photo 5). Whereasthe basalt at Malapai Hill and the quartzmonzonite are Igneous rocks-the product at a

CALIFORNIA GEOLOGY SEPTEMSEA 1990 211

coaled magma-gnelss is the product ofmetamorphism. Metamorphism with its Intensepressure and/or heat causes physical changesto occur in rock. The Pinto Gneiss wasonglnally sediments that were laid down Inancient lakes Of seas, and have undergoneextenSive alteration due to the pressure 01overlying material and heat caused by invadingmagmas. This change resulted In therealignment 01 the chemical constlluentS of the'ormer rock to produce a completely dllferentrock.

0.0 9.9

LICHENS. The bright splotches of color foundon many 0' the rocks are primitIve forms ofplant lile called lichens. The different colorsindicate different species. Some form a weakcarbomc acid that chemically breaks down rockto form soil. These tiny plants form a veryimportant part of the erosional cycle.

Stop 15. PINYON WELL JUNCTION. The dIrtroad to the lell leading into the canyon is adead end road and not part 01 the GeologyTour Road. A well in this canyon prOVidedwater that was used 'or processing 01 gold oreand lor canle. The well is now dry.

0.1 10.0 Stop 16. PANORAMIC VIEW. Aside from beingan outstanding picture point. this stop alfordsyou the opportunity to review at one glancemany of the geologic processes seen along thetour (Photo 16). Geology is the study of thehistory of the Earth and is manifested byconstant changes in the landscape. Thesechanges Involve the building 0' mountams. theirdestruction, and subsequent rebuilding. We seeevidence of mountain building in the mountainrange formed along the Blue Cut fault north ofPleasant Valley. We see mountains formed bythe igneous intrusions at Matapai Hill and theWhile Tank monzonite. And linatly. we seegeologic processes eroding these mountainsand depositing the eroded materiat onto thedesert lloar to produce playas, allUVial fans.and sand dunes.

To return, contmue 2.2 miles to Squaw Tankand Irom there 5.5 miles to the main Monumentroad in Queen Valley. As you approach theSquaw Tank area. notice the mountains to theeast which have an excellent contact 01 darKPinto Gneiss in contrast With the adjacent muchlighter White Tank monzonite.

REFERENCES

Rogers, John J.W.. 1961, Igneous andmetamorphic rocks of the western por­tion of Joshua Tree National Monument:California Division 01 Mines and GeologySpecial Report 68, 26 p.

Trenl. 0.0" 1984, Geology 01 the JoshuaTree National Monument: CALIFORNIAGEOLOGY, v. 37, no. 4. p. 75-86, April.

Vasek. F.C. and Barbour. M.G., 1988,MOjave desert scrub vegetation in Bar­bour, M.G., and Major. J.. editors. Ter­restrial vegetallon 01 Cahlornia: Cali/or­ma Native Plant Society, p. 857-858.

Wanrow, Elden K., 1975. Geology andman: an 18-mile sell-gulding motor na­ture trail: Joshua Tree Natural HistoryAssociation. 8 p. ~

Photo 16. View to the north across Pleasant Valley Irom Stop 16. Malapal Hill is to lhe lef\,the Hexie MountainS and the Eagle Mountain fault zone at its base are to the right. TheWhite Tank monzonite is in the distance and the Geology Road can lust be seen as a lightwavy band in the middle.

CALIFORNIA GEOLOGY SEPTEMBER 1990

A Page for Teachers

Mineral Crossword PuzzleMinerals are the building blocks of lhe Earth's crust and in combinations make up the rocks. Minerals

have the following characteristics: (I) they are naturally occurring and inorganic; (2) they have chemical com­positions and physical properties that are fixed or vary only slightly; and (3) they have a characteristic inter­nal structure (called crystal lattice) determined by a fixed, orderly arrangement of atoms. Different mineralshave different properties (such as color. Iusler. hardness. streak. cleavage. specific gravity, and crystal form)by which they can be identified. For basic information on minerals see Division of Mines and Geology Spe­cial Publication 33. MMinerals and Rocks~ ($1.00), available from DMG. P. O. Box 2980. Sacramento. CA95812-2980.

The crossword puzzle can be used as a special interest activity alter the study of minerals. It is suitable forgrades 6 through 12. ..Puzzle courtesy of Carol Stadum. Department of Geological Sciences. CaliforniaSlate University, Fullerton. California.

ACROSS CLUES

transparent fleXible minerai with goodcleavage

2. brown aluminum are3. naturally occurflng inorganic mixture4. minerai used to make plaster5. a hole in a rock7. German mineralogIst made this

hardness scale8. soapstone

11. specific gravity15. a mlTleral family with Silica and oxygen16. minerai form determIned by atom

arrangement17. quartz;s this hardness20. number seven on the hardness scale22. the minerai form of nJst23. rock salt

DOWN CLUES

1. a metallIC liqUid native mineral4 a round cavity lined with crystals6. minerai used to make pendllead9. a crystal tamlly that has all sides equal

and at right angles10. naturally occurring inorganic compound

or element11. hardest known mineral12. rough broken minerai surface13. thiS mineral fizzes In acid14. the metallic or nonmetallic shine of a

minerai18. fool's gold19. powdered mineral color21. oHidal California State Minerai

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See page 214 for answers 10 Mineral Crossword Puzzle. OX'

CALIFORNIA GEOLOGY SEPTEMBER 1990

John WolfeRetires

John Edward Wolfe. Executive Officer of the State Boardof Registration for Geologists and Geophysicists. \Nil! retire inOctober, 1990. John has been in state service since 1956and has been an Exe<:ulive Officer with the Board since1969. The Board is responsible lor licensing and overseeingthe professionalism of geologists. geophysicists. and engineer­ing geologists in California. Applicants interested in the posi­tion left vacant by John's retirement can request informationfrom the Board office at: Geology and Geophysics Board.10210 Street Room A-190. Sacramento. CA 95814, ~

(From poge 213 .. .)

Alfred O. WoodfordMemorial

Dr Alfred O. Woodford. long-time California geologist andfounder of the Pomona College Geology Department died onJune 29. 1990. He was 100 years old. Professor Woodford.called "Woody· by his friends. did much to advance the sci­ence of geology in California (see the May_ 1989 issue ofCAUFORNIA GEOLOGY). He wrote many articles and sev­eral popular textbooks about geology. In recognition for hiswork. Woodford received the Neil A. Miner Award. the high­est honor bestowed by the National Association of GeologyTeachers. During his career he was president of the Cordille­ran Section of the Geological Society of America. and presi­dent of the National Association of Geology Teachers. ~

M Ilc AI~AUXITE

ROICKIC

Answers toMineral

CrosswordPuzzle

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2" CALIFORNIA GEOLOGY SEPTEMBER 1m

NWWAGroundwater Seminars

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520.00

5 9.00

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Proc. includ.spostoge ond loles to>

For further information contact,NWWA Education Department for pro­gram information or the RegistrationDepartment for registration informationat 6375 Riverside Drive. Dublin. OH43017.(614)761-1711. 'X'

This one day course will address:laws and regulations prompting environ­mental site assessments. scope of envi­ronmental site assessments. the preac­quisition environmental investigationreport. responses 10 environmentalproblems and minimizing the liability ofthe consultant.

Ind.cote numb.r 01 copies

TOTAL AMOUNT ENCLOSED

SPECIAL PU8l1CATIONS__ SP41 80sIC placer mInIng. 1946__ 5P92 CAllFOI1NIA GEOLOGY mogOllne Inde~ 1948-1986.

•SPECIAL I1EPOI1T5__ SR143 POrl 5, Mln.rolland cloulfic:otlon of the greoler Los Angeles oreo, c1ossificotion

of send on.d grovel resources oreos, Sougus-Newholl production·consumptionregIon ond Polmdole productIon-consumptIon region.1987 (newl . . . • . . . . . . . . . . • . . . . . . .••..•.. 5 8.00

__ 511146 Port I, Mlnetolland clOSSlflCOtion: oggregote moteriols in the Son ftonc;sco­Monlerey Boy oreo - projecl descriplion (1986)

__ 511146 Porl 2, Mlnerollond c1onificotlon: oggregole moteriols In the Soulh SonFrancisco 80y oreo. 1987 .

__ SI1146 Porl 3, Mlnerollond c101S,ficotlon: ogg,egole malerio/s in the No"'"Son fronclsco·Monlerey 80y oreo. 1986

__ 511146 Pori 4, Mlnerollond clon,ficotlon: oggregOle male"ols In the Mont".y Boyregion, 1990. (new) 520.00

__ SR1S6 Mlnerollond dOUlfICOl!On of porllond cemenl concrele·grode oggregote,n the Socromenlo-Folt!ield ptoduchon-consumplion region. 1987. (new) . • . .. 518.00

__ 51116J Surfoce ond g'Ol.Indwolet monogemenl in surface mlned·lond reclomOtlon.1989 (newl ....

CALIFORNIA GEOLOGY__ 1yeo' (12 ,nues) . . _...••.•....•.••.....•.__ 2 yeors (24 issues) .•.. . .__ 80ck issues Ispecify volum. ond monlh). IndiVIdual issues 51.25 lOch__ L,st of Avoiloble Publicotlon. .

November 9. 1990Bally's Las VegasLas Vegas. Nevada

This seminar will emphasize monitor­ing. sampling and remediation in thevadose zone. Sessions will concentrateon: soil pore-liquid monitoring. monitor­ing for underground storage tanks. va­dose zone monitoring concepts forlandfills and surface impoundments.soil-gas monitoring. remediation usingIandfarming techniques and real estatetransfer sites.

I1 PAYMENT MUST SE INCLUDED WITH OI1DfRL _

• Environmental Site Assessmenl$One-Day Course.

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October 23-25. 1990Sheraton Palace HotelSan Francisco. California

• A Comprehensive Approach toDevelopment and Protection ofGroundwoter Supplies

Sessions will focus on: sources ofgroundwater supply. maximum supplythat can be developed. groundwaterlaw. sources of contamination. chemi­cal and physical characteristics of con­taminants. groundwater vulnerability.groundwater protection regulations.and groundwater data and researchneeds.

October 1-3. 1990Ramada Renaissance HolelLong Beach. California

• Theory and Application of VadoseMonitoring. Sampling and Remedia­tion

• Theory and Practice of Groundwa­ler Monitoring and Sampling-De­signed for Newly Practicing Ground­waler Professionals

The Association of GroundwaterScientists and Engineers. a division ofNational Water Well Association(NWWA). will offer the followingseminars.

November 6-8. 1990Bally's Las VegasLas Vegas. Nevada

This seminar examines the monitor­ing process and procedures for ob­taining representative waler samples.Instruction is given on, groundwatermonitoring system design. advantagesand limitations of various drilling meth­ods. soil sampling methods. field testslor defining aquifer parameters. mate­rials used in monitoring well installa­tion. well development. selecting sam­pling devices. sample frequency. mini­mizing outside influences on sampleintegrity. and vadose zone monitoring.

CALIFORNIA GEOLOGY SEPTEMBER 1990 '"

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D£f'AlTMENT Of CONSaVAT1QNCAUFORNIA GEOlOGY

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California Journal of Mines and Geology- Back Issues Available -

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PAYMENT MUST 8£ INCLUDED WITH ORDER INAME -==========-

A limited number of California Jour­nal of Mines and Geology separates areavailable for purchase. The issues datefrom 1934 to 1958 and have longbeen 001 of print. Mosl separates wereoriginally published as chapleTS of theAnnual Report of the State Mineralo­gist These chapler separates includein-depth desoiphons of individual Cali­fornia mines. mineral resources. andgeclogic processes.

Available issues, current prices. andtheir feature articles include:

January 1934, (State MineraloglSl's ReportXXX). v 30. no 1 $5.00 each(90 copieS available)."AesurrecllOO 01 early surfaces In thes.erra Nevada:"Geology and lfUneral resources of north·easlern Madera County.-'Geology and rrHneral deposits 01 laureland CorMC1 baSIns, southwestern MonoCounty."

October 1944, (SIale MlflflfaloglSl"s ReportXl), v. 40, no 4 $5.00 each (49 copteS

available)."Pellet phospho(lte 'rom Carmel Valley.Monterey Count)'."

"Geology 0' the Ouartz Crystal mine nearMokelumne Hill. Calaveras County ""StrategIC mICa:~Markellng vermICulite.-

April 1945, (Slate MlflflfaJogtst s Report XLII,v. 41, no 2 5500 each (170 copesavarlable)"Quicksilver deposits ollhe KnollVllIe DIs·tncI, Napa. Yolo and lake countJeS-

October 1945, (Stale Mlfl8faJoglSI'S ReportXU). v 41, no 4. $5.00 each (30 cop.esavailable)."Pine Creek and Adamson tungstenmines, Inyo Count)' -"Indelt to topographic quadrangles 01California.""Flow-sheet 0' American Potash andChemical Corporation at Searles lake."

July-October 1957, v 53, no. 3-4 $5.00each (159 copies available).-lead and Zinc In Califorrna -

AODRESS ICITy :

STATE ZIP 1

TOTAL AMOUNT ENCLOSEO .S _

Jan-December 1957, v. 53. $10.00 each(8 ropeS ot the complete bound volumeare av3llable)."Geology of the Island MountaIn Coppermine, Tnmiy Count)':"Mtnes and ITIlTlefal depoSits 01 ManposaCounty -"lead and Zinc in Califorrua:

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'" CALIFORNIA GEOlOGY SEPTEMBER i990