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GEOLOGYA PUBllCATlON OF THE

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In This Issue ITRAVERTINE HOT SPRINGS 171SIMPLIFIED GEOLOGIC MAP OF CALIFORNIA " ,.." 180ELISE MATIISON JOINS CALIFORNIA GEOLOGY STAFF ,.182MARIPOSITE-THE ROCK THAT MADE CALIFORNIA FAMOUS 183DMG BAY AREA REGIONAL OFFICE RETURNS TO SAN FRANCISCO .. 187MAIL OADER FOAM....... . 189GSA HOLDS ANNUAL MEETING IN OCTOBER 1991 190CALIFORNIA GEOLOGY SUBSCAIPTION FORM ... 190CALL FOR PHOTOS RESPONSE: 191

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CALIFORNIA GEOLOGY

Cover Photo: NOI1h Dome (left), Basket Dome (right) and Mt Hoffman (left centerhorizon) from Glacier Point, Yosemite National Pari<, California. These massivegranitic domes have been shaped by exfoUstion (see page 192). MI. HoHman(10,850 leet) is named for Charles Fredrick Hoffman, a topographer and memberof the Whitney Survey, Call1ornia's first geological survey. lis summit owes itsdistinctive jagged appearance to Quaternary glaciers that gouged its flanks. leavinga ridge 01 pinnacles. Kodachrome-54. lOSmm lens, 1125, 1111. Phato by James W.Carlblom, submitted in response to CALIFORNIA GEOLOGY's Call For Photos.

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Utah Geographic Infonnation CouncilFirst Annual Conference-October 30. 1991

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August 1991Nolume 44/Number 8

Southwest ARC/INFO~User GroupFourth Annual Conference-October 31 - November I, 1991

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HO CALIFORNIA GEOLOGY AUGUST 1991

Mono County, CalifomiaBy

CHARLES W. CHESTERMAN and FRANK J. KLEINHAMPL

This article is an abridgment of SpecialRepon 172, Travertine Hot Springs atBridgeport, Mono County, Calilornia, inpreparation at the California Division ofMines and Geology.

The Travertine Hot Springs area is on thenorthern edge of what many consider to beone of the most teetonk:a.lly active areas inthe United States. There is abundantgeothermal and seismic actiVity. Thelandscape is doned with volcanic features­cones, craters, domes, flows, lumaroles andhot springs-lndicators of unrest in thepl'esent as well as reminders of activity inthe past.

Travertine, also known as calcareoussinter. IS limestone 'ormed by chemicalprecipitation of calcium carbonate (CaCOJ )

lrom ground or surface waters. It formsstalactites and stalagmites in caves, fillssome veins and spring conduits and canalso be lound at the mouths of spril'lgS,especially hot spril'lgs. The less compactvariety is called tula and the dense, bandedvariety is known as Mexican onyx, or onyxmarble. True onyx, however, is a bandedsilicate.

The term travertine is derived fromtiverrino, an Italian word for 1rom TIbur:TIbur is the old Roman name for TIVoli. Italy.a city east 0' Rome. There. travertine formsthe falls of the Aniene Aiver. The deposit islamous because it is 500 leet thiCk in placesand because it has provided much of thebuilding stone for Aome since ancienttimes.... editor.

INTRODUCTION

N

I

'---.I BRIDGEPORTIllI\Travertine

Hot Springs Bodie'-"

16

'-.

Figure 1. Location map ot the Travertine Hot Springs area, Mono County, California.

T ravertine Hot Springs. once pri­vately controlled, is now under the

jurisdiction of the U.S. Bureau of LandManagement. It consists of numeroushot and colcl springs that are unevenlydistributed over about 9 acres near thesoutheastern perimeter of the town ofBridgeport. Mono County. California(F"lgure l). The travertine locality is mosteasily reached by turning east off U.S.Highway 395 about 0.6 mile south ofthe junction with Nevada Highway 23onto the paved road leading to the Cali­fornia Department of Transportationyard. The paved road veers to the southand an unpaved road continues east.

1lle unpaved road splits into two, withthe lou.rer. right-hand branch leading tothe travertine area.

The travertine terrace deposits form acompact tabular mass marked with trav­ertine ridges ranging up to 850 feet longand 15 feet high. Hot waters ascendingalong fault-controlled fractures in Ter­tiary volcanic rocks are enriched in cal­cium bicarbonate. When these watersreach reduced pressures at the surface,calcium carbonate precipitates to form

travertine. Porous lightweight travertinecomprises the bulk of the terraces.ridges. and other hot spring features.A dense banded travertine occurs infissures In the ridges.

In the 1890s about 60 tons of traver­tine VJere quarried and shipped to SanFrancisco where polished slabs wereused as ornamental facing stone in therotunda of City Hall. Subsequent quarry­ing has been sporadic and is presentlyinactive.

CALIFORNIA GEOLOGY AUGUST 1991

Pyroclastic depositsof Willow SpringsFormation

Underlain byhydrothermallyaltered rocks

Dacite 0' WillowSprings Formation

EXPLANATION

Fault (dashed whereapproximately located;dotted where concealed;U, upthrown side:D, downthrown side)

"jStrike and dip of beds

",Strike and dipof flow banding

Contact,approximately located

SYMBOLS

... ---_ ......

~ Alluvium

ITufa I Hot spl'ing deposits

~ Terrace deposits

~ lacustrine deposits

-....-...--'T\9tTWd~7655

~,,-.2"~

o

32

5

0"

o"­WOal

" 17o

>­W

-'-'«>

T. 5 N

~0: I

T • , Itf\'al"--------::;:;I.L-'::::::,="~~c==_i~1~~T~~--""~t »'>"'-11.'I

Figure 2. Geologic map of Travertine HOI Springs and vicinity. Modified from Map Sheet 21.Geology of the Bodie 15' Quadrangle, Mono County. California (northwest corner).

GENERAL GEOLOGIC SETIING

Travertine Hot Springs is within thecomplexly faulted western part of theBodie Hills, a volcanic upland thatformed in Tertiary time. Exposed lavaflows and tuff breccia of the Bodie Hillsare chiefly late Miocene in age. To thewest they are overlain by Pleistoceneglacial till and outwash.

circular topographic depression partlybounded by silicic plugs that intrude thering-faulted margin of Ihe collapse zone.An east-striking fault zone extends fromthe caldera west to U.S. Highway 395passing close to the site of The HotSprings. which is located about 1.25miles south of Travertine Hot Springs(Rgure 2, see also Chesterman andGray. 1975).

Springs appears to be a depositional laponto late Miocene dacilic flows. $Orne ofwhich are weakly hydrothermally al­tered. In several places. especially alongthe main drainages. a thin skin of cal­cium carbonate is being deposited onlightly alluviated gully bottoms. Moucdsof calcitic mud also are being depositedon and around grassy vegetation grow­ing on the travertine terraces.

The nearest known volcanic collapsefealure is the 1.5-mile-diameter calderaat Big Alkali. about 4 miles east-south­east of Travertine Hot Springs. Warmsprings at Big Alkali are centered in a

The travertine deposits are assumedto have begun forming in the Pleisto­cene. but have never been preciselydated. The poorly exposed bedrock­travertine contact at Travertine Hot

GEOMORPHIC FEATURES

Featureless travertine terraces areinterrupted by a remarkable series offinger-like fissure ridges. mounds ofvarious sizes. pools, and springs.

CALIFORNIA GEOLOGY AUGUST 1991

Fl\}Ure 3. Map of map~ featuresof the Travertlne Hot Springs area.

300,

N

t

200,'00,FEET

o50

NORTHRIDGE.,

'00,\

Road

,,- ",""'ltlll"UlIIl'"''''''''"',,,,,,,,",,,,

LONG RIDGE'::lil.

~

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)'Spnng

EXPLANATION

Jupiter

~-',-, ' ........

".

Fissure ridge

PhoIo 1. Southwest end of~ Tub RidgeThe phOtO was taken from Itle top of LongRidge. Photo by Efse Maroson.

'~............"--"'''' ""

" ,

_-:::::::: ...- "~\

\

CALIFORNIA GEOlOGY AUGUST 199' '"

Photo 2. View southeast toward segment three 01 Hot Tub Ridge showing step-down relations 01 growth units 1. 2, 3. and 4 from felt toright. Both ends 01 the segment can be seen wilh partial disintegration occurring the length 01 the segment. Middle portion of long Ridgecan be seen just behind distal end 01 Hot Tub Ridge. White material on grass and soit is sodium bicarbonate efflorescence. Photos byauthor, excepf as noted.

Terraces

A series of coalesced travertine ter­races forms an extensive planar apron­like feature upon which smaller traver­tine landforms. chiefly fissure ridges. aresuperimposed or embedded. The ter­races appear to have formed as succes­sively younger fringe-like terraces coa­lesced and extended outward from acore area. An individual terrace fringe.up to 45 feet thick and 295 feet wide.extends 500 feet along the perimeterof the older core terrace. The travertinefringe commonly exhibits a scallopededge along its outer margin. Travertinedeposited around clusters of springscoalesces. forming the scalloped perim­eter of the terrace. This indicates thatsome springs are perennial. Other inter­millent springs and seeps away from thefringing terrace mounds have depositedtravertine. filling surface irregularitiesand eventually producing a relativelyplanar terrace surface. These coalescedmounds are similar in form to theterracettes of Mammoth Springs inYellowstone National Park described byBargar (1978. p. 18) but probably devel­oped differently.

Fissure Ridges

Ridges that rise above the terraces aretermed fissure ridges by Bargar (1978)for similar features at Mammoth

Springs. Most ridges trend northeast toeast (Figure 3), The smallest ridge.named Beta. is about 35 feet long andabout 3 feet high. The longest. LongRidge. has an overall length of approxi'mately 850 feet and reaches 15 feet inheight. Ridge widths range from 10 to80 feet. Features of the ridges includethe body. segments. growth units. andlongitudinal or medial fissure. Thesefissures. which range in width from afew inches to several feet. often separatethe ridges into two halves parallel to themedial fissure. The porous travertinethat comprises the bulk of the ridgeoccurs in crusts that arc around eachend of the ridge to form what is referredto as a carapace (Photo 1).

A ridge is generally parallel to theoriginal fracture along which it devel·oped. Most of the ridge crests slopegently downward. generally in a south­westerly dire<:tion. The ridges are com­posed of layered porous travertine withcoatings of dense vertically-bandedtravertine along the medial fissures'walls.

Ridges are often segmented. Gapsbetween segments represent places ofnon-deposition of travertine rather thanplaces where ridges have been erodedand removed. Several of the ridgesexhibit one or two such gaps.

Field evidence indicates that the bulkof each ridge developed in growth units(Photo 2). Growth units range in lengthfrom several tens of feet to several hun­dred feet. Multiple growth units canoccur in a single ridge segment. Geo­thermal water of varying temperatureascends the fissure and slowly overflowsthe two sides of the growth unit 10 de­posit travertine in irregular and overlap-­ping crusts. The medial fissure extendsthe full length of the growth unit beingformed. The medial fissures are quitenarrow. initially. allowing just sufficientspace along which geothermal water canascend to effect ridge growth. At sometime early in the formation of a fissureridge, its two halves commonly split byslight outward tilling enlarging the me­dial fissure separation to as much as 4feet. The depth to which an openingmay extend is not known. The fissure inNorth Ridge was found to extend slightlybelow the ground surface upon whichthe ridge rests.

The seemingly smooth surface of theend of a growth unit is often cut by asingle vertical mediallissure which ex­tends from the ground upward to thecrest of the ridge. Some fissure ridges.especially North Ridge, exhibit multiplevertical fissures that are nearly equallyspaced. fanning outward across the dis­tal end from the single main fissure.

'" CALIFORNIA GEOLOGY AUGUST 1991

Photo 3. Grass and other lorms of vegetation growing on a mound of calcareous mush. Thismound is in the process of developing around two small circular vents on terrace travertine,Scale is indicated by the 12-inch pick handle.

Fissure Mounds

Elongated mounds that rise only afew feet above the terrace are calledfissure mounds. They are believed torepresent fissure ridges that. for someunknown reason. failed to attain theshape, form, and size reached by thespectacular fissure ridges. Two of thelarger mounds, each about 290 feetlong and together about 30 leet wide,run between and parallel to Hot Tuband Long ridges.

Mounds

A few dozen small mounds composedof tussocks of grass growing in travertinemud are widely scattered across thetravertine terrace (Photo 3). The moundsare rarely more than 3 feet in height ordiameter. Some of the mounds' summitshave one or more pools. All of themounds are believed to be composed oftravertine mud, possibly mixed with algaldebris deposited from hot or coldsprings. The lack of a visible pool atop amound suggests that material depositedaround a minor spring has sealed anorifice. thus forming a ~fossir mound.

Pools

Some orifices are sub-circular holes inthe terrace surface. Water may stand inthe hole or flow out through a minorchannel cut into the rim of the hole.

Some holes are filled with mud and veg­etable debris and are comparable to"fossil" mounds, where orifices havebeen plugged, The largest water filledhole. referred to as Jupiter, is about6 feet across (Figure 3). This pool wasprobably enlarged by man as evidencedby large timbers found in the pool. Thelargest natural pool. referred to as Pluto,is several feet across. Pools are com­monly only a few feet deep, whereas

some exceed 5 feet. Pool bottoms areusually muddy and covered by algaldebris.

Springs

Water from springs and seeps foundassociated with the travertine depositsranges from air temperature to about140QF (60QC). The greatest flow. notespecially impressive as hot springsgo. is about 15 gallons per minute.

CALIFORNIA GEOLOGY AUGUST 1991 '75

Photo 4. Layering in porous travertine on south side ot segment three of Hot Tub Ridge.General strike of steeply dipping layers of porous travertine is almost perpendicular to thelength of the ridge. SCale is indicated by the 12-iflCh pick handle.

DEPOSITION OF TRAVERTINE

Travertine deposition at hot springsoccurs when carbon dioxide is releasedfrom ascending bicarbonate spring wateras it reaches reduced pressures at thesurface. The loss of carbon dioxide,coupled with high evaporation rates.increases the saturation level, resulting inthe precipitation of calcium carbonate.

Two types of tr<lvertine, porous anddense banded, are common at Traver­tine Hot Springs. Allen and Day (1935.p. 377) suggested th<lt porous travertineforms rapidly in crusty layers at a greaterrate than does the dense travertine.They also suggested that some densetravertine may have formed either byslow deposition or by precipitation ofcalcite into open spaces of the poroustravertine. The porous travertine exhibitsslight to major variations in texture orcolor yielding a subtly banded appear­ance in comparison to the obvious band­ing of the dense type of travertine.

Water. channeled away from the springsin some places, may disappear into theterrace to mix with other water beforereappearing in other springs and/or itmay evaporate beyond the travertinecomplex. In other places a sheet-likeeffluent produces a runoff that generallydeposits a crystalline calcite mush acrossthe terrace and even beyond in the gul­lies cut into Tertiary volcanic rocks thatsurround the hot springs area.

There is a tendency for an alignmentof warm and hot springs parallel to thetrends of the fissure ridges, and cold,warm. and hot springs are juxtaposed insome places. The temperatures fluctuateover a few months' time. This variabilityin temperature reflects complex mixingof geothermal water and groundwater ina largely unknown plumbing system.

Most springs. regardless of their tem­perature, are ephemeral. The variation inwater supply may be due either to differ­ences in recharge volumes or to changesin the plumbing system. Conduits maypartly or wholly clog either because ofcementation by precipitating calciumcarbonate or by some minor adjustmentcaused by ground movements.

Photo 5. Rill structure caused by micro·terraces developed in porous ridge travertine. asexposed on the north side of Hot Tub Ridge. SCale is indicated by the pencil.

CALIFORNIA GEOlOGY AUGUST 1991

The porous travertine displays a palebuff color (Photo 4) whereas the densebanded travertine forms layers thatrange from pale gray and cream throughhues of brown and yellow to orange-red.

The porous travertine is. in places.composed of small parallel terrace-likeand step-like structures. or rill structures.These rill structures might be consideredmicro-terraces where a single micro­terrace seldom exceeds a few inches inlength and 1/8 inch in width. Whenfound fully formed they are covered bythin (1/16 to 1/4 inch), fairly continu­ous layers of minutely porous travertinethat yield a sandwich-like structure re­sembling corrugated cardboard (Photo5). The irregularities in the travertinesurface control the distribution. size. andshape of the micro-terraces developingon them.

Photo 6. View eastward to fissure-filling traver1ine in small quarry near eastern end of longRidge. The medialtissure ot the ridge here is completely filled with dense. vertically layeredtravertine. which at this location is about 5 feet thick. Scale is indicated by the 12-inch pickhandle.

The dense travertine generally occu·pies a part or the whole of the verticalmedial fissures of the mounds and ridges(Photo 6). Discrete color bands whichare parallel to the fissure walls range inwidth from less than 1/16 inch to asmuch as 4 inches. They commonly ex­hibit textural variations which are gener­ally functions of the degree of crystallin­ity of the calcite and the amount of im­purities. generally hydrated iron oxides.present in the travertine. Coarsely crys­talline calcite, with grains as much as1/8 inch across. produces white to palebufl-colored layers up to 2 inches wide.Much of the dense banded travertine,however, consists of randomly-orientedcalcite grains smaller than 1/8 inchacross. Scattered uniformly among thecalcite grains are clusters of minute redand brown hydrated iron oxide grainswhich impart the various reddish andbrownish colors to the dense travertine.

A third type of travertine, "calcite ice"(Bargar. 1978, p. 28). is found on thesurface of several hot pools. [t is a deli­cate. thin. whitish crust of calcite whichbreaks up easily and settles to the bot­tom of the pools on which it develops.

HOT TUB RIDGE

Hot Tub Ridge was studied in detail todetermine how a typical travertine fis­sure ridge develops, because it containsan active flowing stream of hot goother-

mal water. The three segments thatcompose the ridge have westward-de­scending steps as shown in Photo 2.The overall profile of the ridge slopesgently from a height of 15 feet to aheight of 10 feet near the terminus tothe southwest. This ridge is about 540feet long including the 15- to 20-footgaps between segments. Segments arenumbered one, two, and three fromnortheast to southwest and are approxi­mately 50. 175 and 275 feet long. re­spectively. Base widths average 15 to 20feel.

Each segment includes a medial fis­sure, a narrow inner terrace. and acarapaced end. There is every indicationthat the three segments of Hot TubRidge developed along the same bedrockfracture from a southwestward-migratingspring-like source of geothermal water.Segments one and two do not containany visible springs and appear to havebeen inactive for a long time. They prob­ably developed earlier, with segment onebeing the first to develop. These older.shorter segments do not now exhibit thewide opening of the medial fissure that isso well-developed in the third segment.

The active segment of Hot Tub Ridge,segment three. is divided into four parts.or growth units. numbered one throughfour from northeast to southwest.Growth unillengths are 50 feet. 135feel. 35 feet, and 55 feet, respectively.A medial fissure extends throughout thecombined lengths of growth units one.two. and three. It attains a maximumwidth of about 30 inches in growth unittwo and thins to less than I inch at thesouthwest end of growth unit three. Thepresence of a fissure in growth unit fouris indicated only by a narrow ditch-likefeature that conducts hot water to thedistal end of the ridge (Photo 1).

The medial fissure is mostly filled withfragmental porous travertine upon whichrests vertically-layered dense travertine 01variable thickness. This sequence of fis­sure-filling travertine is capped by hori­zontally-layered dense travertine up toseveral inches thick. which is referred tohere as inner terrace travertine. There isan 8- to lO-inch-wide inner fissure withinthe medial lissure in growth units oneand two (Photo 7). Near the midpoint ofgrowth unit two, the sound 01 bubblingwater can be distinctly heard in the

CALIfORNIA GEOlOGY AUGUST 199\

rubble-filled inner fissure. The water emerges near the south­western end of growth unit two and flows southwestwardalong the floor of the inner terrace,

Apparently several mecha­nisms. working either togetheror separately, effected development of the medial fissure inHot Tub Ridge. Bargar (1978. p. 23-25) has suggested thatfissure widening in travertine ridges at Yellowstone NationalPark could have been accomplished through pressure causedby crystallization of calcium carbonate. Crystallization fromsupersaturated solutions was a primary mechanism in theformation of the vertically-banded dense travertine in thefissure in Hot Tub Ridge. However. the writers believe thatanother mechanism involving subsidence may have occurred

along the length of the ridge and that this played an importantrole in enlarging the width of the fissure.

Subsequent to the comple­tion of growth unit three. afissure opened along theentire length of the ridge,affecting at least growth unitsone through three. Preciselywhat caused this later fissur­ing is not known. but it isassumed to have been a re­sult of unequal subsidence ofthe two ridge halves. Thisinner fissure was later filledby dense layered travertineextending the full length ofgrowth units one throughthree. The inner fissure is10 inches wide at its widestpart near the crest of theridge and separation de­creases at depth. It is notknown whether the innerfissure occurs in growth unitfour because porous traver­tine covers the projectedextension of the fissure.

An explanation of thesubsidence phenomena maylie in the nature of the mate­rial upon which the ridgesrest. rather than in the ridgesthemselves. The two halvesof a ridge are normally aboutequal in mass and identical incomposition and physicalcharacteristics. The first cal­cium bicarbonate waters toascend along the fracture in

the bedrock and soil would precipitate calcium carbonate atand near the ground surface and would locally mound abovethe surface. The soil adjacent to the fracture would eventuallybecome cemented by calcium carbonate. This would result in arelatively dense material that would be stronger than the partly­or non-cemented soil out some distance from the fracture. Thedifference in compressibility might allow the growing ridgeeventually to tilt outward and down as two halves along a hingeline medial and parallel to the base of the ridge. In someexamples only one side would tilt. in others. both sides.

Horizontal separation of as much as 20 inches occurred inthe medial fissure in growth units one and two of the thirdsegment of Hot Tub Ridge. The fissure-forming mechanism

was in all probability theresult of hydrostatic and crys­tallizing pressures producedby ascending supersaturatedthermal waters.

Photo 7. View looking southwest along media! lissure insegment three of Hot Tub Ridge. Maximum ridge separationhere is about 30 inches. The inner terrace on the north wall,partly in the shadow in the center of the photograph, isseparated from the OpPOsite inner terrace by the inner fissure.Pick on inner terrace has a 12-inch handle.

Ridge Formation

Opening 01 the Fissure

Hot Tub Ridge developedalong a relatively long fracture.The principal fissure that led tothe development of Hot TubRidge probably opened at thenortheastern end of each ofthe three segments that com­pose the ridge. The short seg­ment at the northeastern endof the ridge was first to de­velop and probably becameinactive prior to the openingup of the source fracture of themiddle segment. Similarly, themiddle segment of Hot TubRidge probably ceased to de­velop prior to the opening upof the source fissure at thenortheastern end of segmentthree. Each segment probablyextended itself in a southwest­ward direction by the emer­gence of hot mineralized waterfrom the bedrock fracture as itcontinued to open andlengthen towards the south­west.

As illustrated by the descrip­tion of Hot Tub Ridge, it isdear that fractures in the bed­rock played an important rolein the development of thefissure ridges. and even thefissure mounds. The originaland principal role of the frac­tures was to act as conduitsalong which calcium bicarbon­ate waters moved to form theridges and mounds.

CALIFORNIA GEOLOGY AUGUST 1991

SEQUENCE OF EVENTS

Photo 8. Mini·terraces of calcareous mush developing on gently sloping soil'coveredsurface in southwestern part of thermal area. scale is indicated by the 12-inch pickhandle.

We believe that a travertine terrace at Travertine HotSprings was likely to have been the first result of spring depo­sition and that the process is continuing today. Such featuresas pools and mounds have come and gone in the overallevolution of the deposits of the hot springs. Studies of theapparent overlapping mound and ridge travertines have re~

vealed the stratigraphy of the deposits and the sequence oftheir formation (Chesterman and Kleinhampl, in prepara­tion). Other ridgesand mounds mayhave developedalmost simulta­neously, but sev­eral of these fea­tures are isolatedfrom one another.Their flanks arepartly or com­pletely overlain byterrace travertineso their actualsequential relation­ships are difficultto deduce.

Rate of TravertineDeposition

The numberand rate of growthof crusty layers ofindividual fissureridges are notknown so theycannot be used toestimate thelength of timeinvolved in ridgedevelopment. In the southwestern part of the area, near thesite of early quarrying operations, one can find small terracesbeing formed today (photo 8). These small terraces. or mini­terraces, are composed of calcareous mush. They were not inexistence in 1983 but others were forming elsewhere in thearea at that time. In October 1985 the mini-terraces hadwidths (front rim to back) ranging from 1/4 to 3/4 inches.On the basis of a 13-month period of development. the rateof calcium carbonate deposition ranges between about 0.02and 0.06 inches per month. The mini-terrace material isquite fragile and porous and evidently developed at a rela­tively rapid rate. Although the fissure ridges and mounds alsoconsist largely of porous travertine. they may not have devel­oped as rapidly as the minHerraces.

MINERALOGY AND GEOCHEMISTRY

The spring deposits at Travertine Hot Springs consist al­most entirely of travertine. Siliceous sinter. which occurs atSteamboat Springs. Washoe County, Nevada and other hotspring areas in the western United States. was not found.However. there is a sticky and slippery feel when walking on

the wet terrace surface which indicates that clay may be ad­mixed with some of the wet crystalline mush being depositedon the terrace surfaces. A relatively pure-looking white stickyclayey substance is forming around the orifice of one of thehottest springs (a rare occurrence). This substance was foundby Paul Russell to contain chiefly calcite, minor quartz, and aminor amount of illite (oral communication. 1984). A minoramount of illite may be admixed with some of the porous

travertine else­where in theterraces, but thetravertine wasnot analyzed forclay.

Springs

The chemicalcomposition ofsome of the hot­test waters atTravertine HotSprings has beendetermined and itappears that thesewaters must havea large meteoric(derived fromrainwater) compo­nent (Chestermanand KJeinhamp1.in preparation).The presence oflithium in thespring waters mayindicate the exist­ence of a mag­matic component.

They have at least passed through. if not originated in. a car­bonate rock terrane judging by the large amount of carbonatedeposited at the site.

The surface of the ground, as well as the blades of grassand other prostrate forms of vegetation. is quite heavily cov­ered by a coating of white pulverulent sodium bicarbonate(Photos 2 and 3). This substance precipitates from springwater and from groundwater that rises to the surface.

COMPARISON WITH OTHER HOT SPRINGS SYSTEMS

There are a number of places in the western United Stateswhere travertine has been deposited. Although the calcareousmaterials deposited in some of these places are similar inmany respects to the travertine at Travertine Hot Springs.they may have developed under different sets of physical con­ditions. As mentioned previously, the travertine deposits atTravertine Hal Springs developed on a land surface whenascending supersaturated bicarbonate waters lost carbon diox­ide to the atmosphere, enabling the calcium carbonate toprecipitate as calcite. [n contrast. the lufa deposits (tufa cones)

(Continued on page 182 ...)

CALIFORNIA GEOLOGY AUGUST 1991 '"

A Page For Teachers

The Simplified Geologic Map ofCalifomia was compiled by the

Division of Mines and Geology (DMGland the United States Geological SUlvey(USGS). Geologic maps show thedistribution of different types and agesof rocks with the use of colors. Latitudeand longitude lines, the north arrow. thebar scale, and the locations of majorcities and geographic features provide areference system.

The explanation on the right-handside of the map lists the rock typesincluded in each color-coded map unit.Contacts are shown as thin black linesseparating map units. Faults. shown asthick solid or dotted black lines, areplanes or zones of movement betweenvery large blocks of rock.

There are three major types ofrocks-igneous, sedimentary, andmetamorphic:

1. Igneous rocks fonn by the cooling of molten (hot liquid) rock. Igneous -"""'\~~":o~~~~~rocks are divided into two broad groups. The first group. made up of igneous l~rocks that fooned at the surface. are called extrusive or volcanic rocks. Basaltand pumice are volcanic rocks. The second group. made up of igneous rocksthat fonned slowly from the cooling of magma deep in the Earth's crust, arecalled intrusive or plutonic rocks. Granite and gabbro are examples of intrusiverocks.

2. Most sediments and sedimentary rocks are composed of pieces of, orgrains from. pre-existing rocks. These fragments may range in size fromboulders to sand to sub-microscopic clay particles. Most have been movedaway from their source by water, wind. or ice and deposited in Oat layerscalled beds. Conglomerate. sandstone. and shale are examples of sedimentaryrocks. Other sedimentary rocks form by precipitation from seawater or othermineral-rich waters. Limestone. salt. and gypsum are examples of this specialtype of sedimentary rock.

3. Metamorphic rocks are formed by recrystallization of pre-existing rocksas a result of heat and pressure from many kinds of geologic processes. Mostof these processes are related to the movement of massive plates of theEarth's crust. Marble. slate. schist. gneiss. and greenstone are metamorphicrocks.

The rocks of California are divided into two groups: the intrusive igneousrocks, and the sedimentary and volcanic rocks. The metamorphic rocks areincluded with the sedimentary and volcanic rocks because for the most partthey are the metamorphosed equivalents of these rocks. The rocks are placedin the order of foonation: the oldest at the bottom. successively younger unitsabove. Map units shown at the same level in the explanation are about thesame age.X

'"0 CAliFORNIA GEOLOGY AUGUST 1991

S10IME"-'111RY AND VOLCANIC 'KX:KS

EXPLANATION

CtnQ,O<C rn.""""",,,.,.,nl• ..,. mck<

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ute Mew,,,,,, (I.,O'S' Jur•..oc.ndC""<>c"""'l eUi"""'vneliNI rocks

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Oftl"n~I'ry rock.

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SimplifiedGeologic Mapof California

Me>o.looc ""',menl."! and voIc.n"'ock, <>Ider ,h.n I.... N""~.n or"8f'ny;

In pi..," Iltorlg'l M("Iomo,p/IosN

li'o'lRUSIVE IGNEOUS ROCKS

P"",amo"," rod, of .lItyll'" 'ncllld,ng(oo~r.,ne-d ,nuu",,,,,

Pre-<:enozoic mel,"""""", rock.01 unkrlOWn age

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CALIfORNIA GEOLOGY AUGUST 1991 '"

(... Continued from page 179.)

exposed along the north and southshores of Mono Lake, Mono County,California. developed below the surfaceof the lake waters principally as the re­sult of cold spring water welling upthrough and interacting with the lakewater.

Steamboat Springs

Steamboat Springs is situated in Ne­vada approximately 80 miles northwestof Travertine Hot Springs. Althoughthese two thermal areas have severalfeatures in common. one of the principaldifferences is that the material beingdeposited at Steamboat Springs is sili­ceous sinter, consisting of several silicaminerals including opal and chalcedony.and minor quartz (White and others,1964). Minor amounts of travertine aredeposited near certain springs, but be­cause of the appreciable sulfuric acidcontent of the spring water, the traver­tine dissolves and is also readily removedby weathering. There are terraces, fis­sures. springs, pools, and geysers thatdischarge intermittently hot or boilingwater at Steamboat Springs. Prominentfissure ridges. which are so common atTravertine Hot Springs. are absent atSteamboat Springs. Cinnabar. pyrite.and stibnite have been found in the sin­ter at Steamboat Springs. These metallicminerals have not been observed atTravertine Hot Springs.

Elise MattisonJoins California

Geology Staff

Geologist EliseMattison has joined thestaff of CALIFORNIAGEOLOGY as a techni­cal editor. She is agraduate of CaliforniaState University,Sonoma and waspreuiouslyassigned tothe Diuision's AppliedGeophysics Program.X

Mammoth Hot Springs

The spring deposits at Mammoth HotSprings. YelloVJStone National Park.Wyoming, are comparable in many re­spects to those at Travertine HotSprings. In fact. the resemblance be­tween them is striking. The main geo­morphic features at Mammoth HotSprings include hot spring cones. caves.tension fractures. collapse features. spec­tacular terraces and fissure ridges. TheTravertine Hot Springs area is quitesmall, only about 9 acres, as comparedwith Mammoth Hot Springs, which em­braces more than 550 acres.

ACKNOWLEDGMENTS

The authors wish to thank severalmembers of the geological staff of theCalifornia Division of Mines and Geol­ogy in Sacramento, California for theirmany useful comments, especially to Dr.Rodger H. Chapman for his kind andcontinuous encouragement in this work.Thanks also are extended to Dr. WilliamC. Bagby (U.S. Geological Survey.Menlo Park, California) who criticallyreviewed the unabridged manuscript(Chesterman and Kleinhampl, in prepa­ration) during its late stages of prepara­tion.

REFERENCES

Allen. E.T., and Day, A.L., 1935, Hot springsof the Yellowstone National Pal1o;:Carnegie Institute of Washington,Publication No. 466. 525 p.

Bargar, K. E., 1978. Geology and thermalhistory of Mammoth Hot Springs,Yellowstone National Pal1o;. Wyoming:U.S. Geological Survey Bulletin 1444.53p.

Chesterman, C.W., and Gray, C.H., Jr.,1975. Geology of the Bodie quadrangle.Mono County, California: CaliforniaDivision of Mines and Geology. MapSheet 21, scale 1:48.000.

Chesterman. CW., and Kleinhampl, F.J., inpreparation, Travertine Hot Springs atBridgeport. Mono County, California:California Division of Mines and GeologySpecial Report 172.

Russell. Paul. 1984. oral communication.

White, D. E., Thompson, G.A., andSandberg. C.H., 1964, Rocks, structureand geologic history 01 SteamboatSprings Thermal area, Washoe County.Nevada: U.S. Geological SurveyProfessional Paper 458-B, 63 p.X

'" CALIFORNIA GEOLOOY AUGUST 1991

MaripositeThe Rock That Made California Famous

. . . . . . The Rock Across America Project . . . . ..By

GEORGE W. PEABODYHistorian, EI Dorado County Committee on the Bicentennial altha

U.S. Constitution, Placerville. EI Dorado County, Calilornia

DESCRIPTION

So the beautiful mottledgreen and white mariposlterock was selected to repre­sent California in theFountain of Freedom-The Constitution Monument.

property of Eugene andCathy Barnett (Photo I).The Barnetts donated themariposile boulder for usein the monument. With thisgift. serpentine lost to theharder. more weather­resistant. gold-bearingmariposite rock.

Occasionally marlpositerock contains networks ofgold-and iron sulphlde­bearing quanz velnlets andstringers (Kistler and others.1983) (Photo 2). Mariposlterock consists of the mineralmariposlte (a bright applegreen chromium-rich mica)with a white groundmass offine-grained glassy quartz.Several carbonate mineralsare present In some speci­mens. In 1868. BenjaminSilliman. Jr. collected asample of mariposite fromthe Josephine mine (Figure1) and named It for MariposaCounty. California. Sincethen, it has been identified

throughout the Mother Lode of theSierra Nevada (Murdoch and Webb.1966) and in other locations around theworld. Today, gold is still mined frommariposlte-bearing ores at severalMother Lode localities.

Wheeklon located an outcrop of maripo­site 4 mlles upstream Irom Colomawhich may have produced that gokl.The outcrop can be seen from the headof Big Canyon. nonh of Placerville andeast of Highway 193. Several bouldersfrom the outcrop were found on the

Photo I. Eugene Barnett with the donated mariposite rockat Big Canyon in Placerville. California. August. 1987.Photo by Chef Ansley.

The El Dorado CountyComminee on the

Bicentennial of the UnitedStales Constitution acceptedthe assignment to select anddeliver California's rock foruse in the monument.

"The committee's firstnomination was serpentine,California's State rock.However. local geologistGeorge A. Wheeldon recom­mended that mariposite. arock associated with serpen­line, be selected to representCalifornia at the Fountain ofFreedom.

Wheeldon also searched for thesource of the gold that touched off theCalifornia Gold Rush. On January 24.1848. James W. Marshall discovereda gold nugget in the tailrace of JohnSutter's sawmill at Coloma. on theSouth Fork of the American River.

July, 1987 Wanted:one 1O,SOO-pound rockto represent the GoldenState of California inPhi/adelphia's <;Fountainof Freedom - TheConstitution Monument"celebrating the 200thanniuersary of the UnitedStates Constitution andthe Bill of Rights, to bedelivered to Phi/adelphia,Pennsyluania by Septem­ber 17. 1987, the bicen­tennialof the signing ofthe U.S. Constitution.

CALIFORNIA GEOLOGY AUGUST 1991 '"

USES AND STATISTICS OF MARlPOSITE

Mining: Gold ore.

Lapidary: Cabochons, book ends, paper weights, headstones,ornamental objects (Sinkankas, 1968).

Color and luster: Apple green, white (Murdoch and Webb, 1956). Emeraldgreen, apple green (Knopf, 1929).

Mode of occurrence: Abundantly distributed in the Mother Lode gold belt ofthe Sierra Nevada, foliated in an assemblage knownas mariposite rock. (Knopf, 1929; Considine, 1988).

Environment: Found in schist, as nests and tenses in talc-sericiteschists (Murdoch and Webb, 1966). Also found innarrow zones to broad belts in association with quartzand carbonate minerals such as ankerite, dolomite ofmagnesite, and resulting from hydrothermal alteration ofserpentine (Considine, 1988).

Composition: Variety of muscovite. Basic potassium aluminumchromium silicate. (Murdoch and Webb, 1966).

Crystal form: Monoclinic. In hexagonal plates and scales, foliated,micaceous (Murdoch and Webb, 1956).

GENESIS

Mariposite formed when serpentinewas altered under pressure by mineral­laden hot (650"F) water. The water.containing potassium, silica, carbon,oxygen. and other elements. flowedupward from sources deep in theEarth·s crust along fractures, faultsand fissures in the rocks. When thesehydrothermal fluids reacted with theserpentine. they formed deposits ofquartz, chromium-rich mica. sulphides.and occasionally gold. At that timethese rocks were completely hiddenunder the surface of the Earth. Theancestral Sierra Nevada began to rise100 million years ago (Hill. 1975) andthe rock above the mariposite slowlyeroded. The rich veins were exposedabout 45 million years ago (Norris andWebb, 1990). Continued erosionreleased the gold from the rock. andstreams carried it dov.m the slopes.

Mariposite rock and the variedquartz and gold veins are found alongthe Mother Lode's Melones fault(Kistler and others, 1983; Bohlkeand Kistler, 1986; Evans and Bowen.1977) which separates the PaleozoicCalaveras Complex phyllite from theLate Jurassic Mariposa Formationgraywacke and volcanic rocks (Loydand others. 1983).

Photo 2. Mariposite rock. 7 l( 6 l(

2.5 inches. Photo by Max Flanery...

Optical properties:

Hardness:

Luster:

Specific gravity:

Cleavage:

Habit:

Straight extinction and positive elongation, opticallynegative, of narrow axial or uniaxial angle. Index ofrefraction: alpha = 1.56 to 1.58, gamma = 1.61 to t .63(Knopf, t 929); beta::: 1.624 (Deer and others, 1962).

2.5 - 3 (Murdoch and Webb, 1956).

Vitreous (Murdoch and Webb, t 956).

2.78 - 2.81 (Murdoch and Webb, 1956).

Perfect basal (Murdoch and Webb, 1956).

Green plates and flakes. tabular (Murdoch and Webb,1966). Foliated, micaceous.

ACKNOWLEDGMENTS

Eugene and Kathy Barnett fordonating the mariposite boulder.

Lester Lubetkin, geologist. U.S.Forest Service. technical editor for thismanuscript.

George A. Wheeldon. geologist,George A. Wheeldon & Associates.Geological Consultants, for locating themariposite boulder and suggesting its usein the monument, and for assisting inediting this manuscript.

'" CALIFORNIA GEOLOGY AUGUST 1991

BOhlke, J.K. and Kistler, R.W.• 1986, RIrSr,K·Ar, and stable isotope evidence for theages and sources of fluid components ofgold-bearing quartz veins in the northernSierra Nevada foothills metamorphic belt,California: Economic Geology, v. 81,p.296-322.

Calilomia Division of Mines and GeologyDMG Note 10: Chrysolile asbestos andserpentinite in California.

l . TEHAMAM~NDOCI~,\--'.--__(

t,1

Deer, WA, Howie, A.A.. and Zussman, J..1962, Sheet silicates, muscovite: Rock­forming Minerals, v. 3, John Wiley & SonsInc., p. 11-30.

Evans, A.E. and Bowen, O.E., 1977,Geologic map and sections of thesouthern Mother Lode, Tuolumne andMariposa counties. California: CaliforniaDivision of Mines and Geology, MapSheet 36.

Hill, M., 1975, Geology of the Sierra Nevada,California Natural History Guide 37:University of California Press.

Kis!ler, A.W., Dodge, F.CW., andSilberman, M.L, 1983, Isotopic studies ofthe mariposite-bearing rocks from thesouth-central Mother Lode, California:Catifornia Geology, v. 36. #9, p. 201·203.

Knopf, A., 1929, The Mother Lode system 01California: U.S. Geological SurveyProtessional Paper 157, p. 38.

loyd, R.C., Anderson, T,P" and Bushnell,M.M., 1983, Mineral land classification ofthe Placerville 15' quadrangle. EI Doradoand Amador counties, California:California Division of Mines and GeologyOpen-file Report 83-29 SAC, p. 8-13,25-26.

MitchelVGiurgola Architects, 1989, Fountainof Freadom - The Constitution Monu­ment· schematic report: U.S. Departmentof the Interior, National Pari<. Service,14 p.

Murdoch, J. and Webb, A.W.. 1956, Mineralsof California: California Department 01Natural Resources Bulletin 173, p.219·220.

Murdoch, J.. and Webb. A.W.. 1966,Minerals 01 California: CalilomiaDepartment of Natural ResourcesBulletin 189, 256 p.

Norris, A.M. and Webb, RW., 1990,Geology of California. second adition:John Wiley & Sons, New Yorl<., p. 74,84-86, 108.

Rice, S.J.. 1957, Asbestos. in Wright. L. A.,ed., Mineral Commodities of California,California Division of Mines Bulletin 176,p.49·58.

Rice, S.J., 1957, Chromite, in Wright, LA,ed., Mineral Commodities of Calilornia,California Division of Mines Bulletin 176,p,121-129.

Sinkankas, J.. 1968, Van Nostrand'sStandard Catalog 01 Gems: VanNostrand/Reinhold, New York, p. 78.

Skinner, H.C.W" Ross, M., and Frondel, C.,1988, Asbestos and other fibrousmaterials: Mineralogy, Crystal Chemistry,and Health Effects: Oxford UniversityPress, 204 p.

Wicks, F.J. and O'Hanley, D.S" 1988,Serpentine minerals: Structures andpetrology, in Bailey, SW., ad., Mineral­ogical Society of America, Reviews inMineralogy, v. 19. p. 91-167.:-t

.... Figure 1. Map of California showing principalserpentinite occurrences. Modified fromCalifornia Division of Mines and GeologyDMG Note 10.

LASSENMODOC

Clark, W.B., 1957, Gold, in Wright, L.A.,ad., Mineral Commodities 01 California,California Division of Mines Bulletin 176,p.215-226.

Considine, K. A" 1968, Hydrothermalalteration at the Pacific mine, Placerville,EI Dorado County. California: M.S. thesis,University of California, Davis, 37 p,

SHASTASISKIYO

REFERENCES

OREGON

. -TRINtT

,,

Serpentine/peridotiteoutcrops (Rice. 1957)

Gold bearing areaof the Mother Lode(Clark. 1957)

'" Melones fault zone" and Mother Lode Belt

(Clark. 1957)

•D

CALIFORNIA GEOLOGY AUGUST 1991 '"

'86

-

CALIFORNIA GEOlOGY AUGUST 199\

Division of Mines and GeologyBay Area Regional OfficeReturns to San Francisco

INTRODUCTION

The new office is close to Federal and State buildings andCity Hall (Figure 1). It is accessible by various types of trans­portation including BART and Muni Metro via the Civic CenterStation. Market Street exit. There is also easy access fromHighway 101 with convenient parking at Civic Center Garageand several other local lots.

HISTORY

Originally established by the State Legislature in 1880 asthe Stale Mining Bureau. DMG has a long history in the city ofSan Francisco, From 1880 to 1898 the State Mining Bureauoccupied various office locations in the city. In 1899 theoffices were moved to the newly constructed Ferry Building atthe foot of Market Street (Photo 2). Although DMG headquar­ters was transferred to Sacramento in 1970. an office re­mained in the Feny Building until renovations forced reloca­tion. The Division offices opened in Pleasant Hill in 1984 andremained there until now.

The Bay Area Regional Office of the Division of Mines andGeology (DMG) returned to San Francisco on August 12th.

1991 after 7 years in Pleasant Hill, Contra Costa County. Thenew location is 1145 Market Street (Photo 1), between 7thand 8th streets, directly across from United Nations Plaza.

....;••11i

i~;;:::: ,..--____ '•......_- , .

-- -<'''."••I... ', , •,.

II

Photo 1. One Trinity Center. at 1145 Market Street In SanFrancisco. is the new home 01 DMG's Bay Area Regional Office.

DESCRIPTION OF FACILITIES

As the stale geological survey ofCalifornia. DMGs primary role is toprovide State and local governments.the private sector. and the public withearth science information thai will assistthem in making wise land-use and otherpolicy decisions.

The Bay Area Regional Officeprovides geological information to 17counties in northern and cenlralCalifornia. It is currently staffed by lentechnical and support personnel. It Isanticipated that expansion of the newlyestablished Seismic Hazards MappingProject will add additional technical staffto this office over the next several years.A 2,000-square-foot staff/referencelibrary and an infonnation and publica­tions sales counter are available to thepublic.

Photo 2. The Ferry Building, located at the foot ot Market Street in San Francisco. housedthe offices of OMG (previously the State Mining Bureau) from 1899 until 1984.

CALIFORNIA GEOLOGY AUGUST 1991 ",

BUILDINGS

1. Division 01 Mines and Geology1145 Market StreetSan Francisco. CA 94103-1513Office (415) 557·1500Ubrary (415) 557-1629

E - Embarcadero StationM . Montgomery Street StationP . Powell Street StationC - Civic Center Station

$C.LE

BART/MUNI METRO STATIONS

',"",';;"':'.'"'~'''':':'_'~''- ''''''n .,...

'"

>

", , '.~.e.

"-.,",,""'"

" f~.....,... " N,I

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14. Ferry Building

12. U.S. Forest service630 Sansome StreetSan Francisco, CA 94111(415) 705·2674

13. U.S. Geological Survey504 Custom House555 Battery StreetSan Francisco, CA 94111(415) 705-1010

11. TransbayTermlnal

10. Moscone Convention Center

7. Federal Building

8. Brooks Hall (undergrOUnd)

6. San Francisco Main Ubrary

9. Civic Auditorium

2. Federal BuildingGPO Bookstore450 Golden Gate AvenueSan Francisco, CA 94102

3. State Building

4. State Building

5. San Francisco City Hall

Figure 1.locatlon of DMG's new Bay Area Regional Office and otherbuildings around Civic Center and downtown San Francisco.

The Bay Area Regional Officesupports two major DMG programs­the Geologic Hazards Program and theGeologic lnfonnation and SupportProgram.

GEOLOGIC HAZARDS PROGRAM

landslide Hazards Identification Project

The Landslide Hazards IdentificationProject staff produce maps that provideinformation about slope stability inurban and rapidly urbanizing areas.These maps assist local governments inmaking Jand-use decisions that winreduce property loss due to landsliding.

The staff members have preparednine Landslide Hazard IdentificationMaps of selected areas in central andnorthern California. These areas include:Petaluma Dairy Belt (Sonoma County);parts of Diablo and Dublin [7.5'J quad­rangles (Contra Costa County); Benicia­Vallejo area (Solano County); south·halfof Fairfield North [7.5'1 Quadrangle(Solano County): Cordelia-Vallejo area(Solano and Napa counties); Vacavilleand vicinity (Solano County); Clear Lakeand vicinity (Lake County); Cache Creekarea (Lake, Yolo. and Colusa counties):and livennore Valley and vicinity(Alameda and Contra Costa counlles).

Fault Evaluation and Zoning Project(Alquist-Priolo. A-P)

The Fault Evaluation and ZoningProject staff prepare maps that delineatezones around active and potentiallyactive faults throughout the State. Thesemaps help local governments regulatedevelopment within these "SpecialStudies Zones~ in an effort to protectthe public from the hazards of surfacefault rupture.

Approximately 100 Special StudiesZone maps have been issued for thosefaults in the Bay Area considered to beactive or potentially active as defined bythe State Mining and Geology Board.

,sa CALIFORNIA GEOLOOY AUGUST 1991

SPECIAL REPORTS__SR106 Geologie features of Death Valley 11010 afld San BemaldlJlo coumiesl.

Cahtomia.1976...................... . $5.00__SRl 13 GIlOIogk: hazards 10 southwestem Sao Bemald400 County. Califomia. 1976 $\ 7.00

I TOTAL AMOUNT ENCLOSED _ 5 _

1 PAYMENT MUST BE INClUDED WITH ORDERL _

SPECIAL PUBLICATIONS__SP50 Colemafllte depo$Its near Kramer JuncliOl'l. Sao Bernardioo County,

Califorl'\la.1976 . $5.00__SP72 MII'lOral commodIty report· gypsum. \984 $5.00__SP74 Mineral commodity report· sulphur. 1984 . $5.00__SP76 Minerai commodity report· bame 1985... $5.00__SPl II Minerai commodity report - diatomlle 1991 (NEW) 5500

,----------------------------MAIL ORDER FORMComPete address form Ol'l next page.

Indicate number Pnce includesof copoes. postage and sales lax.

•BUUETINS__B183 FraflClSCan and related rocks and their SI(ll'\llieance io !he gooIogy ot

wesllmCaIilomia 1964 . $8.00__B195 Geology ot lhe Sao Andreils 115·1 quaoraflgle. CalaVlfas Couoty.

California (scaJe. I :G2,500). 1970.. . $5.00__6206 Geology and ore deposits ot the Bodie mlJllflg dislnct. Mooo County.

Califomla. 1987... . $18.00

$10.00

"" 00"25

LOCATION AND HOURS

The new address is;

Department of ConservationDivision of Mines and Geology1145 Market Street, 3rd RoorSan Francisco. CA 94103-1513Office; (415) 557-1500Ub<a<y, (4151557-1829

CONCLUSION

DMG's return to San Francisco offerseasier access to its constituents. therebyincreasing public contact and improvingawareness of its programs and functions. )I'

Hours lor the office and library are8:00 to 5;00 Monday through Friday.Visitors should be prepared to Slgn inand out at the security desk.

..................................~.............. 55.00................................................................... 55.00

................._, _ 55.00..........................................._........... _.55.00

GEOLOGIC MAPS OF CALIFORNIA - REPRINTS__GAM 4 Death Valley $hie'

GAM 5 Fresno sheet__GAM8 LosAngele$ sheet__GAM9 Maf1XlSl sheet

CALIFORNIA GEOlOGY__ 1 year (121SS08S)_2 years (241SSUl1$)..... ....-

Sp9afy IIOIl.olN and monlh

Lisl 01 A...adable PublicalIOnS

Aside from \lIOTking on normal day­to-day project assignments, the librarystaff respond to public inquiries thatrequire specific technical answers andrepresent DMG at professional meet­ings. 'They also provide community andeducational outreach 5eTVice:s such asparticipation in career days. job fairs,and geology club meetings at localschools and universities. 1bese contactshelp keep the public and the scientifICcommunity aware of DMG activities,

with earth science-related subjects. Acomputer data base of DMG's libraryhokiings. as well as access to theMELVYL system of State Uhraryholdings, provides users with powerfulbibliographic search capabilities. Eachyear approximalely 1.700 people usethe library.

Geologic In/ormation andPublications Project (GIPP)

This project disseminates geologicinformation and sells DMG publications.G1PP staff handle routine inquiries and,when necessary, route technicalquestions to appropriate DMG person­nel. Information staff in the Bay AreaoffICe respond to approximately 4,200telephone calls and in-person publk:contacts annually.

library 5eMces PrOject

DMG's Bay Area library providesstaff members and the public withbooks, perkxljeals. maps, and unpub­lished theses and dissertations dealing

GEOLOGIC INFORMATIONAND SUPPORT PROGRAM

ReglOflal GeologIcMapping Proteet (RGMP)

The RGMP staff prepare smail-scale(l:25O.000 and 1:750,000) statewklegeologic maps and intermediate-scale(l; 100,000) maps of selected urbanareas. A new San Francisco - San Jose1:250.000·scale quadrangle is In pressand the Monterey 1:100.00Q-scaJequadrangle is being prepared. A new1:750.0QO-scale fault activity map ofCalifornia is also in preparation. OtherRGMP functions include the preparationof indexes of geologic maps andgraduate theses and dissertations. Also.an extensive collection of published andunpublished geologic maps Is alsomaintained. RGMP products are oftenthe starting points for many types ofgeologic investigations such as mineralresource and geologic hazards assess­ments.

These include the San Andreas,Hayward, Calaveras. Greenville. GreenValley, Concord. Antioch, SanGregorio, Rogers Creek· Healdsburg,and Maacama faults.

Urban seISmic HazardsMapping Pro;ecl

The newly established Urban SeismicHazards Mapping Project provides localgovernments with maps that delineateand classify those areas that may besusceptible to earthquake-inducedground faihJres and amplified strong

ground motion.

CALIFORNIA GEOLOGY AUGUST 1991 '89

GSA Holds Annual Meeting in October 1991

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contamination constitule a number of themesessions. Case studieS wiU be presenled, andremediation techniques for coniaminated soiland groundwater will be addressed. YuccaMountain. being considered for lhe nation'sfirst potential underground repository forhigh-level nuclear ",<'ISle. will be lhe sub;ect ofone of these lheme sessions.

• Resources: The Costs and Con__quences of Use addresses one 01 lhe masldiffiCult and challenging socioscientifiC issuesof our time: eslimating the magniludes.local ions, and a«:essibility of variousresources. lhe costs of recovering andusing them. and the possible environmenlalconsequences of doing so.

• Predicting Our Future; How GoodAre the Models? discusses present models.which prroict an unsuslainable population of10-15 billion. causing disastrous effects, if thepubliC does not act to preserw our plane!. Dolhese models adequalely prroict probableglobal circumstances. and how can we adjustto expeclro effects?

• Urban Geologtc Hazards include r'IOlonly natural hazards but also those lhat occurafter development. This session spotlights lheevaluation of geologic condilions prior to.during. and after development In urban areas.

• Venus and Earth; Tectonic andVolcank: Evolution presents results lromthe Magellan spacecrah ....oyage and hypoth·eses concerning the intemaJ and externalevolution of Venus and Earth. Informationgained about Earth's sister planet Venusshould shed light on studies of lhe euoIution ofEarth. as both planets have similar size.density. and position in the solar system.Another session on pl;.tnetary geology. NewViews of the Moon. discusses results fromthe Gallleo mission.

• GeoRisk Assessment examines ways10 assess risk 10 human health and welfareIrom geologic hazards and how to lransmitthis information 10 the public.

• Coalbed Methane Geology andRecovery focuses on the recovery of naturalgas producal from coal seams (coalbedmethane). Coalbeds in the Unilal Slates areestimatro 10 contain more than 400 trillioncubic feel of melhane.

In addition to lhe technical sessions. 30fIeld trips and 13 short coun;es will be offered.A 250·booth exhibit hall will feature state.of­the'an equipmenl and services. liS wen ascurrent educational resources and programs.and the lalest publicalions and maps. Anongoing science theater will present manyinformative and colorful programs onvolcanoes. dinosaurs. earthquakes, mountainbuilding. and other topics 01 broadergeological interest.

For more infonnation conlact:

sandra RushGSA Communications Depanmenl(303) 443-8489 y

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America investigates the arid and semiaridparts of the nation, which aTe among some ofthe most climatically sensitive regions on thecontinent. A better underslanding 01 howclimate has variro in these drought-proneregions during past geologic time (to 30.000years ago) is important lor lhe prediction ofclimatic change and the potential effect ofglobal wanning.

• Geology of the Padflc Rim addressesthe geology 01 Japan and seiSmOlogy of thePacific plate. This symposium sets the stagefor the 29th Intemational GeologicalCongress in Japan in 1992

• The Cretaceous·Tertiary (KIT)Boundary. "The first session addr~ thevalidity of the hypothesis that the impacl ofan asteroid collision wilh Earth is linked 10 theexlinction of dinosaurs and Olher life fonns."The second of these sessions fOC\l!iol.!s on thenonmarine fossil record (both pl;.tnt andanimal) of 66 mUlion years ago to assesswhether extlnclion was caused by II cat".strophic event or was the result of gradualevoIutK>nary processes.

• Hcuardous Waste Site Charactema'lion Studies relatro to soil and groundwater

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~Global PerspectiveM will be the themeof this year's Geological Society of America(GSA) meeting in San Diego, California.October 21·24. 1991. Emphasis wiD be ongIob;lI change. natural disasters, and theUmlts of natural resources. Presentations willfocus on Earth illS a whole, and discu&SiOnSwill involve solutions to our major environ­mental problems. San Diego State Universityand lhe San Diego Associatm of Geologistswill host this rTlei!ting al the new San DiegoConvention Center. More than 6.000geoscientists from around the globe areexpected to attend.

TIle following are some ollhe ledlOicaJsessions at the meeting:

• Global Climate Change is II two-parttheme session. The first part presents theglobal record of climate dynamics. focusingon the data and methods of analysis thatallow earth scientists to reconstruct whathappened CNeT lime frames of years tomilliOnS of years. The second part of thissession is based on the premise that thegeologic past can be II key to the geologicfuture. 1he symposium QuaternaryClimaltc Change in Western North

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'" CALIFORNIA GEOLOGY AUGUST t99\

Call For Photos Response

These photographs of the geologic splendor of Califomiawere submitted in response to CAUFORNIA

GEOLOGYs "Call For Photos:'

We encourage you to submit color geologic photographslor publication in future issues of CAUFORNlA GEOLOGY.

A stipend of $25 will be paid for each photo used inCAUFORNIA GEOLOGY.

The term trondh)emlte was first used formally byV.M. Goldschmidt in 1916 in his study ollntrusivesof the TrOndhjem. or Trondheim, area of Norway. II isaccepted as an oHicial name for a very light-coloredplutonic rock thai consists largely of sodic plagioclaseand quartz with only minor amounts of biotite ancllinleor no potassic feldspar. Trondhjemite is interestingbecause jts occurrence is often indicative of incorpor­ation 01 oceanic crust with continental crust.

SEND IN YOUR COLOR PHOTOGRAPHS ANDSHARE THE GEOLOGIC WONDERS OF CALIFORNIA.

Castle Dome (left) and snow-covered Mt. Shasta (right). Castle Crags Stale Park, near Castella. Shasta County. California. CastleDome is composed of Jurassic (162 to 175 million years old) granodiorite and trondhjemite (see above). lis shape is due to jointingand to the process of exfoliation (see page 192). Ml. Shasta (14,162 feet) is California's largest volcano. Kodachrome-64. 35mmlens. 1/125, fill. Photo by James W. Car/bJorn.

CALIFORNIA GEOLOGY AUGUST 1991 '"

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(From Cover) The bald, rounded surlaces 0' most gramtic domesare the results of a process calkld exfoliation. Differenlialstresses WIthin the rock cause it to peel ott In curved slabs. Therock expands and breaks when confining lorces are reduced asupllh and erOSIOn bring once deeply burled rock masses to thesurlace Variabons in humidity and temperature. and the slowdevelopment and expansion 01 clay minerals by near·wrfacechemcaI weathering may be laetors in this process.

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(BelOw) The serrale mOl,mlaln ridge calkld The Minarets is anexample of an arele rllSh bone" in French). Compacted snowaccumulates above the snow line. recrystallizes into glacial ice.and sIowty tIows downslope. An amphitheater-shaped hollOw(Cirque) t()(fT1S at the head 01 a glacier as the mass 01 mow-.g icecarves a valley out 01 tho mountain along its course An arAteresults when two cirques or two rows 01 cirques Iorm back·to-back.The rocky dMde cut berween two paraDe! glaaated valleys mayalso be calkld an arAte.

The Mmarets (12.281 feet) and Minaret lake. Ritter Range, Inyo National Forest. Calilomia. The Minarets are strikll-.gly jagged because!hey projected above the llow of Pleistocene gladers. 1000000ng an .rite (see above). Their unique craggy spires are due pnmarily towedging caused by the treezing and thawing 01 water along venal surface tractures (joints). Kodachrome'54, 35mm lens, 1/125.111",6. Photo by James W. CarlbkJm. x

", CALIFORNIA GEOLOGY AUGUST 1991