CALIFORNIA

GEOLOGYA PUBLICATION OF THE

OEPARTMENT OF CONSERVATIONDIVISION OF MINES AHO GEOLOGY

$Ial. ol cald_ PETE WlLSON

""""""Tho!~ Ag«lcy DOUGLAS P WHEELER

Secrelary tor Resoorces

~ 0/ eor-vatJOI\ eDWARD G HElDlG",,,,~

JAMES F DAVISSlate Geologist

CALIFORNIA GEOLOGY stall

In This Issue IUNDERWATER MINING CONFERENCE 122MINES AND GEOLOGY OF FORT IRWIN 123TAMARACK TUFF 130HELP YOUR STUDENTS GET EXCITED ABOUT EARTH SCIENCE 138DMG RELEASES 139

SP 107 MINERAL COMMODITY REPORT-BENTONITE 139OFR 91-07 PRINCIPAL FACTS AND SOURCES FOR

1528 LAND GRAVITY STATIONS ON SAN FRANCISCO QUAD 140INLAND GEOLOGICAL SOCIETY CAll FOR PAPERS 140BOOK REVIEWS . 141MAil ORDER FORM................................................. . 141CALIFORNIA GEOLOGY SUBSCRIPTION FORM.. . 142MEMORIAL, JOSEPH F. POLAND: 1908-1991 . 144

PmIed D8partmef\1 ot General~Office 01 Stall PnnUng

Techrvcal Editor:Asslstant Ed,IOf:GraphICS and DeSIgnPubhcatlQf1s Supervl$Of

Oon DupmsLena Tabilio

Louise HuckabyJelt Tamben

Cover Photo: Paleozoic metamorphic rocks, northeasternAvawatz Mountains. The Avawatz Mountains have beenuplifted thousands of feet since the Miocene. The geologistis standing on an upthrown block 01 Paleozoic meta­sedimentary rock.

0Msl0n H6a<lQuarI8J5. '.'6 Ndl'Ih StrlHl1 Room 1~'

SacranwJ/IIO. CA 9581.(TelellI\O<le 916-445·1~)

P...tlliellOO1lll an<llnlotmalJOn OtlQ'560 Be<QIl Dnve. 5acramenlo. CA 9Sol!1 • .o131PubIoc ltIlOlmalJOn 916-44,s,S716 Underwater Mining Conference

Correction: The third sentence inthe first paragraph on page 68 of theMarch issue should read as follows.The oxygen liberated in photosynthesisis derived Irom water. however theoxygen incorporated into living plantsis derived from carbon dioxide.

los AngMI QIla 107 .$ouOl6t<lOldway. Room 1065t.o. ......... CAIlOO12....c)2IT.....- 21J.620..35(0)

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CAlIFORNIA GEOlOOY (lSSN 0026 4555) III~rnonINybr'1I'MI~oI~,Dmsoonol """"_ GIoIoOY Thtt RacotOI 0lllcI III 1I1 InH'Ol1l SIrgeI.

s.a-. CA 958H s-td d8SS poslIog8 IS paid IIIsaa-,CA~ 5enclllCldresacnanoeslO CALI­FORNIAGEOLOOYIUSPS350a.Qj 8o.2lI8O. Sacramento.CA 958122980

Reports c:oncemng 0MII0n 01 M,,-.-.cl G.oIcoY ~Df6d5

and aroc:lft and .- ~em. ' ....reo to IIle Nrth """""" inCI/Ilor,.. ... lftCluOecl,n II>e 1I'I8IQlU..... Contobuled artdel.~. _ ,1_. ard geoloQIcal meer.rog aI'WIOUIIC8'-

-~-nlE CONCLUSIONS AND OPINIONS EXPRESSED IN

ARTICLES ARE SOlELY TliOSe OF THE AUTHOAS AHD~RE NOr NECESS"RILY ENDORSED BY THE DEP"RT"lENr OF CONSERV"TION

Co,,~ IIIIO\IIll be .,;"r_ 10 Eo*lor, CAUFOANI~GEOLOGY,6608eraIIDrMt.SIo'_.CAIil5ll1.

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June 1991Nolume 44/Number 6

CGEOA44 (6) 12H44 (1991)

The 2200 International Underwa­ter Mining Conference will be heldfrom September 29·October 2. 1991in Kahuku. Hawaii. This forum forocean mining and related researchwill highlight recent developmentsand future projects along the PacificRim. Innovative computer applica­tions in marine minerals explorationand a new underwater drilling systemwill be displayed. Speakers willdiscuss CObalHich crusts of centralPacific seamounts. sea floor chromitesands offshore Oregon. and oUshoremineral deposits along the Alaska

coastline. This forum is sponsored bythe University of Wisconsin SeaGrant InstitUle in cooperation withthe Ocean Basins Division of theMarine Minerals Technology Center.the Continental Shelf Division of theMarine Minerals Technology Center.and the International Mining Society.For further information contact:

Allen H. MillerUnderwater Mining InstituteI BOO University Ave.Madison. WI 53705-4094(60B) 262-0645 x

6 CO2 ,, 12 HzO • C(,HIP(, ..6Hp .. 602

'22 CALIFORNIA GEOLOGY JUNE 1991

Mines and Geology of Fort IrwinSan Bernardino County. Califomia

By

JOHN S. AAPP. Geologist

and

LARRY M. VREDENBURGH, Geologist

) ( IbexPass Kinl!SIOn~Range/"-r:::.. r y...

Fort Irwin

INTRODUCTION

T he examination of mines and miningprospects at Fort Irwin was done

concurrently with Division of MlI~ andGeology (DMG) regklnal geologicmapping and other mineral resourcestudies in the region, Mapping. fieldchecking. and geoIogk data of the FanIrwin region VJere collected betweenJanuary 1982 and May 1990. DMGcondoctcd an investigation of themineral resource potenlial of the FortIrwin regk>n to develop geologic andmineral information in a region ofCalifornia where very little publishedmineral resource informatlon exists. Thisarticle was adapted from an unpublishedDMG Special Report that will be entitledThe mineral resource potential.geology. and abandoned mines 0/Fort Irwin. Son Bernardino County.California.

Trona

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\MILES

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15

Daggett

C:ldyMlns.

'-o-r--40

15

Baker

Kelso

Figure I. Localion map of the Fort Irwin region.

LOCATION AND ACCESS

~., /,•

CAUFORNIA GEOLOGY

, ¥--

..

JUNE 1991

Fon hwin is located in the centralMojave Desen. approximately 40 milesnonh of Barstow (Figure I). The FortIrwin National Training Center employsapproximately 5.800 civilian workers (in­house U.s. Government documents.1987). Part of the southern boundary ofDeath Valley National Monument isfewer than 3 miles north of the Fort. andthe National Aeronautic and SpaceAdministration"s (NASA) Goldstonesatellite tracking facility is located justwest of Fon Irwin.

Photo 1. M-60 tank heading east fromBlcyde Lake. Photos by authors.

Fort Irwin is an important militarytraining center that serves each branchof the anned services. Tens of thousandsof American soldiers recently sent toSaudi Arabia received much of theirdesert warfare training at Fort Irwin.Civilian access is not pennitled duringtraining exercises. The main entrance ofFort Irwin. and the only authorized entrypoint. is on Fort Irwin Road.

DESERT LAND USE DECISIONS

The Mojave Desert is a vast regionwith substantial mineral. energy. andagricultural resource potential. Thou­sands of Californians live. work. andvacation in the desert.

One of the most important desertland proposals pending before Congressinvolves the expansion of the Fort IrwinNational Training Center (Fort Irwin) by370,000 acres of Federal (public), State,and private land. Fort Irwin now covers636.457 acres. and is one of the mostactive military training centers in theUnited States.

Photo 2. Salt Basin prospect. The Salt Basin playa deposits are truncated and displaced bysilvers of the Death Valley taul1 zone. These disrupted beds are underlain by basal conglom­erate and breccia. and overlain by Plio-Pleistocene fanglomerate'. The brown clay-rich saltbeds contain layers of salt and gypsum, and nodules of celestite.

The Department of Defense wouldlike to conduct larger and more compre­hensive military field exercises at FortIrwin. Military planners believe that a

"U .:,' '. ". ~

larger training area is required. Someenvironmental groups. miners. andothers question the need for additionalmilitary land in the desert.

The National Park Service (NPS)proposed that Death Valley NationalMonument be expanded to include theOwls Head Mountains. the QuailMountains. the northern AvawatzMountains. and the southern part of theAmargosa River Valley. The expansionwould make the Monument conliguouswith the northern boundary of FortIrwin. The Monument expansion plan isdesigned to protect scenic and wildlifevalues of the southern Death Valleyregion.

This proposal however. is opposedby the mining community and variousoutdoor recreation groups. Manyexploration geologists believe that theFort Irwin region has good mineralresource potential. There are severaldozen old mines and prospects withinFort Irwin. and hundreds of minerallocation notices have been filed in theoutlying region. Many of the newlocation notices have been filed in theproposed Fort expansion area.

Photo 3. Cave Spring. nonhern Avawatz Mountains. Cave Spring is located adJacenlto CaveSpring Road, just nonh 0' the Avawatz Pass summit. It was a well known geographic featureand watering hole from 1880 to 1920. In 189\ the outpost at Cave Spring consisted of astone corral and a ruined hut. By 1991 all that remained at the Spring were rudimentaryfoundations and "tunnel dwellings." Ephemeral springs issue from weathered andesite lIowsthat have been broken and displaced by movement along the Garlock 'ault zone. 'Bolded terms are in Glossary on page 129.

,,. CALIFORNIA GEOLOGY JUNE 1991

Photo 4. Mining camp ruins, south 01 Avawa1z Pass. A few stone ruins still exist within FortIrwin, although many 01 these turn-ol-the-century mining structures were disman!led anddestroyed by military and civilian visitors several decades ago. These ruins are not idenliliedor documented in the literature. The Army has diligently altempted to pr01ect archeologicalsiles since 1980, especially well·documented American Indian sites like Bitler Spring.

GEOMORPHOLOGY

The terrain of Fort Irwin is mostlybarren and rocky, with rugged moun­tains that are separated by dry lakebedsand broad alluvial fans. A variety ofcacti. desert shrubs. and grasses grow inthe region and are abundant near thefew isolated springs. Alluvial terracesand bajadas sustain sparse perennialvegetation, and the broad playas arecompletely barren.

Pale brown dune sand collects on theleeward sides of sharp ridges andravines. Strong desert winds winnowpoorly sorted fanglomerate terraces.leaving a mosaic of angular reddish­brown clasts called "desert pavement."Although it is called desert pavement.these iron-stained clasts are generallyineffective in supporting off-roadvehicles because they often concealdeep. unconsolidated. wind-blown sand.

HISTORY

The mountain passes and valleys ofFort IrvJin were well traveled by earlyCalifornians. The Old Spanish Trail.which was a lucrative trade routebetween Santa Fe and Los Angeles.passed through the southeastern part of

Fort Irwin. It passed through Red Pass,skirted just north of Bitter Spring. andturned south through Spanish Canyon atAlvord Mountain. Mexican-Americantrade continued from 1829 to 1848.John C. Fremont and Kit Carson werethe most famous early Americans to usethe Old Spanish Trail. In April 1844.while traveling northward on the Trail.Fremonl and his men had a bloodyencounter with Indians at Bitter Spring.Bitter Spring was one of the mostimportant Indian rest and watering spots.

Mormon immigrants discovered placergold near the Salt Springs Hills inDecember of 1849. just east of theAmargosa River, where the riverchanges course to the west. Earlyprospectors traced placer gold from theSalt Springs Hills to its source. theAmargosa lode gold deposit. TheAmargosa mine, which produced aboul$300.000 in gold (Nolan. 1936. p. 52).was worked intermittently from the mid­1800s to 1902. During the 1860s. aroute was established from the town ofVisalia, across the Sierra Nevada throughWalker Pass. the northern part of FortIrwin by way of Leach Lake. then to theAmargosa mine.

' ..,

"-., ~ ~..Photo 5. Much 01 the tuffaceous country rock in the Fort Irwin region is weathered, bleached.and friable. Rock eKposures near Goldstone and the northern Avawatz Mountains exhibitstructural and lithologic features of a volcanic center. A sample of altered meta'volcanic rockIrom the Old Shadey mine. which is located near Cave Spring. assayed 3.06 ounces of silverand traces of gold. The sample also contained high concentrations of arsenic. copper,molybdenum. lead, antimony. and zinc.

CALIFORNIA GEOLOGY JUNE 1991 '"

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':".,

•< •

Photo 6. New Deal mine located in the Owls Head Mountains.appro~imalely 2 miles north of Fort Irwin. Also known as the OwlsHote mine and the Owls Head mine. it was originally developed asan open-pit mine in 1914. One report estimates thai about 4,000Ions 01 manganese ore was produced althe New Deal mine from19161hrough 1956. Trask (1950) reports 480 Ions. The oreaveraged 191043 percent manganese and contained muchhematite.

Cave Spring was an important way station for boraxwagons from 1882 through 1887. The first shipment throughAvawatz Pass came from the short-lived Eagle Borax Works.which was located 21\ Bennett's Well in Death Valley. Boraxwas hauled from Death Valley through Avawatz Pass. to theSante Fe Railroad siding at Daggett (PahaT. 1973. p. 9). Afraudulent mining claim was filed by a desert entrepreneur atCave Spring when the borax wagons began rolling. Teamsterswere charged 25 cents per man and animal for each night ofrest and water. The spring was abandoned when borax miningshifted from the Death Valley region to Calico. and travelthrough Avawatz Pass diminished.

Mineral prospectors came to the Fort Irwin region lookingfor gold and silver in the mid-laOOs. It is very likely that thegold mines of Red Pass. the Avawatz Mountains. and theGranite Mountains were discovered during this period. TheDesert Cave mining district was established by 1880. and thefirst mining claims were recorded within the Fort as early as1872 (Quinn. 1981. p. 19). Silver was discovered in the

Avawatz Mountains in 1872, and Frank Denning discoveredgold at Denning Spring in 1884 (Mining and Scientific Press.1884. p. 262). Gold was discovered in the Paradise Range andat Goldstone in the 18805. Silver mines in the AvawatzMountains and Soda Mountains were recording production inthe late 1880s. and gold was discovered near Quail Springbefore the tum of the century.

Several small mining camps sprang up in and near FortIrwin. Crackerjack was the original camp of the Avawatz Passarea. and one of the few that lasted more than a few months.A post office was established in February. 1907. and a weeklynewspaper, Crackerjack News. appeared a few months later.Regular automobile stage seTVice connected Crackerjack withSilver Lake for a one-way fare of $15.00.

Avawatl City was located 1.5 miles east of Crackerjack. and2.5 miles Irom Cave Springs. According to Van Dyke (1977).Avawatz City originated when eight men from Crackerjack rana Chinese camp cook oul 01 town with the legal authority 01

Photo 7. FaUlt-controlled vein at the Tungate mine. The Tungatequanz vem is discontinuous and relatively free of accessoryminerals, including sulfides. The high-angle Tungate fault IS roughlyparallel to the nearby Garlock fault lone. Later nonheasHrendinglaulls distoned the mineralized Tungate fault. No gold was obseNedin hand specimens. but channel-cut samples of vein quanz assayedfrom O.OOg to 0.08 ounces of gold per ton, plus traces of silver.

'26 CALIFORNIA GEOLOGY JUNE 1991

Undiscovered low-grade epithermalgold/silver deposits may be concealedunder broad eXJX>sures of Tertiaryvolcanic rocks in the region. Miocenezeolite. clay. and saline deJX>sits areamong the youngest and most valuableundeveloped mineral deposits of theregion.

VOLCANOGENIC GOLD DEPOSITS

Tertiary. volcanogenic. gold andsilver-bearing veins occur in severalplaces along the northern border of FortIrwin. Epithermal deposits may bepresent in the G:>ldstone region west ofthe Fort. but there is little supportingdocumentation. Emplacement ofmineralized epithermal veins dependson three fundamental factors: a suitablevolcanic source. receptive host rocks.and an effective subsurface hydro­thermal system. Fort Irwin. and itssurrounding area. appear to have allthree characteristics.

Most of the old workings and historicreferences of the Fort Irwin region relateto Mesozoic calc-silicate skarn andauriferous quartz vein deposits. Skarns

Photo 9. Midway Green quarry is located about 3 miles nonh 01 Dunn Siding. The quarry iscurrently operated by Calico Rock Milling Company. MetamorphiC bedrock is drilled. blasted.and transported by truck to the company plant in Barstow where it is crushed. screened, andsokl as decorative rock.

•

Photo 8. Tiefon Mountam quarry. This aggregate quarry is located on the north slope 01 theTiefon Mountains, J miles east 01 Bicycle Lake. It was developed by an independentcontractor in about 1980, and produced aggregate base materials and concrete aggregatelor numerous Army road and utility construction prOJects. The mine was idie in 1990.

CURRENT MINING

of the region vary in mineral composi­tion and may contain tungsten are(scheelite). gold. iron ore, manganeseare. and calc-silicate minerals (wollasto­nite) that are used in ceramics andcomposites. Various accessory mineralsalso occur.

an unwritten District ordinance prohibit­ing the permanent residence of personsof Chinese descent. San BernardinoCounty authorities worked out a planthat permitted the cook to return toCrackerjack. but division among localresidents over the issue resulted in thecreation of a new town. Dry Camp. DryCamp later became Avawatz City (VanDyke. 1977. p. 25-26).

Other than aggregate borrow pits.mining has not been permitted withinFort Irwin since about 1941. However.mines and quarries dot the countrysideof the surrounding area. Most historicactivity in the area involved preciousmetal mining. Today. industrial mineralsand construction materials are theprincipal commodities being mined inthe region.

MINERAL RESOURCE POTENTIAL

The Fort Irwin region has undevel­oped mineral resource potential.Precambrian talc deposits and gold­bearing quartz veins in the AvawatzMountains are among the geologicallyoldest mineral deposits of the region.

CALIFORNIA GEOLOGY JUNE 1991

-.. -...,

Photo 10. Red Pass Lake. southeast Fon Irwin. Red Pass lake appears to have occupied alarge area west and southwest of the Red Pass Range during the Pleistocene Epoch.Regional uplift has lilted the Ter1iary section 01 Red Pass Lake to the west. thus confining theHolocene lakebed (usually dry) to its western limit against volcanic hills within Fon Irwin.

Small. mostly concealed. iron are andcalc-silicate skarn deposits exist through­out the Fort Irwin region. The mostlikely place to discover new iron ormanganese skarn deposits of e.:onomicimportance is the eastern and northernAvawatz Mountains where massiveplutons of quartz monzonite come intocontact with pre-Mesozoic carbonateroof pendants. Undiscovered iron areand manganese deposits may exist. butregional gravity and magnetic datasuggest that no major deposits lie hiddenbeneath the surface.

MESOZOIC SKARN DEPOSITS

The most favorable areas forepithermal gold/silver deposits are in thenorthern Avawatz Mountains, the areaimmediately east of Goldstone SpaceTracking Facility. the region northwestof Calico and the Red Pass Range. Eachof these areas has broad expanses ofTertiary volcanic and sedimentary rocks.

A relatively small iron and manganeseore deposit could be hidden somewherein the region because Mojave Desertiron and manganese skarn deposits tendto be small. Although small. these skarndeposits are large enough to supply ironare to the portland cement industry ofsouthern California. Brightly coloredrock from these skarns can also bemarketed for decorative rock andspecialty uses.

GOLD-BEARING OUARTZ

Cretaceous poly·metallic. sulfide­bearing. quartz veins occur throughoutthe Fort Irwin region. Auriferous quartzveins have been mined within Fort Irwin.and similar well-documented goldoccurrences have been mined in thearea surrounding the Fort.

Mineralized veins intrude. and appearto be derived from. Mesozoic quartzmonzonite plutons that intrude meta­morphic roof pendants. Most of themineralized roof pendants appear to bePaleozoic meta-carbonate rocks.quartzite, siliceous meta-volcanic rocks,and quartz-mica schist.

Undiscovered Mesozoic poly·metallic.sulfide·bearing. quartz veins undoubtedlyexist in the northern Avawatz Moun-

tains. Granite Mountains. Quail Moun­tains. Paradise Range. and the AlvordMountains. Only those mineral veinsthat have been exposed by tectonic upliftand erosion have been OhselVed.prospected. and developed. Most of theexisting mines were discovered morethan 80 years ago because of gossanexposures. Unless concealed veindeposits have imposed an obviousgeochemical signature to overlying rocksand colluvium. they are likely to remainhidden for the foreseeable future.

The volume and economic value ofundiscovered mineralized vein depositsin the Fort Irwin region are difficult toestimate because of the scarcity ofdetailed geologic mapping and relevantmineral information. It is especiallydifficult to predict the occurrence andgrade of auriferous quartz veins.However. if known mineral occurrencesare representative of undiscovered andhidden quartz veins. the volume andeconomic value of these undiscoveredmineralized quartz veins must berelatively small.

Based on limited assay data andmineral production statistics. it is

assumed that ore grades. depending onthe mining methods. might range from0.10 to 1.0 troy ounces of gold per ton.Also based on limited field data. it isassumed that vein widths would rangefrom a few inches wide to a few yardswide. Veins could range from a fewyards to half-mile or more in length.There may be fault-brecciated zones withcomplex veins and more broadlymineralized areas. It is reasonable toassume that undiscovered mineralizedveins of the Fort Irwin region couldproduce 100.000 ounces of gold.

CONSTRUCTION MATERIALS

The crushed stone mineral resourcepotential of Fort Irwin is limited bypotentially high transportation costs.Until recently. it would have beenunrealistic to consider developing largescale stone quarries in the remOle ForiIrwin region. However. continuoussuburban development of greater LosAngeles has already pushed eastwardinto the western Mojave Desert. It hasbecome extremely difficult to acquireand develop mineral properties west ofthe San Gabriel Mountains. and it maynow be reasonable 10 consider develop­ment of remote desert stone quarries.

'" CALIFORNIA GEOLOGY JUNE 1991

Fort Irwin and the surrounding desertregion has billions of tons of commonSlone that is suitable for dimensionstone. construction aggregate. anddecorallve rock. Rock types that havepotential commeroal value-given aviable market and transportationoptions-include a wide variety ofPaleozoic metamorphic rocks. Mesozoicgranllic rocks. and Cenozoic \dcanicrod"

Non-foliated Paleozoic metamorphicrock types. such as marble. feldspathichornfels. and quartZIte make excellentconslJUcbon aggregate materials.decorauve rock. and dimensk>n Slone.Foliated metamorphic rock often makesattractIVe flagstone. decorative rock anddimenSiOn stone. 1lle best target areasfor Paleozoic melamOr'phic rock depositsinclude the Alvord Mountains. thenorthern and eaSlern Avawatz Moun­tains. Owls Head Mountains. and theSoda Mountains.

Colorful Tertiary vokanic rock fromthe Pickhandle and Jackhammerformations are marketed extensively inthe Barslow regiOn, Similar. colorful.tuffaceous voIcanjc rocks are exposed Inthe Goldstone area. northern AvawatzMountains. near Bitter Spring. and inthe Red Pass area

CONCLUSIONS

II is unlikely that the mineral resourcepotential of the Fort lflA,in regiOn wiD bedeve&oped during the 20th century. FortIrwin plays an important role in mam­laining the natM:lna1 defense. and miningis generally incompatible with IntensIVemililary training. In the 198<h. federalland-use deciSJOOS \A.-'Cl'e heaVily influ·enced by poIJl.icaI aetKln coalitionsconcerned for the enVironment andrecreational assets of the desert region

In the next decade. Important desenland-use decisions WIll be made by theUnited States Congress To assist in this

Glossary

efrort. the Division of Mines andGeology. the U.S. Bureau of Mines. theU.S. Bureau of Land Management. andthe U.S. Geological Survey have invesledmuch time and effort into developing abody of mineral resource and economicinfonnatiOn HopefuUy. this enhancedmineral information will be used byfederal decision-makers in laying oul thefuture of California's Mo;ave Desen

REFERENCES

Nolan. TB., 1936. Melaltiferous resourcesand non-Ierrous metal deposlts _Mtneralresources If1 the reg.on around BouldetDam US GeoIogcaJSurvey.871.P52

Paher, S W , 1973. Death Valley's ghosttowns Las Vegas. Nevada Pub6ca1JOns

QuIM, R.• 1981. An t1Islonc CNefVIf?'N 01 theFoolrwm region, US Army. contract 00.C52010(80). unpublished lI'I-house report

Trask. PD., 1950, Manganese InCa~

CalifOrnia DtvISIOl'l 01 Mmes. BulleIlfl152.

Van Dyke. D.. 1977. Cracker)3Ck-once~a desert. In GL. Moon. editor. lrIe on theMojave RN9r Valley: MOJave River ValleyMuseum AsSOCIatIOn. Barstow. Caillon'llll

bajada: A broad continuous alluvial slope extending from 1M base of mountain ranges intoinland oostns. It forms by the coalescence of a series of alluvial fans.

calc-silicate skarn: Rocks composed largely of cakium'beanng silicate minerals. Calc-silicateskarn minerals are derived from carbonate rocks inlo which large amounts of silica, alumina. iron.and magnesium have been intrcxluced by ootaeent Igneous Intrusions.

colluvium: A general term for loose and incoherent c1aslic deposits. usually depoSited by gravityat the foot of a steep slope. In desert regions. such as Fort Irwin. bajadas form along the lowerslopes of mountain ranges from the uniform coale.cing of alluvial fans and colluvium.

epilhennal deposits: Form within fissures and other rock voids through depositiOn of silica.cakite and other minerals at geologically shallow depths. Ore minerals are brought to the surfaceby means of ascending not water solutions, Geologists divide the family of epithermal aredeposits into a fantastic array of ~ore models.· each with its ()IM'I geochemical and mineralogkalattributes.

fanglomerate: A sedimentary rock made of slightly waterworn heterogeneous fragmentsdeposited in an alluvial fan and later cemented Into a firm rock

gossan: An ok:! mining term that describes a cap of silica and Iron oxide \Ioitich commonlyoverlies sulfide-bearing ore deposits. Sulfide minerals exposed to atmospheric conditions tend toOldditt and liberate sulfuric acid, 1he acid then dis.soNes parts of the host rock and leaves a latticeof ackl·resi.stent silica and iron oxides

playa: A dry. lJl!geIatiOn-free. flat area at the bNest: part of an undrall'led desert basil'll'

CAUfORNlA GEOLOOY .A.lNE 199\ '"

TAMARACK TUFFA Devonian Submarine Pyroclastic Flow Deposit

In The Northern Sierra NevadaPlumas and Sierra Counties

By

JUNE l. LEGLER, GeologistSan Jose State University

ELWOOD A. BROOKS, GeologistCalifornia Siale University. Hayward

and

JOHN S. lULL, GeologistU.S. Geological Survey, Menlo Park

20,

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50

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Miles

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Placerville

Downieville

The Paleozoic island arc and overly­Ing deposits were accreted to the NorthAmerican continent during the Late Ju­rassic Nevadan orogeny (Hannah andVerosub. 1980: Schweickert. 1981),

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Marysville

·Oroville

Figure 1. General location map althe Sierra Bunes-lakes Basin area,Sierra and Plumas coun\l&S,

Chico

99

1892; Tumer. 1895). The Sierra ButtesFonnation and other units in the Paleo­zoic section have been identified geo­chemically as the remnants of a volcanicisland arc (Brooks and Coles. 1980).

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The Paleozoic section in the SierraBultes-Lakes Basin area includes a strati­graphic unit formally designated the Si­erra Buttes Fonnalion (McMath. 1966;Hanson and Schweickert. 1986). TheseUpper Devonian (Anderson and others.1974) rocks are mostly silicic to interme­diate volcanic deposits, interbedded withphosphatic black chert or siliceous argil­lite and intruded by dikes and sills. Themore silicic volcanic rocks are noted forabundant, large (to 1/2 inch) quartz phe­nocrysts and an absence of mafic phe­nocrysts, These quartz-bearing rockswere called "quartz porphyry~ in earlydescriptions of Sierran geology (Diller.

GEOLOGIC SETTING

INTRODUCTION

T he Sierra Nevada. dominantly com­posed of Mesozoic plutonic rocks.

also contains a variety of metamor­phosed volcanic and sedimentary rocksinla which the plutons were intruded.Pre-intrusive rocks largely have beeneroded in Ihe central and southern Si­erra. leaving only scattered remnants.referred to as roof pendants andscreens. The northern part of the rangecontains more of the older rocks andsome of the best exposures are foundjust west of Yuba Pass and north ofHighway 49 in Plumas and Sierra coun­lies. The popular Sierra Buttes-LakesBasin area. located within the Gold Lakeand Sierra City 7.5-minute quadrangles(figure 1). is underlain almost entirely byPaleozoic volcanic and marine sedimen­tary rocks.

Botded terms are In Glossary on page 137.

,,. CALIFORNIA GEOlOGY JUNE 1991

The freshly broken rock is light 10 darkgreen and aphanitic so that few features arediscernible even with a hand lens. Weatheredsurfaces reveal the blocks and coarse lapilli

Outcrop Appearance of the Tamarack Tuff

FIELD OBSERVATIONS

This tectonic event produced a northwest-strik­ing. east-dipping orientation altha strata. Therocks aTe thoroughly recrystallized and mela­morphosed 10 low grade. and locally arestrongly foliated. Nevertheless. primary texturalfeatures of the rocks are preserved well enoughin most places 10 provide the data for the inter­pretations which follow.

Tamarack Tuff

A significant portion of the Sierra ButtesFonnation in the Sierra Buttes-lakes Basinarea consists 01 a particularly distinctive meta­andesitic layer. which we refer to informally asthe Tamarack tuff (Legler. 1983: Legler andBrooks. 1983: Brooks and Legler. 1989).named for the two small lakes near the south­ern outcrops (Figure 2). Because of its relativeresistance to erosion. the Tamarack tuff is wellexposed for about 11 km (7 mLl along strike(Figure 2). forming prominent ridges or thesteep walls of glacial valleys. Unlike most of theother volcanic rocks in the Sierra Buttes For­mation. the Tamarack tuff lacks the character­istic large quartz phenocrysts. Fresh rock sur­faces are greenish. reflecting the presence ofmetamorphic minerals such as chlorite and epi­dote, and are unexceptional in appearance.However. the weathered surface of the tuff isspectacular: a work of abstract geologic art inwhich the vivid rusty-red matrix forms a back­ground that is mottled by irregular whitishpumice fragments of various sizes and bizarreshapes (Photos 1 and 2).

Although the Tamarack tuff can be identifiedas a volcanic rock by its relict texture, the ap­pearance 01 the weathered tuff is unlike that ofother volcanic rocks in the Sierra Buttes For­mation. Our analysis reveals thai these peculiarrocks are a pyroclastic now deposil prooucedby an explosive submarine eruption.

Figure 2. Outcrop map of the Tamarack luI!between Sardine Lakes and lakes BaSin. Sierra.and Plumas counties. Dashed line is the approxi­mate limit 01 the Sierra Buttes Formation. Tips ofarrows indicate sites shown in photos. Triangleshows the proposed vent sileo Base map comPIledfrom portions 01 Gold lake and Sierra City 7.5­minute quadrangle topographic maps.

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CALIFORNIA GEOlOGY JUNE 1991 '"

Photo I. Outcrop surface 0' Tamarack tuN at Tamarack lakes exposures. lightlycolored clasts display a vanety 01 shapes and sizes and are aligned in long dimenSion.The deposit appears bimodal (large clasts 10 liner-gramed matrix) and lacks multiplelayering. The map case in the lower nght is 12mches wtde. Photos by authors.

(collectively referred to as ~clasls" fromthis point on) set in a matrix of fine lap­illl and ash. The clasts. determined fromthin-section analysis to be pumice.weather to light gray-green. cream. orgray-white'smooth surfaces. In contrast.the weathered rusty·red matrix ismouled with dark red. shallow. irregularpits and pale-rimmed. angular raisedpatches.

Shapes and TexturalCharactenstlCS01 Fragments

The pumiceclasts have oddshapes. includingovoid. lensoid.spindle-shaped.amoeboid. ribbon­like. and irregularsinuous forms.Most clasts haveragged outlineswith numerousinflections andwispy terminations(Photos 1 and 2).Less frequently.and unrelated ei­ther 10 size orshape. clasts havesharply-definedperimeters.

The pumiceousnature 01 theclasts is not appar­ent in outcrop.because the visibletextural features are not characteristic ofpumice. Most clasts are uniformly apha­nilic and chert-like due to post-deposi·tional silicification. Clasts are more resis­tant than the matrix and stand out inrelief on outcrop surfaces. rather thanweathering to cavities. as expected forpumice. Many clasts bear lineations (dueeither to flow lamination or to collapseunder compression) which appear in thefield to be fine stratification rather thanpumiceous texture. Some clasts havehollow cores with a few ghost-like.spherical vesicles up to 2 mm in diam­eter. All vesicles are filled with quartzand/or chlorite. but those that are largeenough to identify with a hand lens are100 sparse to indicate pumiceous tex­ture. The vesicuJarity of these rocks ismostly visible on the microscopic scale.

Some "clasts~ are actually roundedxenoliths of quartz porphyry or angularfragments of chert thai underlie theTamarack tuff. The weathered appear­ance of these siliceous xenoliths is simi­lar to true clasts but usually the xenolithshave discrete edges and are morerounded. Although in some cases. theedge 01 the xenolithic core cannot bereadily discerned against matrix

(Photo 2). making it difficult to recognizethe fragment as foreign.

Xenoliths are usually less than 10cm (5 in.) in average diameter and gen­erally decrease in size and abundanceupward through the lowermost 10meters (33 feel) of tuff. Xenoliths arerare higher in the unit. In places. xeno­liths occur only in the basal few inches.The resulting mixed zone identifies theapproximate base of the unit when thecontact itself is unexposed.

Shapes of smaller lapilli in the matrix(Photo 2linclude a variety of subequanlpolygons. triangles. ovoids. and ribbon­like forms. Rarely. the larger matrix frag­ments have sinuous shapes like those ofsome clasts. Ragged edges similar to

those on clasts are common on matrixlapilli. Those ash-sized matrix particleswhich are visible without a microscopehave subequant blocky and ovoid shapes.Overall. the appearance of the matrix isreminiscent of shredded paper clippingsand confetti.

The texture of matrix particles is lessuniform than that of clasts. Lighter col­ored areas of matrix fragments look simi­

lar to clasts. beingsmooth and chert­like, but the dark.reddish patches ofthe matrix have arough. granularappearance. com­pletely unlike clastsurfaces. linea­tions are visible inlarger grains. andsome contain ap­parent vesicles.filled with chloriteor quartz.

Distribution andThickness

Based on ge0­

graphic distribu­tion. internal fea·tures. and chemi­cal composition.the exposures ofTamarack tuff be­tween SierraButtes and LakesBasin are thoughtto represent a

single depositional unit. Most gaps inoutcrop can be attributed to Pleistoceneglacial erosion or cover. However. a 4Ion (2 1/2 mi.) hiatus exists west of Up­per Salmon and wid Lakes (Rgure 2).where the projected stratigraphic posi­lion of the tuff is occupied moslly byheterolithologic tuff-breccia and tur­bidites. The luff-breccia contains largeblocks of Tamarack tuff and probablyrecords erosion of Ihe original deposit bylater submarine debris f1oVlS. Therelore.we think the original distribution of thetuff was continuous for the entire 11 Jon(7 mi.) of present exposure.

The thickness of the Tamarack tul{has been estimated from the outcropmap because no section could be mea­sured in the field. The outcrop at Tama-

'" CAUFQANIA GEOlOGY JUNE 1991

Except for two places, the Tamaracktuff is a single, thick bed. At TamarackLake. for about 40 meters (130 feet) oflateral extenl, lhe tuff deposit consists ofa 75-meter (240-feet) thick inversely-­graded bed overlain by a second 2-meter(7-feet) thick inversely-graded layer. Else­where at the Tamarack Lake outcrop,the bed is overlain along 50 meters (165feet) of its upper contact by a fine­grained. clast-free layer averaging 25 cm(10 in.) thick. This thin fine-grained layerappears to be recrystallized vitric ash

The averagesize. varialion insize, and concentra­tion of clasts de­crease along strikefrom south tonorth. The matrixfragments also de­crease in grain sizeand become bettersorted from south

to north. The matrix appears 10 be sortedcompositionally; the ratio of pumicegrains to vilric granules increases in thematrix from south to north and upwardin the deposit. The matrix at the north­ernmost outcrop consists almost entirelyof bits of pumice.

The whitish pumice clasts are foundthroughout the section in varying abun­dance. making up from a few percent to80 percent of the rock by volume. Over-

all. concentrationof clasts approxi·mates 20 percent.Pumice clasts areinversely graded.and increase innumber upward(Photo 3). exceptat the northern­most exposures.where clasts areevenly distributed.Xenoliths. con­versely. are nor­mally graded andfound mostly nearthe base of thedeposit.

blocks are found in the southern out­crops. The distribution of sizes in clastsindicates the tuff is polymodal. ratherthan bimodal.

Size Dlstnbutlon, Slratlticatlon, andAlignment 01 Clasts

The tuff appears superficially to bebimodal. We attempted to confinn thegrain-size distribution by detennining theaverage dimensions of fragments. Be­cause the finest material is recrystallized.individual malrix particles cannot be dis·criminated completely. Those fragmentswhich are visible show that the matrixconsists of all sizes of dust. ash, and lap­illi to 3 cm (I + in.). The pumice clastscan be measured accurately and mostlyrange from 3to 40 cm (1+ to 16 in.) inaverage diameter. A few individual claststo 2 meters (6.6 feet) and zones withabundant large 1>50 cm or 20 in.)

sian or by erosion. were found in thequartz porphyry and felsic lava whichoverlie the tuff.

Even though the tuff is a submarinedeposit. its contact with ad.iacent rocks isnot depositional everywhere. Quartzporphyry apparently was intruded alongthe lower contact in places. Also. it ispossible that some overlying rocks wereintruded after deposition of the tuff andother units. Fragments of tuff. that couldhave been incorporated either by intru-

l

Photo 2. A close·up view of the Tamarack tuff weathered surface. Wispy ends andhazy edges of the clasts With irregular shapes are typical 01 the deposit. Many 01 thecontrasting darker matrix fragments or varIOUs shapes are rlow aligned, The "clast" inthe upper lefl IS a quartz'porphyry xenolith whiCh has a ooncentnc halo of matrixrragments. Photo wlClth IS 10 Inches.

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The lower con-tact. exposed at the north and south endof the Deer Lake outcrop. west of LongLake. and at several places north of andeast of Tamarack Lakes. is sharply de­fined, Underlying rocks include massiveand brecciated quanz porphyry, chert.and pillowed and massive flows ofandesitic lava. Chert and quartz por­phyry xenoliths occur in the tuff near thelower contact. Lava-flow xenoliths werenot found. but the lava and tuff are simi­lar in appearance and lava fragmentsmay have been overlooked.

The upper contact is not so well ex­posed as the l()\l,'er. but is sharp wherevisible east of Tamarack Lake. southwestof Deer Lake. and west of Long Lake.CNerlying rocks include silicic (dacite?)lava. quartz porphyry breccia. otherpyroclastic flow deposits, and chert.

ContactRelationships

rack lakes is more than 100 meters(325 feed thick. The Deer Lake outcrop,3 km (2 mi.) north. has a present thick­ness of at least 150 meters (485 feet).The tuff appears to pinch out 10 km (6mi.) north of Tamarack Lakes, nearLong Lake. Due to compaction and sub­sequent erosion, the present thickness isprobably less than the original thickness.

Features typk:alof the Tamaracktuff are best seenin two areas. TheTamarack Lakeslocality has mag­nificent displays ofclasts and matrixfeatures. upperand lower contactsof the unit. inter­nal stratification.and primary orien­tation of clasts.The Deer Lakearea contains rep­resentative ex­amples of sorting.size ranges andshapes of clasts.and provides avertical sectionthrough thedeposit.

CALIFORNIA GEOLOGY JUNE 1991 '"

Photo 3. Andge formed by the resistant Tamarack lUll. This outcrop shows !lowalignment 01 large clasts and inverse grading. The tree is about 3 meters (10 leet) high.

t,

which mayor may not be related to thetuff. TIle absence of a second layer inother areas is puzzling: it could havebeen removed by erosion. or thesecond layer may have been only locallydeposited.

Alignment of long axes of both clastsand matrix grains. which appears to beprimary orienta-tion. has been pre-served in someareas, Sinuous,elongate. and largeovoid clasts arealigned with thebedding plane atthe TamarackLakes locality(Photos 1 and 3).Alignment of adja­cent matrix frag­ments suggeststhat the clastswere oriented bylaminar now. Sev­eral other outcropsurfaces showalignment of longaxes of matrix par­ticles. which isconsidered theresult of turbulentnow because align­ment is neitherparallel to beddingnor to metamor-phic foliation.

PETROGRAPHIC FEATURES

Petrographic studies were conductedby the senior author on 96 thin sectionscut from 76 samples of tuff. Microscopicstudy of the rocks was critical to deter­mine the abundance of glass. pumice.and the paucity of lithic components inthe Tamarack tuff. In outcrop. pumiceclasts cannot easily be distinguished fromchert fragments or small lava pillowspresent in adjacent breccia deposits. ex­cept where phosphate nodules arepresent in the chert or where chilledmargins are found on the pillows. Other­wise, thin sections are necessary to seethe mosaic of quartz in the chert. thelesser abundance of vesicles. and greaterabundance and size of plagioclasemicrolites. Microlites are found in pil­low lava fragments and are distinguishedfrom pumice clasts.

The rocks have been devitrified andmetamorphosed to prehnite-pumpel­Iyite or low greenschist facies mineralassemblages. The present rock is a veryfine-grained (less than 0.01 mm diam­eter), foliated aggregate of albite, quartz.chlorite. epidote. calcite. sphene. pyrite,and sericlle, prehnite and pumpellyite,and actinolite (in approximate order of

abundancel. PelVasive foliation is presentlocally. Despite recrystallization and ori­entation of metamorphic minerals. relictprimary features are readily discernible.

Pnmary Textures

Originally. the Tamarack tuff waspredominantly glassy and highly vesicu­lar. with little crystallization. Both matrixand clasts generally have less than I per­cent microphenocrysts of quartz, plagio­clase, and magnetite. and less than 1percent of the tuff is made up of lithicfragments.

The conspicuous lightly coloredclasts consist of pumice containing sphe­roidal vesicles less than 0.1 mm in diam­eter (Photo 4). Vesicles make up at least50 percent of the pumice clasts. but thisfigure probably represents the lower limitof vesicularity. Vesicles now are filledwith quartz and/or chlorite and those

smaller than 0,01 mm cannot be identi­fied reliably within the metamorphicfabric.

The matrix originally consisted prima­rily of pumice fragments. grains of non­vesicular glass. and interstitial glassy dust(now chlorite). Pumice. which makes upa few percent to nearly all of the matrix,

is identical to clastpumice. Glassgrains are sagittateor cuneiform splin­ters and angular,equant granules.Cuspate or Y­shaped glassshards. typicallyfound in subaerialvitroclastic de­posits. were seenin only two thinsections. The rarity

, of these classicshapes is probablydue to the lack oflarge vesicleswhose brokenwalls would pro­duce the shards_

Sparse perliticcracks occur bothI.Vithin individualclasts or matrixgrains and con­tinue across grains.

Other devitrification features, includingaxiolitic structures. spherulites. and"snowflake texture," (an intergrowth ofquartz and feldspar which develops indevitrilied collapsed pumice) (Anderson.1969), are present, but rare.

Several kinds of nonmetamorphicdeformatk>n were identified Collapsedpumice occurs in several samples. indi­cated by streakiness in the mosaic and bysnowflake texture. Some pumice vesiclesare flattened parallel to adjacent grainboundaries. Recurved and flattened glassshards and granules molded againstother grains are present in two samplestaken from near the base of the deposit.

Primary Mmerals

Sparsely scattered microcrystals inthe Tamarack tuff consist of whole andbroken euhedral bipyramidal quartzphenocrysts and plagioclase microlites.

'" CALIFORNIA GEOLOGY JUNE 1991

Photo 4. PhotomICrograph. ~ane polanzed light. shoWing the lower limit ot vesicularity(about 50 percent) 01 the pumice fragments. Vesicles average less than 0.1 mm Indiameter. are tilled mostly With quartz with lesser chklflte and are deformed bymetamorphic foliation. The horizontal field 01 view is 2.5 mm (0.1 in.).

Quartz commonly is embayed or frac­tured. Most quartz crystals are less than0.5 mm across but range in size to 2.0mm and are visible in outcrop. Plagio­clase microlites are generally between0.01-0.05 mm in length. but range to1.5 mm. with the notched terminatjonsand hollow centers that are common inquenched crystals. Quartz and plagIo­clase are subequally distributed in therock.

CHEMICALCOMPOSITION

Compositionsof 47 whole-rocksamples. compris­ing 13 matrix andclast pairs (col­lected from thesame outcrop). 14clasts. and sevenmatrix samples.were determinedby x-ray fluores­cence analysis(Legler. 1983:Legler and Brooks.1983; Brooks andLegler. 1989).5iOz ranged from50.5 percent to67.] percent andaveraged 59.8percent in matrixsamples which areconsidered theleast altered. Silicain clasts rangedfrom 65.1 percentto 84.9 percent arK.! averaged 71.8 per­cent. The difference in silica content be­tween clasts and matrix is attributed tosilica infllling of abundant vesicles in theclasts and does not necessarily indicateoriginal differences in rock chemistry.Analytical results indicate an andesiticcomposition for the Tamarack tuff.

DISCUSSION

Origin by Submarine Pyroclastic Flow

The Tamarack tuff displays a numberof characteristics which have been de­scribed for both subaerial and subaque­ous pyroclastic flow deposits eruptedand deposited under various conditions(Ross arK.! Smith. 1961; Francis arK.!HO\WlIs, 1973; Sparks and olhers.1973; Sparks. 1976: Sheridan. 1979;

Rsher and Schmincke, 1984). These in­clude andesitic composition. vitroclastictextures. an abundance of pumice. In­verse grading of pumice blocks. normalgrading of lithic fragments. conformitywith adjacent bedded units. large arealextent. poor sorling. polymodal grain-sizedistribution. and stratification whleh com­prises a single very thick bed with or with­out an overlying. much thinner layer.

Several lir'es of evidence infer thatthe Tamarack tuff originated from asingle explosive eruption in a submarineenvironment. The great variety of shapesof fragments with irregular boundariesand many innection points indicates brec­ciation by explosion. rather than by hy­dro-quenching or other means (Walkerand Croasdale. 1972; Honnorez andKirst. 1976) Also. the sparsity of largermicrolites or microphenocrysts in the tuffand the presence of quench crystals areconsistent with rapid cooling during ex­plosion. These features are evidence thatthe tuff did not develop as a hydrobrec·ciated lava flow. such as the adjacentandesitic isolated-pillow breccia that hasabundant. large microlites.

Combinations of laminar and turbu­lent flow are typical in pyroclastic flows(Sparks. 1976; Fisher. 1983). Clastslocally are aligned by laminar flow atTamarack Lakes. EJsewhere at that out­crop and at Deer Lake outcrop, randomorientations of elongated clasts and flowlineations record the turbulence whichwould be expected by rapid ejection anddeposition of a mass flow of exploded

tephra. The ir­regular lower con­tact at TamarackLakes and the sizeand number ofxenoliths suggestturbulent corrosionof the underlyingquartz porphyry.Turbulence in theflow is the prob­able cause of cha­otle incorporationof chert into thebase of the tuff atLong Lake and isa likely contributorto the geometry ofclasts (see below).Turbulence alsooccurs during sub­aqueous sedimentflows. but the re­sulting depositsusually have fining­upward patternsthat are lacking inthe tuff.

The adjacentpillow lavas and litlle-disrupted chertlenses. which conformably underlie andoverlie the tuff in places. attest to sub­marine deposition of the tuff. Further­more. small size of vesicles in pumiceand near-absence of broken-bubble glassshards. such as in the tuff. are character­istics attributed to suppression of vesicledevelopment urK.!er high hydrostaticpressures (Heiken. 1974).

The absence of multiple layers withinthe deposit suggests that a single epi­sode of eruption and deposition oc­curred. The two-layer sequence found atTamarack Lakes is similar to descrip­tions of other single eruptions, and sub­marine pyroclastic now deposits (Fiskeand Matsuda, 1964; Niem, 1977). Fur­thermore. the lack of turbidite sequences

CALIFORNIA GEOLOOY JUNE 1991

in the tuff implies that the erupted mate­rial moved not as a water-fluidized cur­rent. but as a gas/grain mass flowwncrein the gas pressures excluded sig­nificant invasion and disintegration bywater. The abundance of delicately an­gular and irregular shapes throughoutthe deposit indicates that abrasion wasnot extensive during transJXIrt. nor is itlikely that the material was reworkedafter deposition.

Volume 01 the DePOSit

The volume of the Tamarack tuff iswithin the range for other known pyro­clastic flow deposits (Rsher andSchmincke. 1984). "The thickness nowaverages about 100 meters (328 feetl.which is less than the original. Assumingthat Ihe gap in outcrop west of SalmonLakes is the result of laler disruption. thetuff extended for at least 11 km (7 mi.)in one direction. Present orientation in­hibits assessing the wKlth of the deposit.but the broad Deer Lake outcrop pro­vides a lO\.ver limit of 650 meters (2.130feet) of width. The present exposures.therefore. reveal a minimum of 0.7 kmJ

(0.2 mi.l) of malerial in the deposit.Since many pyroclastic flow deposltshave equldimensional areal extent (Rossand Smith. 1961: Sheridan. 1979). it ismore reasonable to assume tnat tncwidth was equal to the length. in whichcase the volume would approximate 12km J (2.9 mi.3).

Possible Vent Location

Thickness and distribution of tnc de­posit. along with sorting and rounding ofthe fragments. suggest a south-to-northdirection of tranSJXIrt of the Tamaracktuff from a vent site south of TamarackLakes. A plug south and west of Tama­rack Lakes (Figure 2l. consisting of rockssimilar in composition to the tuff and tothe underlying andesitic pillow breccias.is speculated to be the eruptive center.However. talus and glacial debris unfor­tunately mask any confirming field evi­dence.

Origin ot Unusual Clast Geometry

The unusual shapes of c:1asts arethought to result from two factors: greatplasticity of the pumice (indicated byelongation of vesicles and alignment ofplagioclase mlcrolitesl and turbulence

during eruption and transport of theflow. Pumice often has a lower viscosityand greater plasticity than associatednon'vesicular material because 01 thehigh gas concentrations in the pumice(Ross and Smith. 1961). Ross and SmHhstate that viscosity also derives fromcomposition and temperature of theglass. but even slight variations in gascontent can lead to rapid changes in vis­cosity. When pumice collapses underpressure, some of tnc tTapped gasesmay go back into solution. which de­creases viscosity and increases plasticityof the glass.

In a pyroclastic eruption. the blobs ofglass which separate from the eruptingmass would mold and distort during ex'trusion. Deformation could contlnue un­til cooling and loss of gases froze theblob to a rigid. pumiceous glass. [f somere-solution occurred during impacts oftumbling in the turbulent mass, the pe­riod of plastic behavior would be ex­tended. Many of the contorted clastsprobably fom1ed during turbulent extru­sion and shortly thereafter.

Oast shapes suggest that fragmentsin the tuff remained plastic and weremolded additionally during transJXIrl anddeposition. Ratlened vesicles. collapsedpumice. and vesicles deformed againstadjacent fragments could develop onlywhile the glass was plastic and these oc­cur at considerable distances from theinferred vent. Delicate protrusions andfeathery edges are found on fragmentsseveral miles from Ihe Implied vent andprobably did not fOffil only during erup­tion. It seems unlikely these featureswould have suTVived abrasion duringtransport over that distance. These frag­ile features must have fanned duringtransport by tearing of still-plastic blobsor after deposition from compression ofthe plastic mass.

SUMMARY OF FINDINGSAND THEIR SIGNIFICANCE

The Tamarack tuff is a devitrified andrecrystallized andesitic tephra depositwith textural and structural features typi­cal of pyroclastic flow deposits. Petro­graphic and field evidence indicates sub­marine eruption and deposition. Tex­lures. fragment morphology. stratifica­tion, and orientation of componentsshow thaI the tuff was e)e<:ted explo-

sively and moved by turbulent and lami­nar flow for at least 11 km (6.6 mi.).producing a deposit over 100 meters(325 feet) thick. This mass flow appearsto have originated at a vent near what isnow the southern end of the deJXIsit.

Pale. weathered. chert-like clasls.which give the Tamarack tuff its distinc­tive outcrop appearance. are pumiceblocks and Iapilli. Extremely fine vesicu­Iarity. contorted shapes resulting fromplastic deformation during eruption.transport. and deposition. and subse­quent silicification have disgUised the na­lure of the peculiar pumice fragments.

Sparse evidence suggests that weld­ing may have occurred al the base of thedeposit and possibly stratigraphicallyhigher in those portions of the depositnear the vent. Evidence for welding isinconclusive and still under investigation.but includes some petrographic featuresassociated with subaerially depositedwelded tuffs. Weak welding would ac­count for the initial preservation of theTamarack tuff.

Although explosive submarine erup­lions should be common in oceanic vol­canic arcs. few submarine pyroclasticflow deposits have been described. Suchdeposits are often disrupted by currentsor subsequent eruptions soon after depo­sition. Older deposits which survive thisvigorous submarine activity may becomealtered beyond recognition during subse­quent tectonic events or destroyed byerosion. Similar modem deposits can bestudied only by dredge samples and drillcores which give an incomplete pictureof their extent and fabric. "The opportu­nity to study the Tamarack tuff subma­rine pyroclastic flow deposit is as uniqueas its outcrop appearance. The docu­mentation of significant criteria for iden­tifying the tuff may aid in the recognitionof other such ancient deposits.

ACKNOWLEDGMENTS

D. Harwood and S. Silva. both withthe United States Geologic Survey inMenlo Park. reviewed this paper andoffered suggestions for additional investi­gations on the tuff. Reid work was sup­ported by a grant from the GeologicalSociety of America.

'36 CALIFORNIA GEQlOOY JUNE 1991

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Honnorez. J., and Kirst, P., 1976. Subma­nne basaltIC volc¥llsm MorphologICalparameters lor di$CnmmatU'lghyaodasbles trom hyalottJlfs: B.JIefJfJVokanoloQlque. v 39, no. 3. p 441-465

legler. J,l., 1983. A submanne pyroclasticflow depo$lt in the SIerra Buttes Forma·IlOI'l nortl'lefn $len Nevada. C81rforna:M.S. thesis. calilcyl'lla State lJrIIVer$ItV.Hayward. 149 p

legler.J.l.. and Brooks. E A.. 1983. A sub­marine pyrodastIC flow In the Devonl3nSletra Buttes FormalJOn, SIerra andPlumas counttes. California: GeoIog1caISooety of Amenca Abstracts Wrth Pro­grams. v. 15. no 5, p 330

McMath. V E . 1966. Geology of the Taylors·VIlle area. northern SIerra Nevada. CaJt.

Glossary

fOfl1l3. In BaIley. EH . ecitOf. Geology 01northern California: California Division orMInes and Geology ~lIe\ln 190, p. 173­184

N'em. A_A.• 19n, MI$SISSlpp&an pyrodasllCtlow and ash fall depoSits In the deep ma­rine OUachila flysch basin, Oklahoma andMansas GeologIcal Soaety of AmentaBulIellfl. y 88. P 49·61

Ross. C.S.• and Srruth. A.L., 1961, Ash flowtutls: Iheir origin. geologic rela\lons. andidentlficatlOrr U S Geologlc.al SulV1ily Pro­fes5lOf\al Paper 366. 54 p.

SChweICkert. A.A., 1981. TectonIC evolulJOnot the Sleffa Nevada range, In Emst,W G.• editor. The geoteclOnlC evolutIOn ofCa~fornia Pronbco Hall. Incorporated. p87-131

Shendan. M.F.• 1979. Emplacement 01 pyro­ClastIC flows: a review: GeologICal Societyof America Special Paper 180. p 125-136.

SparXs. A_S..!. 1976. Gralt'l SIZe varl3tJOnS 111lQf1lmbnt8$ aoo IffipllcalJOnS for the lJans­port of pyroclastIC flows: Sedimentology, v23. p. 147-188.

Spar\(s. R S.J . Sell. S, and Walker. G.P.L,1973. ProdI)cts ollQf1lmbnt9 erupboflsGeology. v 1,p.115-118

Turner, H.W.• 1895. The age and succesSIOn01 the igneous rocks 01 lhe Sierra Nevada.Calilomta; Journal of Geology. v. 3. P385414.

Walker. G.P.L, and Croasdale. R.• 1972,CharacteristICS 01 some basalticpyroclaslJcs Bulle/In VoIcanrJlofpque.v 35. p. 30)-317.

axiolitic: A rock textll"e in which needle-like crystals radiatefrom a central axis rather than from a point

bimodal: A grdin or fragment :!>lie dbtribuUon having twoSizes ocornng ""ith greatest frequency.

euhedral: A mineral grain completely bounded by its 0'AIl1

regularly deYeloped cl)-stal faces.

felsle: A term applied to igneous rocks contatning abundantlight-colored minerals prtmarily quaru and feldspar.

greenschist facies: Metamorphic minerai assemblagerepresentoo by albite + epidote + chlorite + actinolite andcharaeteri~ticof Iow-grade regk>naJ metamorphism.

heterolithologic: Ctastk: rocks containing fragments ofdifferent rock types.

hydrobrec:ciated: Broken mto fragrTMmls by contact...,;mwateT.

inversely graded: A sedimentary structure In which grainor fragment size increases upv.rards within a bed.

lapllll: Volcanic fragments thai range m size from2 to 64 fTI11.

CAUFORNIA GEOlOGY

mafic: Dark-colored iron and magnesium bearing mineralsor a rock composed primarily of these minerals.

miaoille: MlOute crystals. usually of tabular or pnsmaticmape.prehnite-pumpellyite facies: Similar to greenschist faciesbut containing the minerals prehnlte and pumpeJyite

tephra: A general term for aD fragmenlal volcanic matenalejected during an eruption and transponed through the air.

turbidite: A sedimentary rock deposited from a sediment­laden current and chaBCterized by graded-beddmg.moderate sortlJl9 and loVeD-oo.oeloped layering in a fixedsequence.

vitric: Pyroclastic ITIdterial containing more than75 percer:t qlass partides.

vitroclastle: A pyroclastic rock structure characterized byfragmented bits of glass.

volcanic island arc: A geneTally Q.lIved Unear belt of~)c islands klcatoo above a 5UbdllCbOn zone

xenolith: A foreign Inclusion in an igneous rock.'"

.lJNE 1991

A Page For Teachers

Help Your StudentsGet Excited About Earth Science

Help for planning activities isdifficult 10 find. say many scienceleachers and uoluntcers. This source/IS! was compiled to help you stimulateinterest in your earth science students.

Earth Science Investigations.edited by Margaret A. Ooslenllan andMark T. Schmidt. The AmericanGeological Institute (AGl) published thiscollection of activities for grades 8-12 infall 1990. The 26 activities weredeveloped by teachers. reviewed byscientists and tested with students. Eachhands-on exercise provides the con­cepts. vocabulary. and \VOrksheets. plusan answer key when applicable. Orderfrom AGI. 4220 King Street, Alexan­dria. VA 22302. (703) 379-2480:spiral-bound book. 231 pages. $34.95plus $4 postage;1landling.

Inside Hawaiian Volcanoes. a 25minute color video. illustrates techniquesfor monitoring Hawaiian volcanoes. Thevideo. aimed at audiences of all ages.includes spectacular eruption footage.Subsurface features are depicted bycutaway views. models. and computergraphics. Noted volcano cinematogra­pher Maurice Kraft produced the videoin collaboration with the U.S. GeologicalSurvey and the Smithsonian Institution.Orders must include check or moneyorder made out to Smithsonian Institu­tion. Send to Richard S. Fiske. NaturalHistory Building 119. SmithsonianInstitution, Washington. DC 20560.(202) 357-1384: videotape. VHSformat $20.00. PAL format $25.00.

The teacher's guide for InsideHawaiian Volcanoes containsquestions and lab exercises. Order fromthe U.S. Geological Survey (addressabove): USGS Open Ale Report 89­685. $3.50 for paper copy, $4.00 formicrofiche.

Earth Science Research Activi­ties, by James Scannell. Published in1988, this book is one of four in theseries, Explorations in Science. Itcontains 50 ready·to-use individual andgroup enrichment activities for grades 8­12. Each has been tested and includes ateacher's guide and answer key. Orderfrom Alpha Publishing Company. 1910Hidden Point Road, Annapolis. MD21401, (301) 757-5404: spiral'boundbook. 273 pages, $35 plus $3.50postage/handling.

Resources for Earth ScienceTeachers 1991 lists 43 sources ofearth science reference and enrichmentmaterials including catalogs. publicationslists. teacher packets, books. andjoumals. To get a copy. contact theAmerican Geological Institute (AGI),National Center for Earth ScienceEducation. 4220 King Street. Alexan­dria. VA 22302 (703)379-2480.

Earthquakes: A Teacher'sPackage for K-6, a six-unit book. wasdeveloped by the National ScienceTeachers Association INSTAl with agrant from the Federal EmergencyManagement Agency (FEMA). It is acomplete earthquake curriculumcontaining activities, lesson plans. linemasters. and background information.Order Irom FEMA. Earthquake Pro­gram. Marilyn MacCabe. 500 C Street.SW, Washington. DC 20472: one freecopy to schools (while supplies last).Order additional copies from NSTA(address below): $15 plus $2.50postagelhandling.

Earth: The Water Planet, a bookof readings and activities for middle­grade teachers. resulted from a jointproject of Horizon Research. Inc.. andAGI. Order from NSTA, 1742 Con-

neclicut Avenue. NW. Washington, DC20009. (202) 328-5800: $16.50 plus$2,50 postageihandllng.

How to Construct a Paper ModelShowing the Motion That Occurredon the San Andreas Fault Duringthe Loma Prieta, California,Earthquake of October 17, 1989,is available Irom the U.S. GeologicalSurvey. Books and Open-File ReportsSection. Box 25425. Denver. CA80225. (303) 236-7476: USGS Open­Ale Report 89·640A. $1.50 for papercopy. $4.50 for microfiche.

Oceanography for landlockedClassrooms, for leachers of grades 7­12. contains easy-to-follow lessons andactivities written by marine educatorsfrom high schools and universities.Order from National Association ofBiology Teacners. 11250 Roger BaconDrive #19. Reston. VA 22090. (703)471·1134: $15 plus $2 postage/handling.

Water in Your Hands, an imagina­tive 16-page booklet. uses cartooncharacters to help children (grades 4-6)develop awareness of water quality andmanagement problems. TIle instructor'sguide includes actillity masters. back­ground information. implementationsuggestions, optional activities. andsources of additional information. Orderfrom Soil and Water ConservationSociety, 7515 N.E. Ankeny Road.Ankeny.IA 50021-0764. (515) 289­2331 or (800) THE-SOIL: single copies$2, discounts on bulk orders.

Reprinted with permission fromBlue/ine(v. 24. no. 1. spring 1991).newsletter of Ihe Association of EarthScience Editors.....

'" CALIFORNIA GEOLOGY JUNE 1991

DMG ReleasesSPECIAL PUBLICATION 107

MINERAL COMMODITY REPORT­Bentorllte and Fuller"s Earth By MichaelA Silva and Daniel T E~, 1990,37 p. $5.00

Minerai COffimOOity reports describetile availability and demand for industrialminerals in California. the United Stales.and the world. Part I consists of UnitedStates and worldVJide mineral statisticalInfonnation and analysis adopted directlyfrom the U,S, Bureau of Mines MMineralCommodity Summaries. M Part [[discusses the geology and productionand marketing of industrial minerals inCalifornia

SpedaI Publication 107 describesSignificant occtJl'Tences of benlonLle andtuner's earth in California by county.Bentonite is any clay thaI is composeddominandy of a smectite clay mineralin tum. smectite is a class or group ofclay minerals. formerly caDed the montmorillonlle group. that posses swellingproperties and high catiOn-exchangecapacities, Smectite day mineralsInclude montmorillonite. hectorile.saponite, and nonlronite. FuJler"s earthIs a bentonite that has absorbing,decolorlzing. and purifying properties.

Fuller 5 earth is not produced in Calif01"­

rna at Ihis lune 1he most prodOClivebenlonite deposits ,n Callfomia are inSan Benito. Inyo. and San Bernardinocounties

Benlonlte is used for a variety ofcommercial applications In manyindustries, Sodium bentonite is used inwell drilling operations; it funclions as asealant. conditions the drill hole andholds the drill hole open. and aids inbringing up drill hole cullings. Bentoniteis also used as a impermeable liner forlandfills and waste water ponds. and as abinder for foundry molds and iron arepellets, Calcium bentonite is used as anadsorbent for removing lmpurihes frommineral and vegetable oils. Calciumand sodium bentomtes also absorb petlA"astes (cal litter) and are used forrenlO'JIng grease and oils from floorsand driwv,:ays, Bentonite is heatedand expanded to produce lighlWelghtaggregale that is commonly used inskyscrapers BoIh IypeS are added 10

animal feed for trace element retentionand are used to carry peshcides.

Specially treated bentonite orchemically unique bentonlle is usedfor specialty products Specialty uses

include filtenng agents for beeT andWUlC. ingredienls in cosmetics. medi­cines. pamts. inks and adhesives. andadditions 10 ceramic and tile mixes toincrease flow

In 1988. according to the U.S.Bureau of MUleS. California produced2.200.000 tons of clay worth over$31.000.000. Bentonite productionwas reported at 137.000 Ions VJOrth$10.000.000 (this production accounlsfor 6 percent of clay by volume. yelalmost one-third of the value of the clayproduced in California during 19 ),The majority of bentonite mined wasnon-swelling and is used maInly for pel

adsorbents. oil and grease adsorbents.and animal feed additives, MOSI of theswelling berllonite is used for paint. inks.cosmetics. and other similar high value­added materials

A1lhough bentonite reserves are largeand the Umted States is self-sufhcient inthIS commodity. environmenlal issues.conflicting land use. and competilion forpubhc lands have adversely affecledmining COSIS, 1llese increased costs havemade imported materials. especially fromMexico. more attractive in some marketareas.....

The Newberry tlecIOnl8ITUne operated byRheox. 11'lCOfPOl"8ted(formerly NL Indus·trIeS). Hec1on1e IS acoIlodal. geI.fonnIngtype of bentOl'llle clayused lor pharmaceutl.cals. cosmebCS, anddanficatlOll 01 wneNote the charaeten5tJ·cally Intense while color01 hectonle Pholo byJohn CI",kenbeard

CALlFQflNIA GEOLOOY JUNE 1991 '"

DMG Releases (continued)

OFR 91·07

OFR 91·07 PRINCIPAL FACTS AND SOURCES FOR 1528LAND GRAVITY STATIONS ON TIiE SAN FRANCISCO I BY2 QUADRANGLE. CAUFORNlA. By Rodger Chapman.

Gravity data are frequently used in studies of local and regionalgeology. For example. these data can be used to investigategeologic structures such as subsurface folds. faults. and possiblesources of groundwater or mineral resources. Many multi-purposegeologic studies that include gravity measurements have beenmade in the San Francisco area. These earlier data were used toproduce maps of the area showing contoured gravity values.Additional work has either been done or is Clunmtly underway inthe area. These new data will be combined with the older data tomake new. more detailed maps of the area. OFR 91-07 com­bines and documents the older data to provide investigators withthe information in a convenient form. It is intended that thisreport will enable investigators to readily find the sources of datathey need so that they can ascertain data accuracy and usefulness.

OFR 91-07 has ten tables of gravity data arranged by sources,information on the reduction processes used, the base stationsused. and the sources of the data. Maps showing the location ofmost of the gravity stations are included. Copies of OFR 91-07may be purchased by check or money order for $8.00.

Make check or money order payable to theDivision of Mines and Geology.

GeologiC Informationand Publications Office

660 Bercut DriveSacramento, CA 95814-0131(916) 445-5716(Reference copies. over-the-counter sales.pre-paid mail orders)

San Francisco Bay Regional Office380 Civic Drive. Suite 100Pleasant Hill. CA 94523-1921(4151 646~5920

(Reference copies and over·the-counter sales)

Southern California Regional Office107 South Broadway. Room 1065Los Angeles. CA 90012440212131620-3560{Reference copies only)X'

Inland Geological Society Call for Papers ---..

'"

The Inland Geological Society invitestechnical papers for its newest volumeentitled MQuaternary Faulting andRelated Phenomena in the Inland andDesert Areas of Southern CaliforniaMtobe published in June 1992 Thisgeographically large and varied regionconsists of most of southern Californiawith the exception of the coastal areas.Only high quality. original papers will beconsidered. This publication will besimilar 10 the Society's previous volumeentitled ~Landslides in a Semi·AndEnvironment:' Any topic related tofaulting is encouraged.

CALIFORNIA GEOLOGY

Abstract deadline: December 1. 1991

Manuscript deadline: March I. 1992

For more infonnation. contact:

Gary S. RasmussenIGS Publicatlons Committee Chair1811 Commercenter W.San Bernardino, CA 92408(714) 888-2422'·

JUNE 1991

Book ReviewsBookS reviewed in this section are not available for purchase from OMG.

Astronomy

SPECIAL REPORTSSA73 EconomIC g60logy 01 the Panamlnl Bune quadraogle and Modoc dlStrlCl,

loyo County. Cahtornla 1963 $4.00SR88 Geology or lhe (}..lettn of Sheba lead mme. Death Valley. loyo Couoty.

Ca~1omla 1965. 53 00_SR96 GeoIogoc roconna,ssance of lhe Slale Range. San Bernardloo and 10)'0 counues.

Ca~rorrwa 1968 $4 00SR 119 Landshding In manne tell'ace lerraln. Cahfornla 1915 $3.00SR I 42 Geology and slope slabi~ty 10 se~ed parts or the Geysers geolhermal area

(SooomaCou1lly),CalllOfOla.I980.. $800

F,"

"'00

... 00$3.00$300$300$8005500

$10,00$20 00.. $1.25

.. $4.00

... 00$8.00$8.00

......... $9.00

Pnce H'lClvclespostage and sales tax

figures of mythology and is not due totheir imagined resemblance; instead.areas of the sky .....-ere dedicated in honorof mythical figures and the familiarpictures of these figures were then filtedto the patterns of bright stars more than2000 years ago. The patterns of starswe see today may not necessarily bewhat the andents saw. The designationof constellations to specific areas of thenight sky helps account for the lack ofobvious resemblance between starpatterns and the mythical figures theyrepresent.

SPECIAL PUBLICATIONSSP49 Cahlorr'lJa jade. a c:oIlec1lOO 01 repflots 1976SP57 Proposed earlhquake safety P'oglams and actl ....lles 01 the Departmenl 01

Conservation, fiscal yeals 1982 11l1ough 1986. 1980 ..SP69 An annotaled bibliography 01 geolhe-rmal informatloo published or authored by

$1311 althe Cahforrua Dlvisioo of MII'l8S and Geology. 1984SPBl M'l'l8ral convnodlly repol1 . sodIum sulfale 1985SPB3 M'l'l8ral mmmodiry report • SOdIum carbonate 1985SP84 M,oe.al convnodity feport· phosphale rock. 1985SPB6 Foolhlll counlles rnOlog handbook. 1985SPI07 M,oe/al commodity leport bentOOlle and fUller's eal1h 1991 (NEW),

Universe as it looked more than 12billion years ago. The opportunity to beso easily informed about the immense·ness of the Universe is a tribute to thescience of astronomy.

The constellations. such as the 12familiar constellations of the Zodiac. areimaginary (jgures superimposed on thepatterns of stars we see at nighl. Manyconstellations were invented thousandsof years ago. The invention of theconstellations probably results fromsymbolic representations of prominent

IIIIIII CALIFORNIA GEOLOOYI 1 year 112 ISSUes)

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BULLETINSB114 Pumoce. purT1lClte, and vok;arllc c....ders in Ca~forrlla 1956B191 Umestone. dolorrIIle. and shell resources or the Coast Ranoes provInce 1978.B I98 Urban geology masler plan lor Califorrlla 1973B199 Basic geology oItl1e Santa Margarita area, San LUIS Obospo County. 1976

THE CaESTIAL PLANISPHERE,Poster ollne Universe as it appears inthe Northern and Southern hemi­spheres. Compiled and designed byTomas Filsinger. 1990. Available from:Celestial Arts. P.O. Box 7327. Berke­ley, CA 94707. Posler is 24 inches x 36inches. A 2B·page manual is included.$14.95 (add $2.25 for postage andhandling lor I to 10 posters).

As we gaze at the celestial bodies Inthe night sky. we see into the past. Thenearest stars to Earth other than the Sunare more than four light·years away.Light from the Magellanic Clouds-orgalaxy c1uster-----can be seen with thenaked eye In the Southern Hemisphereand takes 150.000 years to reach Earth.Scientists using the latest technologiescan hear the echo of the big bang andare seeing the far reaches of the

This planisphere pro)ection of theUniverse dUring the year 2000 includesa polar projection from the NorthernHemisphere connected to a polarprojection from the Southern Hemi­sphere. It shows galaxies. galacticdusters. quasars. constellations. plan­etary nebulae, meteor showers. planetsin our solar system (other than Earth),black holes. and stars: pulsars. super­giants. red giants, neutron Slars. whitedwarfs, and supernovas. This poster iscoated with a phosphorescent paint tnatallows the stars. galaxies, and otherrepresented bodies in the cosmos toglow in the dark after being illuminatedby a light source: the Milky Way galaxy,containing 40 billion stars, is a promi­nent feature. The accompanying manualincludes descriptive information on howto understand and interpret the poster.Also included are astronomical tables. abrief histOJY of celestial astronomy, anddefinitions of astronomical terms such aspulsars and nebulae.

CALIFORNIA GEOLOOY JUNE 1991 '"

• • • • • more BooksEnergy Geochemistry

, NEW SUBSCRIPTION: Allow 60 days lor delivery of first issue

CALIFORNIA GEOLOGY SUBSCRIPTIONS

CITY ~ _

ADDRESS ~ _

This book combines much of theknowledge and recent research aboutthe complex geochemistry and mineral­ogy in oxide zones. Oxygen dissolved ingroundwater is a powerful oxidizingagent. particularly when heated. ll\eoxygen/water solution reacts with manycommon minerals to produce strongsolvents. such as carbonic acid. hydro­chloric acid. and sulfuric acid. Overgeologic time. such chemical reactionshave produced significant melallic oxidezones peripherally to the original sulfidedeposits. This book is designed forgeochemists. mineralogists. environmen­tal chemists. and researchers in ground­water or soil contamination by heavymetals. An extensive bibliography isincluded and is listed by topic at the endof each chapter.

Oxide zones form by the weatheringof sulfide minerals near the surface ofthe Earth. Sulfide minerals in turn formfrom silicate melts or by precipitalionfrom geothermal water from silicatemelts. Oxidized mineral zones are animportant source of metallic ores andhave been mined for many centuries.These metallic oxide zones are theprimary source of base metals such ascopper. lead, and zinc. Other importantmetallic ore deposits in these zonesinclude !In. iron. and tungsten. Most ofthe spectacular museum specimenscome from these oxide zones.

OXIDE ZONE GEOCHEMISTRY.By Peter A. Williams. 1990. Availablefrom: Prentice Hall. Prentice HallBuilding. Englewood Cliffs. NJ 07632.286 p. $109.95. hard caver. Price doesnot include sales tax. postage. andhandling.

(IndiVIdual issues afe $1.25 each)

This is not only a how-to guide. but acatalogue as well. The 1991 editioncontains over 2.000 environmentallyconscience. energy-efficient productssuch as an electric refrigerator whichuses one tenth the power of an ordinaryrefrigerator. and compact fluorescentlights thai produce four times the light ofincandescent lighting and last twentytimes as long. This catalogue is a blendof renewable energy supply options andillustrates efficient ways to use theenergy. Reulewed by Max Flanery.

ing systems. power storage and manage·men!. and conselVation and purificationsystems.

, 2 yrs. $20.00, 1 yr. $10.00

NAME

, RENEWAl; To receIve your magazille continuously. send in renewal 60 days beloreeXplralion date shown on your address label. (Example: EXP9112 meansthat the subscnption expires on receipt of December 1991 Issue.) Pleaseenclose address label from past Issue. Without an address label, renewalsubscriptions will take 3 10 4 monlhs to process.

CAlIFORNIA GEOLOOY r_als only hilin Inlormat'Qrl 'rom your malllllO label Of allach a label'rom a past issue

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TOTAL AMOUNT ENCLOSED: $ _

The 1991 edition of this sourcebookand catalogue focuses on energyeducation and contains a comprehensivecollection of energy-sensible technolo­gies. With this book readers can planindependently powered homes thatmaintain their accustomed comfortlevels. It demystifies solar. wind, andhydro-electric technologies. dealspractically with energy conselVation.and features complete step·by-stepinstructions for installing power generat-

ALTERNATIVE ENERGYSOURCEBOOK. 1991. Available from:Real GocxIs Trading Corporation. 966Mazzoni Street. Ukiah. CA 95482. 398p.. $14.00. paper cover.

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Your ordEll' subscnplton cannot be processed un~ss COfrect amount IS remllled All Fore>gn and Cana­dian orders must be paid With an Inlemallonal Money Order or Drall payable In United Slalas funds 10DlYlsoon of MTnes and Geology Address all Olden 10 OIVISION Of' MINES AND GEOLOGY. POIBo~ 2980. Sacramento. CahlOl....a 95812·2980

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Gold MlnlOg

STAKE YOUR CLAIM! How to AndGold and Stake a Mining Claim. ByMark G. Silva. 1990. Available from:High-Grade Publications. Box 995.Aptos. CA 95001. 105 p. $14.95(California residents add 6 3/4% salestax) plus $2.00 shipping, paper cover.

'" CALIFORNIA GEOlOGY JUNE 1991

• • • • • more Books

Over 10 million ounces of gold areexpected to be produced in 1990 Irom47 states. Mineral exploration andmining are possible on over 440 millionacres of public lane:!. Beginning goldhunters will find most of their basicquestions answered in this step-by-stepguide to locating potential gold depositsand filing a legal claim to the property.The book also includes standard claimforms, lists of pertinent State andFederal agencies, sources of governmentinformation and gold prospecting clubs.magazines. videos. and organizations.

HIstory

HISTORIC SPOTS IN CAUFORNIA.Fourth Edition. Revised by Douglas E.Kyle. 1990. Available from: StanfordUniversity Press. Stanford. CA 94305­2235. 617 p. $49.50. hard cover:$19.95. paper cover.

This book guides lhe reader ortraveler on a county-by-county tour ofhistorical Calilornia landmarks. Mileageand specific locations are given. Eachcounty's chapter proceeds in a chrono­logical vein, beginning with geography.continuing with Indian life. early Spanishsettlements. and moving on throughhistory into the twentieth century. Notintended as a history book per se. itdoes highlight historic landmarks andgives a chronicle of each. Mininglandmarks can be located quickly byconsulting the index under "Mines" and~Mining Camps.w Counties impacted bythe late 1800s gold rush receive detailedattention and include buildings and otherlandmarks from this era,

Igneous Geology

MAGMA -mANSPORT ANDSTORAGE. Edited by Michael P. Ryan.1990. John Wilcy & Sons. Inc., 605Third Avenue. New York. NY 10158.420 p.. $310.00. hard cover.

Over recent decades geologistsbecame increasingly aware of the needto understand how magma (molten rockcharged with gases) moves and behaves

at depth and at the surface. Geologistsinterested in igneous processes alsowanted to determine actual causes 01 thestructural features seen in volcanic andplutonic rocks in the field. The workinghypothesis is that knovJledge of thesestructural features can be combined withmineral. textural. trace element con­tents. and Isotope ratios of specificelements to yield information about thetemperatures and pressures at whichmagma forms. how magma forms. howthe magma gets to the surface or isemplaced at depth. and the nature of theconduits from magma chambers tocenters of eruption. One of the manyreasons the knowledge of magmatransport and storage is important togeologists is that it leads to an under­standing of the behavior of volcanoesand volcanic eruptions.

This book is a collection of articles byspecialists in the fields of continuummechanics, fluid dynamics. computa­tional fluid dynamics. heat transfer.experimental high-pressure geophysics.seismology. seismic tomography,volcanology. geodesy. field geology. andstructural geology. These specialislsdiscuss theoretical approaches to basicgeologic questions about magmamovement and storage. lbey thencompare their theoretical \AIOrk withactual field evidence 10 see how well thetheory explains what is observed in thefield. They also compare their theoreti­cal \AIOrk with indirect observations. Forexample. magma bodies can frequentlybe detected by analyzing; (I) bulging ofthe Earth's surface. (2) clustering ofsmall earthquakes. (3) attenuation ofseismic signals through magma cham­bers. and (4) differences in seismicvelocity along specific paths around andthrough magma chambers (a systemknown as seismic tomography).

While this is an advanced text. thediscussions include interesting andproductive treatment of some of theEarth's most fascinating phenomena.The concepts presented in this bookadvance our understanding of manyparameters controlling magma move­ment and storage. Reviewed by DaleStickney.

Mother lode Geology

YOSEMITE AND rnE MOrnERLODE GOLD BELT: Geology. Tecton­ics. and the Evolution of HydrothermalAuids in the Sierra Nevada of California.Edited by Leslie A. Landefeld andGeoffrey G. Stone. 1990. Availablefrom: Publications Committee. PacificSection AAPG. P.O. Box 631. Ventura.CA 93002. 200 p. $21.50 (incluclingshipping and handling). paper cover.Make check payable to: PublicationsPacific Section AAPG.

The discovery of gold in 1848 foreverchanged the landscape and history ofCalifornia. Placer mining. hydraulicmining. hard rock mining. and dredgemining served to remove millions ofounces of gold from the Sierra Nevada.The quest lor gold has not stopped.Mother Lode mining activity hasreturned after a 30-year hiatus followingWorld War n. More than 230.000ounces of gold have been mined since1985. Today. geologists continue tostudy the structural, stratigraphic. andchemical processes that formed theMother Lode in order to locate additionalgold ore deposits. Additionally. geologicinvestigations and mining operations arecarried out within a framework of localgovernment and public concerns as wellas State and Federal permitting require­ments.

This field guide is adapted from theannual meeting of the AmericanAssociation of Petroleum Geologists(held in San Francisco in June 1990) andis organized into two parts. Part 1contains three road logs that sample thegeologic and mining history of theMother Lode from Yosemite to Coloma.The road log stops describe the tectonicand structural forces that formed thegold deposits within the Mother Lode.Part 2 contains articles covering thegeology. mineral land classification. andmine permitting procedures within theFoothills Metamorphic Bell. Part 2 alsoincludes descriptions of six mines: PineTree-Josephine. H;lIvard. Royal­Mountain King. Carson Hill. Gold CUff.and Uncoln.x

CALIFOONIA GEOLOGY JUNE 1991 '"

STATE OF CALIFORNIATHE RESOURCES AGENCY

DEPARTMENT OF CONSERVATION

CALIFORNIA GEOLOGYDIVISION OF

MINES AND GEOLOGYPO,60X2980

SACRAMENTO, CALIFORN!A 95812·2980

USPS 350 840

ADDRESS CORRECTION REOUESTED

MEMORIALJoseph F. Poland

1908-1991

J oseph Fairfield Poland, an internationally recognizedauthority of land subsidence, died June 4, 1991 althe

age of 83, Poland earned his bachelor's degree in geologyfrom Harvard University in 1929 and his master's degreefrom Stanford University in 1935, His friends point out thathe had one of the longest graduate careers on record,Ahhough he completed his doctoral studies and oralexaminations at Stanford in the late 19305, Poland lacked awritten dissertation when he joined the U,S. GeologicalSurvey in 1940. It was not until 1981. when his fonner co­workers at the Survey submitted 40 years of research papersand reports. did Poland receive his doctorate from StanfordUniversity.

While at Stanford. Poland became interested in ground­water. In 1940 he joined the U.S. Geological Survey'sGround Waler Branch in Long Beach and later transferredto the Survey's Sacramento office where he directed aresearch program on land subsidence caused by groundwaterwithdrawal.

After retiring from the Survey in 1974. Poland continuedworking as a groundwater consultant. One of his manyaccomplishments was the explanation of why Venice, llalywas sinking; he became known to the Itallans as the "healer~

and ~savior~ of the city, Over several years of obs€lvation.Poland detennined that the Santa Dara Valley was sinkingat an average rate of 4 inches per year due to extensivegroundwater pumping. He also made many contributionsfrom his investigations of sea water intrusion into coastalaquifers of California. investigations of subsidence in the SanJoaquin Valley. and investigations of subsidence in theWilmington-Long Beach harbor area, :x

CALIFORNIA GEOLOGY

SECONO CLASS POSTAGE PAIDAT SACRAMENTO, CALIFORNIA

Dr. Poland standing at the approximate point of maximumground subsidence in the San Joaquin Valley. Subsidence ofapproximately 30 feet occurred from 1925 to 1977 due toaquifer compaction caused by groundwater pumping. Signsindicate the fanner elevations of the land surface in 1925.1955. and 1977. Photo taken in December 1977. Phoro byRichard Ireland, courtesy of the U.S. Geological Survey.

JUNE 1991