UNITED STATES DEPARTMENT OF THE INTERIOR 

GEOLOGICAL SURVEY

GEOLOGIC MAP OF THE LITTLE HUNTOON VALLEY QUADRANGLE, 

MINERAL COUNTY, NEVADA

By J. H. Stewart, F. J. Kleinhampl, R. C., Speed, 

and D. C. Johannnesen

Open-File Report 84-503

Prepared in cooperation with Nevada Bureau of Mines and Geology

This map is preliminary and has not been 

reviewed for conformity with U.S. Geological 

Survey editorial standards and stratigraphic 

nomenclature
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DESCRIPTION OF MAP UNITS

LITTLE HUNTOON VALLEY 

Qa ALLUVIAL DEPOSITS

Qtr SPRING DEPOSITS Travertine, sand, and alkali salts 

Qt TALUS 

Qpg PEDIMENT GRAVEL 

Qls LANDSLIDE DEPOSITS 

QToa OLDER ALLUVIAL DEPOSITS 

Tb BASALT

Ts TUFFACEOUS SILTSTONE, SANDSTONE, AND CONGLOMERATE Includes a 

volcanic subunit:

Tsab Andesitic basalt 

Tw WELDED TUFF, UNDIVIDED

Ttjs TUFF OF JACK SPRING Ash-flow tuff, crystal rich, not examined 

petrographically but abundant sanidine and biotite can be 

identified with hand lens, and Gilbert and others (1968, p. 285) 

report that calcic oligoclase is also a component in correlative 

rocks in Huntoon Valley quadrangle to the west. Sparse finegrained lithic fragments. Dark vitrophyre commonly occurs near 

base. Correlative rocks in Huntoon Valley quadrangle are 11.1 

to 11.7 m.y. old on the basis of K-Ar dating (Gilbert and 

others, 1968)

Ta ANDESITE FLOWS OR FLOWS OF INTERMEDIATE COMPOSITION

Tha ' HORNBLENDE ANDESITE Needle-shaped crystals of hornblende as much as 

1 cm long in aphanitic matrix

Tabx ANDESITE BRECCIA (lahar) Includes some sedimentary rocks

TJr RHYOLITE Massive, locally flow banded, phenocrysts of quartz and 

feldspar in aphanitic matrix; includes some raicrodiorite west of 

Jacks Spring Canyon. Probably mainly intrusive

Ttcjbx BRECCIA Probably a tectonic breccia. Composed of fragments, as 

much as several meters across, of Candelaria Junction Tuff of 

Speed and Cogbill (1979). Underlain, along a fault contact, by 

pre-Tertiary rocks and overlain, along a fault contact, by Tt2d 

or Tt^z. Relation to andesite breccia (Tabx) uncertain, but 

breccia (Tt 5 bx) probably older
Tt 5 CANDELARIA JUNCTION TUFF OF SPEED AND COGBILL (1979) Ash flow tuff, 

pale-red to grayish red; 18 percent crystals; plagioclase, 

sanidine, quartz in approximate proportions 2:2:3; sparse 

biotite; common flattened pumice; cliff forming: 22 to 24 m.y. 

old based on K-Ar dating (Speed and Cogbill, 1979). See Speed 

and Cogbill (1979) and Stewart (1979) for more detailed 

description.

Tt 3 b ANDESITE BRECCIA (LAHAR) Composed of slightly rounded fragment of 

mafic lava as much as 1 m in diameter set in a fine- to coarsegrained volcanic sand matrix

TUFF OF EASTSIDE MINE Very pale orange to pale yellowish brown; 15 

percent crystals; plagioclase, sanidine, and quartz in 

approximate proportions 6:4:3, sparse biotite and opaque 

minerals: 5 percent lithic fragments as large as 5 to 8 cm in 

diameter composed of the following: brown porphyritic lava, 

aphanitic lava, and sparse Paleozoic rocks. Common pumice. 

Mostly nonwelded to slightly welded

Ttoz ASH-FLOW TUFF Very pale orange to gray, crystal-poor, quartz and 

biotite identified in hand specimen. This tuff apparently does 

not occur in the Columbus, Miller Mountain, Basalt, Jack Spring, 

or Teels Marsh quadrangles, but conceivably could occur within 

poorly studied ash-flow tuff sequences in the central part of 

the Huntoon Valley quadrangle

Tt 2 d METALLIC CITY TUFF OF SPEED AND COGBILL (1979) Ash-flow tuff, dark 

gray in lower part, light gray in upper part; 25 percent 

crystals; plagioclase, sanidine, and quartz in approximate 

proportions 14:3:4; 2.7 percent biotite; sparse hornblende and 

opaque minerals; 1.6 percent rock fragments; cliff forming; 22 

to 24 m.y. old based on K-Ar dating (Gilbert and others, 

1968). See Speed and Cogbill (1979) and Stewart (1979) for more 

detailed description

Khv GRANODIORITE OF HUNTOON VALLEY Light- to medium-gray medium- to 

coarse-grained equigranular to porphyritic hornblende biotite 

granodiorite. Average mineral composition, in percent: quartz 

(19), potassium feldspar (17), plagioclase feldspar (49), mafic 

minerals (15). Distinguished from adjacent plutonic rocks by a 

gray topsoil and biotite flakes as large as 8 mm across. Sodic 

andesine (An^) crystals are subhedral to euhedral, as long as 

4.5 mm, and snow normal zoning; cores of some of crystals are 

sericitized. Myrraekite is uncommon. Microcline and microcline 

perthite are subhedral and as long as 1 cm. Quartz is as large 

as 3 mm in diameter. Brown biotite, as much as 8 percent of 

rock, occurs in cores of hornblende crystals and as individual 

flakes as large as 8 mm. Green hornblende, as much as 6 percent 

of rock, and averaging 3 percent is subhedral to euhedral and as 

long as 3.5 mm. Small amounts of green chlorite occur as 

distinct flakes or alteration products of biotite. Other 

minerals observed in small amounts (1 percent or less) include 

magnetite, sphene, and apatite. K-Ar ages of 86 m.y. (biotite)
and 100 and 101 ra.y. (hornblende) were obtained from samples 

collected in adjacent Rattlesnake Flat and Huntoon Valley 

quadrangles (Evernden and Kistler, 1970, loc. nos. 238, 239)

KJsm GRANITE OF SILVER MOON Medium- to coarse-grained, leucocratic, 

color index about 3 or less. Composition, in percent, based on 

one modal analysis: quartz (30), plagioclase (31), potassium 

feldspar (36), mafic minerals (3)

KJwf GRANITE OF WHISKEY FLAT Light-gray to pinkish-gray, medium- to 

coarse-grained porphyritic biotite granite. Average mineral 

composition, in percent: quartz (26), potassium feldspar (31), 

plagioclase feldspar (37), and mafic minerals (6). Rock 

weathers readily to coarse sandy grus. Oligoclase (An25) forms 

subhedral crystals as long as 4 mm that exhibit weak zoning and 

uncommon myrmekite intergrowths. Some twin lamellae are 

noticeably bent. Orthoclase(?)-perthite forms subhedral 

phenocrysts as long as 15 mm. Quartz crystals are anhedral and 

as much as 3.5 mm in diameter. Mafic minerals, constituting 2 

to 10 percent of rock, include chiefly biotite (as much as 8 

percent of rock but averaging 3 percent) and lesser amounts of 

hornblende. Biotite forms light-brown to brown subhedral 

crystals as long as 4 mm and is locally chloritized. Muscovite 

and sericite range in amount from a trace to as much as 8 

percent of rock, and their concentration in altered zones 

indicates a probable secondary origin related to hydrothermal 

alteration. Opaque minerals constitute as much as 2 percent of 

rock and include magnetite and hematite. Other minerals, from 

trace amounts as much as 1 percent of rock, include sphene, 

apatite, and zircon

KJdi DIORITE

KJd DUNLAP FORMATION Sedimentary rocks consisting of quartz sandstone, 

quartz-chert-feldspar sandstone, volcanic and chert clast 

sedimentary breccia, and red mudstone; depositional on Mina 

Formation(?) (Pmv); probably Cretaceous and/or Jurassic by 

lithic correlation with similar strata (Dunlap Formation) in the 

Huntoon Valley quadrangle dated as Early Jurassic (Stewart and 

others, 1981) and in the eastern Excelsior Mountains dated as 

mid-Cretaceous (Speed and Kistler, 1980)

T& c CANDELARIA FORMATION Light-brown, pale-olive-brown, dusky-brown, 

yellow-brown to greenish-gray siltstone to very fine grained 

sandstone, micaceous, evenly laminated to very thin bedded. 

Conspicuous cleavage parallel and in places across bedding. 

Sandstone is locally quartzitic. Coarse sandstone containing 

abundant dark-gray chert grains noted as float in one area. 

Gray chert, in layers from 2.5 to 7.0 cm thick, occurs in one 

area. Contact with Palmetto Formation at color change from gray 

and black of Palmetto to brown of Candelaria. In detail, 

contact is not distinct, and no conglomerate occurs near 

contact. Strata of the Palmetto Formation appear to be more 

structurally contorted than those of the Candelaria Formation
Pmv MINA FORMATIONC?) Interbedded volcanogenic sedimentary rocks and 

volcanic breccia and abundant mafic porphyry intrusions. 

Sedimentary rocks are mainly mudstone, thin-bedded feldspathic 

turbidite, and minor medium bedded pyroxene-rich volcanogenic 

sandstone. Breccia includes monolithologic deposits of coarseand fine-grained pyroxene porphyry, aphanitic igneous rocks, 

scoria, and microporphyry; breccias also polymict, containing 

fragments of porphyry, mudstone, and turbidites in matrices of 

feldspathic mudstone and crystal tuff; origins of breccias by 

primary volcanic extrusion, slump, and intrusion. Intrusive 

rocks are mainly small irregular bodies of pyroxene porphyry. 

Main differences from Mina Formation are absence of chert, 

predominance of very fine grained sedimentary rocks and 

abundance of primary igneous rock; contact with Mina Formation 

apparently depositional but stratigraphic relations uncertain

Pro MINA FORMATION Interbedded volcanogenic sedimentary rocks, chert, 

and igneous breccia; local intrusions of mafic porphyry. 

Clastic rocks: medium- to thick-bedded massive and plane 

laminated sandstone consisting of pyroxene, plagioclase, and 

clasts of feldspar-pyroxene porphyry; thin- to medium-bedded 

feldspathic turbidite; red mudstone; pebbly volcanogenic 

sandstone with mudclasts and fragments of porphyry; chert, 

medium to thick bedded and grainy, and probably of diagenetic 

rather than biogenic origin. Minor igneous breccia consists of 

massive deposits of mafic microporphyry and scoria; locally 

contains mudclasts. Intrusions are small irregular masses and 

dikes that locally include twisted fragments of sedimentary 

rocks and that invade wall rocks with structures suggesting 

emplacement before lithification and dewatering. Age is 

probably Permian by correlation with dated rocks in eastern 

Excelsior Mountains (Speed, 1977)

Op PALMETTO FORMATION Light-gray shale and medium- to dark-gray bedded 

chert. Sparse yellow-brown fine-grained quartzite that locally 

contains medium to coarse quartz grains. Unit locally exhibits 

intense deformation

Locality Fl (see southeast corner of map) Graptolites, 

identified by R. J Ross, Jr., U.S.G.S. Colln. D2963 CO, Field 

No. 1-60-13J. Fossils in Palmetto Formation, gray chert with 

light-gray shale. E379,170ra, N4,222,350m. Graptolites: 

Orthograptus quadrimucronatus Hall and Climacograptus sp. (width 

1.5 mm; th - 14/10 mm; no proximal ends preserved). Age: Best 

estimate is zone of _0_. quadrimucronatus of Berry, generally 

considered late Caradocian.
REFERENCES

Evernden, J. F., and Kistler, R. W., 1970, Chronology of emplacement of 

Mesozoic batholithic complexes in California and western Nevada: U.S. 

Geological Survey Professional Paper 62.3, 42 p.

Gilbert, C. M., Christiansen, M. N., Al-Rawi, Y. , and Lajoie, K. R., 1968, 

Structural and volcanic history of Mono Basin, California-Nevada, in 

Coats, R. R., Hay, R. C., and Anderson, C. A., eds., Studies in 

volcanology: Geological Society of America Memoir 116, p. 275-329.

Speed, R. C., 1977, Excelsior Formaiton, west-central Nevada; stratigraphic 

appraisal, new divisions, and paleogeographic interpretations, in 

Stewart, J. H., Stevens, C. H., and Fritsche, A. E., eds., Paleozoic 

Paleogeography of the western United States: Society of Economic 

Paleontologists and Mineralogists, Pacific Section, Pacific Coast 

Paleogeographic Symposium 1, p. 325-336.

Speed, R. C., and Cogbill, A. H., 1979, Cenozoic volcanism of the Candelaria 

region, Nevada: Geological Society of America Bulletin, pt. II, v. 90, 

p. 456-493.

Speed, R. C., and Kistler, R. W., 1980, Cretaceous volcanisra, Excelsior 

Mountains, Nevada: Geological Society of America Bulletin, pt. 1, v. 91, 

p. 392-398.

Stewart, J. H., 1979, Geologic map of the Miller Mountain and Columbus 

quadrangles, Mineral and Esmeralda Counties, Nevada: U.S. Geological 

Survey Open-File Report 79-1145, scale 1:24,000.

Stewart, J. H., Kleinhampl, F. J., Johannesen, D. C., Speed, R. C., and 

Dohrenwend, J. C., 1981, Geologic map of the Huntoon Valley quadrangle, 

Mineral County, Nevada and Mono County, California: U.S. Geological 

Survey Open-File Report 81-274, scale 1:62,500.