Mineral Resources of tbeTwin Peaks 

Wilderness Study Area/Washoe County, 

Nevada, and Lassen County, California

U.S. GEOLOGICAL SURVEY BULLETIN 1706-A

Chapter A

Mineral Resources of the

Twin Peaks Wilderness Study Area,

Washoe County, Nevada,

and Lassen County, California

By THOMAS L VERCOUTERE, MARTIN L. SORENSEN, 

JAMES G. FRISKEN, and DONALD PLOUFF 

U.S. Geological Survey

MICHAEL S. MILLER 

U.S. Bureau of Mines

U.S. GEOLOGICAL SURVEY BULLETIN 1706

MINERAL RESOURCES OF WILDERNESS STUDY AREAS: NORTHEASTERN 

CALIFORNIA AND PART OF ADJACENT WASHOE COUNTY, NEVADA
DEPARTMENT OF THE INTERIOR 

DONALD PAUL MODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1988

For sale by the

Books and Open-File Reports Section

U.S. Geological Survey

Federal Center, Box 25425

Denver, CO 80225

Library of Congress Cataloging-in-Publication Data

Mineral resources of the Twin Peaks Wilderness Study 

Area, Washoe County, Nevada, and Lassen County, 

California.

Mineral resources of wilderness study areas northeastern

California and part of adjacent Washoe County,

Nevada, Ch. A; U.S. Geological Survey Bulletin 1706-A

Bibliography

Supt. of Docs. No.: I 19.3:1706-A

1. Mines and mineral resources Twin Peaks Wilderness

(Nev. and Calif.) 2. Twin Peaks Wilderness (Nev. and

Calif.) I. Vercoutere, Thomas L. II. Series. III. Series:

U.S. Geological Survey Bulletin 1706-A.

QE75.B9 No. 1706-A 557.3 s 87-600404

[TN25.T9] [553'.09793'55]
STUDIES RELATED TO WILDERNESS

Bureau of Land Management Wilderness Study Areas

The Federal Land Policy and Management Act (Public Law 94-579, October 21,1976) requires the U.S. 

Geological Survey and the U.S. Bureau of Mines to conduct mineral surveys on certain areas to determine the 

mineral values, if any, that may be present. Results must be made available to the public and be submitted to 

the President and the Congress. This report presents the results of a mineral survey of part of the Twin Peaks 

Wilderness Study Area (CA-020-619A), Washoe County, Nevada, and Lassen County, California.

CONTENTS

Summary Al

Abstract 1

Character and setting 1

Identified resources and mineral resource potential 1 

Introduction 2

Area description 3

Previous and present studies 3

Acknowledgments 3 

Appraisal of identified resources 3

Mining and mineral exploration history 3

Mines, mining claims, and mineralized areas 4

Mineral economics 4 

Assessment of mineral resource potential 5

Geology 5

Geochemistry 5

Geophysics 6

Mineral resource assessment 7 

References cited 7 

Appendixes

Definition of levels of mineral resource potential and certainty of assessment 11

Resource/reserve classification 12

Geologic time chart 13

FIGURES

1. Index map showing location of Twin Peaks Wilderness Study Area, Washoe County, Nevada, and Lassen 

County, California A2

2. Map showing generalized geology and mineral resource potential of Twin Peaks Wilderness Study Area, 

Washoe County, Nevada, and Lassen County, California 4

Contents V

MINERAL RESOURCES OF WILDERNESS STUDY AREAS: NORTHEASTERN 

CALIFORNIA AND PART OF ADJACENT WASHOE COUNTY, NEVADA

Mineral Resources of the 

Twin Peaks Wilderness Study Area, 

Washoe County, Nevada, and 

Lassen County, California

By Thomas L. Vercoutere, Martin L. Sorensen, James G. Frisken, 

and Donald Plouff 

U.S. Geological Survey

Michael S. Miller 

U.S. Bureau of Mines

SUMMARY

Abstract

At the request of the Bureau of Land Management, 50,570 

acres of the Twin Peaks Wilderness Study Area (CA-020-619A) 

located in northwestern Nevada and northeastern California 

were evaluated for mineral resources (known) and mineral 

resource potential (undiscovered). In this report, the area studied 

is referred to as "the wilderness study area", or simply "the study 

area." The dominant rock types are basaltic and silicic volcanic 

rocks. There has been no mining activity, but 30 million tons of 

subeconomic pozzolan is inferred within the study area. The 

southeastern and southwestern parts of the study area have a high 

resource potential for pozzolan. A small area in the north-central 

part of the study area has moderate resource potential for gold in 

altered basalt breccia. Rocks exposed throughout the study area 

have low resource potential for copper, tungsten, and zinc. No 

geothermal leases exist, and the study area has low potential for 

geothermal resources. The study area has a low resource 

potential for oil and gas. The southwestern, southeastern, and 

eastern parts of the study area have low resource potential for 

sand and gravel.

Washoe County, Nev., and Lassen County, Calif., about 70 mi 

north of Reno, Nev. The study area is within a region 

characterized by north-trending block-faulted mountain 

ranges and extensive plateau-forming basalt flows. Twin 

Peaks (fig. 1), the dominant physiographic feature of the area, 

is the eroded remnant of a small shield volcano thought to be 

the source of many of the basalt flows in the region (Bonham, 

1969). The eroded flanks of Twin Peaks and several deeply 

incised creeks provide good exposures of the Tertiary and 

Quaternary volcanic, intrusive, and sedimentary rocks. The 

oldest of these rocks are late Miocene and (or) Pliocene silicic 

volcanic rocks that are part of Bonham's (1969) informally 

named High Rock sequence. These silicic rocks are overlain 

by latest Miocene and Pliocene basalt and basaltic andesite 

flows that are intercalated with sandstone, conglomerate, and 

basaltic scoria. Dikes and plugs of basalt and andesite intrude 

the volcanic and sedimentary rocks. Young deposits, areally 

restricted to valleys and basin margins, include Pliocene and 

(or) Pleistocene basalt flows and alluvial fan deposits, Pleistocene lake deposits, and Quaternary alluvium.

Character and Setting Identified Resources and Mineral Resource Potential

The Twin Peaks Wilderness Study Area is located along The Twin Peaks Wilderness Study Area has no known 

the northwestern edge of the Smoke Creek Desert in central mining history or visible evidence of mining activity. Thirty

Mineral Resources of the Twin Peaks Wilderness Study Area, Washoe County, Nevada, and Lassen County, California A1
million tons of subeconomic pozzolan resources are inferred in 

the southwest corner of the study area.

A small area south of Mixie Flat (fig. 2) in the northcentral part of the study area has moderate resource potential 

for gold in hydrothermally altered basalt breccia. The entire 

study area has low resource potential for copper, tungsten, and 

zinc. The southeast and southwest corners of the study area 

have high resource potential for pozzolan in tuffaceous lake 

sediments. No geothermal leases exist, and there is low 

potential for geothermal resources in the study area. The study

area has low resource potential for oil and gas. The southwestern, southeastern, and eastern parts of the study area have low 

resource potential for sand and gravel in Quaternary lake and 

stream deposits.

INTRODUCTION

This mineral survey was requested by the U.S. Bureau of 

Land Management (BLM) and is a joint effort by the U.S.

120°15' 120°00' 119°45I

40°45'|-

40°30' -

I r M\ ^ C""

APPROXIMATE BOUNDARY OF 

_ TWIN PEAKS WILDERNESS STUDY ' 

AREA (CA-020-619A) X \l

, i 

/ Shinn Mountain

Figure 1. Index map showing location of Twin Peaks Wilderness Study Area, Washoe County, Nevada, and Lassen 

County, California.

A2 Mineral Resources of Wilderness Study Areas Northeastern California and Part of Adjacent Washoe County, Nevada
Geological Survey (USGS) and the U.S. Bureau of Mines 

(USBM). An introduction to the wilderness review process, 

mineral survey methods, and agency responsibilities were 

provided by Beikman and others (1983). The USBM evaluates 

identified resources at individual mines and known mineralized areas by collecting data on current and past mining 

activities and through field examination of mines, prospects, 

claims, and mineralized areas. Identified resources are classified according to the system described by U.S. Bureau of 

Mines and U.S. Geological Survey (1980). Studies by the 

USGS are designed to provide a reasonable scientific basis for 

assessing the potential for undiscovered mineral resources by 

determining geologic units and structures, possible environments for mineral deposition, presence of geochemical and 

geophysical anomalies, and applicable ore-deposit models. 

Mineral-assessment methodology and terminology as they 

apply to these surveys were discussed by Goudarzi (1984). See 

the appendixes for the definition of levels of mineral resource 

potential and certainty of assessment and for the resource/ 

reserve classification.

Area Description

The part of the Twin Peaks Wilderness Study Area (C A020-619A) that the USGS and USBM studied at the request of 

the BLM encompasses approximately 50,570 acres of 

semiarid, grass- and sage-covered ridges and valleys in northwestern Nevada and northeastern California. The study area is 

north west of the Smoke Creek Desert (fig. 1) in the southeastern part of the Modoc Plateau subprovince of the Basin and 

Range physiographic province. Gravel roads and four-wheeldrive jeep trails leading from U.S. Highway 395, to the west, 

and Nevada Highway 81, to the northeast, provide access to the 

study area (fig. 1). Elevations range from 6,592 ft at the summit 

of Twin Peaks to approximately 4,000 ft along the southeastern 

margin of the study area. Several deeply incised canyons with 

perennial streams dissect the area and debouch into the basin 

of the Smoke Creek Desert.

Field investigations for this study wereconducted in 1985. 

The USGS field checked the published geologic maps and 

remapped most of the study area, evaluated published geochemical data (Barringer Resources, Inc., 1982), sampled 

selected areas for geochemical analysis, collected and evaluated gravity data, and evaluated aeromagnetic and radiometric 

data. The USBM researched pertinent literature, Washoe and 

Lassen County mining records, and files of the USBM, Nevada 

Bureau of Mines, California Division of Mines and Geology, 

and BLM for records of mining activity. The USBM collected 

15 placer and 59 rock samples from 17 mineralized sites in the 

study area. Three of the rock samples were examined petrographically.

Gold and silver analyses by the USBM were by combined 

fire assay-ICP (inductively coupled plasma analysis); other 

elements were analyzed by atomic absorption, colorimetry, 

radiometry, or X-ray fluorescence. Representative samples 

were analyzed for 40 elements by semiquantitative emission 

spectrophotometry. X-ray diffraction was used to screen 

selected samples for zeolite and clay minerals.

Nine samples of lake-sediment material were screened by 

the USBM for pozzolan suitability by analyzing oxide content 

for whole-rock composition (ICP) and loss on ignition. Two 

pozzolan samples were analyzed for pozzolan suitability by 

the U.S. Army Corps of Engineers, Vicksburg, Miss.

Alluvial (placer) samples were panned in the field and 

later concentrated in the laboratory. Detailed analytical procedures and results are given in Miller (1987). Detailed analyses 

are available from the USBM, Western Field Operations Center, E. 360 Third Ave., Spokane, WA 99202.

Acknowledgm ents

The authors gratefully acknowledge Leona Parker, John 

Keith, and Ernest Schofield of the Susanville BLM firedispatch center, for radio support, and George Wingate and 

Kenneth Davis of the BLM, Susanville, for providing helicopter support during field work for this study.

Previous and Present Studies

A report on the geology and mineral deposits of Washoe 

County (Bonham, 1969) provided preliminary information on 

the regional structure and stratigraphy. Information on the 

structural framework was supplemented by a report on the 

Modoc Plateau (MacDonald, 1966). A geochemical and 

geostatistical study prepared for the BLM by Barringer Resources, Inc. (1982) contains geochemical data for streamsediment samples collected from this study area.

Several topical studies pertinent to the study area have 

been written: Russell (1885) and Benson (1978) described the 

geologic history of Lake Lahontan, and Phalen (1919), Overton (1947), Smith (1956), andPapke (1970) discussed mineral 

resources of the region.

APPRAISAL OF IDENTIFIED RESOURCES

By Michael S. Miller 

U.S. Bureau of Mines

Mining and Mineral Exploration History

In 1911 and during the 1930's, at least 30 mining claims 

were staked outside the study area northwest of Mixie Flat, 

near the State boundary. Two other claims were staked about 

2 mi southeast of the area in 1946 for diatomite found in the 

tuffaceous lake sediments. Salt and other evaporites were 

produced on a small scale in the late 1800's and early 1900's 

a few miles southeast of the study area in the Smoke Creek 

Desert (Russell, 1885, p. 232-233; Phalen, 1919, p. 145-146).

Mineral Resources of the Twin Peaks Wilderness Study Area, Washoe County, Nevada, and Lassen County, California A3
In 1985, there were no active claims or mining activity within 

or near the study area (Miller, 1987).

Mines, Mining Claims, and Mineralized Areas

No mines or mining claims were found in the study area 

during this study (Miller, 1987). However, mineral-bearing 

sites containing small or low-grade concentrations of gold, 

silver, copper, lead, zinc, nickel, tungsten, zeolite, and clay are 

present, and there are at least 30 million tons of inferred 

subeconomic pozzolan resources identified in the study area.

Mineral Economics

No metallic minerals were visible at the sites of metallic 

geochemical anomalies indicated by Barringer Resources, Inc. 

(1982). The amounts of lead, zinc, silver, and copper in several 

USBM samples, particularly those from a kaolinitic basalt 

breccia at Mixie Flat, confirm the geochemical anomalies of 

Barringer Resources, Inc. (1982) and indicate possible hydrothermal mineralization systems in or near the study area. 

Gold, silver, copper, lead, zinc, and nickel contents of samples 

taken by the USBM (Miller, 1987) were one-tenth to onehundredth of the concentrations needed to be economic today.

APPROXIMATE BOUNDARY

OF 

TWIN PEAKS WILDERNESS

STUDY AREA

(CA-020-619A)

EXPLANATION

Area with high mineral resource potential 

Area with moderate mineral resource potential 

r I Area with low mineral resource potential 

x Identified pozzolan resource

See appendixes for definition of levels of mineral resource potential 

(L. M. H) and certainty of assessment (B, C. D)

Commodities

Au Gold O, G Oil and gas 

Cu Copper s, Gr Sand and gravel 

W Tungsten Pozzolan 

Zn Zinc

Geologic Map Units

Qa Alluvium (Quaternary)

Ql Tuffaceous lake sediments (Quaternary)

QTf Fanglomerates (Pleistocene and (or) Pliocene)

QTb Basalt flows (Pleistocene and (or) Pliocene)

Td Mafic and intermediate dikes and plugs (Pliocene)

Tb Basalt and basaltic andesite flows (Pliocene and late

Miocene) 

Ts Voteaniclastic sedimentary rocks (Pliocene and late

Miocene) 

TV Silicic and intermediate volcanic rocks, undivided

(Pliocene and (or) Miocene)

 - Contact

 Fault-Dashed where approximately located

 Dike

CORRELATION OF MAP UNITS

Figure 2. Generalized geology and mineral resource potential of Twin Peaks Wilderness Study Area, Washoe County, 

Nevada, and Lassen County, California. Geology by M.L. Sorensen and T.L. Vercoutere, 1985.

A4 Mineral Resources of Wilderness Study Areas Northeastern California and Part of Adjacent Washoe County, Nevada
Zeolite concentrations were lower than in typical deposits by 

a factor of about ten, and a kaolinite deposit at the breccia pipe 

south of Mixie Flat is too small to be economic. No volumes 

or tonnages of these materials were estimated.

Although an inferred 30 million tons of subeconomic 

pozzolan crops out in and near the study area and could be used 

as a replacement for cement in some concretes, ash from coalfired power plants currently supplies most domestic pozzolan 

requirements. Exploration, mining, and transportation costs 

(as of July, 1986) using the method of Benjamin and Gale 

(1984) for a 1-million-ton deposit mined at 500 tons per day 

with a 1:1 stripping ratio and 1 mi of truck transportation are 

estimated to be about $12.50 per short ton of pozzolan in the 

southwest corner of the study area. Probably the only domestic 

source of natural pozzolan being mined in 1985 was the extensive deposit of Lassenite Industries, Doyle, Calif., 50 mi 

southwest of the study area, at a railhead. Competition from 

coal ash and high transportation costs will probably keep the 

study area's pozzolan deposits subeconomic within the foreseeable future; the loss of ash supplies due to decreases in coal 

burning could improve natural pozzolan markets, as could 

nearby highway or dam construction.

Deposits of sand and gravel are found in many stream 

drainages throughout the study area, but are not classified as 

resources because of their small size and inaccessibility and 

because suitable deposits are located closer to potential markets.

ASSESSMENT OF MINERAL RESOURCE POTENTIAL

By Thomas L. Vercoutere, Martin L. Sorensen, 

James G. Frisken, and Donald Plouff 

U.S. Geological Survey

Geology

The Twin Peaks Wilderness Study Area lies in the southeastern part of the Modoc Plateau subprovince within the Basin 

and Range physiographic province (MacDonald, 1966). The 

Modoc Plateau subprovince consists of north-trending, blockfaulted ranges and intervening basins and contains numerous 

well-preserved constructional volcanic landforms.

The entire study area is underlain by Tertiary and Quaternary rocks (see geologic time chart in appendixes) that are 

either directly or indirectly volcanic in origin. They consist 

predominantly of basaltic and silicic flows, with mafic and 

intermediate dikes and plugs, and lenses of volcaniclastic 

sedimentary rocks that are intercalated with the basalt flows. 

Quaternary deposits are predominantly alluvial and lacustrine 

sediments. An areally restricted stack of basalt flows of 

Pliocene and (or) Pleistocene age (Bonham, 1969) is present in 

the western part of the study area.

The oldest rocks exposed in the study area are mapped as 

undifferentiated silicic and intermediate volcanic rocks (fig.

2). One of the two major rock types included within this unit 

is a bluish-white to light-gray rhyolite that includes less than 5 

percent phenocrysts of feldspar, quartz, biotite, and amphibole, all less than 0.2 in. long. The other major rock type in the 

unit is a pinkish-gray, fine-grained, porphyritic intrusive trachyandesite that has 5 to 10 percent of 0.1- to0.2-in. phenocrysts 

of plagioclase and biotite. These rocks are correlative with part 

of what Bonham (1969) designated as "undifferentiated High 

Rock Sequence and Intrusive Volcanic Rocks".

The most extensive unit in the study area consists of late 

Miocene and Pliocene olivine basalt and basaltic andesite 

flows (fig. 2) that typically are 3 to 60 ft thick. Columnar 

jointing is common and locally well developed. The basalt is 

aphyric to porphyritic, typically has phenocrysts of plagioclase 

(as long as 0.5 in.) and olivine, and is commonly vesicular. 

Basalt in this region emanated from numerous fissures and 

vents (Bonham, 1969). The generally consistent dip of the 

basalt flows away from Twin Peaks suggests that the peaks 

were volcanic vents.

Intercalated with the basalt flows are lenses of volcaniclastic sedimentary rocks (fig. 2) that include conglomerate, 

sandstone, silty sandstone, and reworked basaltic scoria. The 

bedding structure, internal deformation, and limited lateral 

extent indicate that these lenses were deposited in drainages 

and irregular basins of moderate to high relief that commonly 

contained lakes. Fragmentary fish, bird, mammal, and turtle 

fossils from a silty sandstone suggest that the intercalated sedimentary rocks were deposited during Early Pliocene time, 

probably between 3.5 and 5.0 million years ago (C.A. Repenning, written commun., 1987).

Pliocene basaltic to andesitic dikes and plugs intrude the 

Tertiary rocks of the study area and are clustered into three 

regions. A northwesterly striking dike system intrudes basalt 

in an area 2 to 5 mi north of the Smoke Creek Reservoir in the 

western part of the study area. A northerly striking dike-andplug system intrudes basalt and sedimentary rocks 1 to 4 mi 

southwest, west, and northwest of Twin Peaks. A less wellconstrained system has strikes that range from northwest to 

northeast and intrudes all three Tertiary rock units in the 

northeast quarter of the study area.

Other rock types exposed in the study area are Pliocene 

and (or) Pleistocene basalt flows along Smoke Creek in the 

western part of the study area and dissected fanglomerates in 

the southern part of the study area, Pleistocene tuffaceous lake 

sediments in the southeast and southwest corners of the study 

area, and Quaternary alluvium in active drainages.

Geochemistry

In 1982, Barringer Resources, Inc., published geochemical analyses for several thousand stream-sediment samples 

collected for a resource assessment in northwestern Nevada 

(Barringer Resources, Inc., 1982). Geochemical analysis of 

stream sediments is the principle method for reconnaissance

Mineral Resources of the Twin Peaks Wilderness Study Area, Washoe County, Nevada, and Lassen County, California AS
geochemical exploration in areas where an integrated drainage 

system has developed (Meyer and others, 1979). The geochemical data obtained are a function of the composition of the 

rocks, sediments, and waters within the upstream catchment 

area. For the present study, analyses of 28 rock and 4 streamsediment samples collected by the USGS and 111 of 

Barringer's analyses of stream-sediment samples collected in 

the study area were used. The USGS rock and stream-sediment 

samples were analyzed by semiquantitative emission-spectrographic methods (Grimes and Marranzino, 1968). Details of 

the analytical procedures andresultsof theUSGS sampling are 

presented in Adrian and others (1987). All of Barringer's 

stream-sediment samples were analysed by inductively 

coupled plasma analysis (ICP), fluorimetric and colorimetric 

methods, and atomic-absorption spectroscopy and spectrophotometry appropriate for the elements desired. More specific information on the analytical procedures can be found in 

the original report (Barringer Resources, Inc., 1982). Their 

results for the 111 stream-sediment-sample analyses were 

statistically evaluated and histograms were made for each 

element present at concentrations above the detection limit. 

Concentrations were considered anomalous for each of the 

elements when the values were greater than two standard 

deviations above the mean for that element.

An area along the north boundary of the study area south 

of Mixie Flat (fig. 2) shows evidence of hydrothermal alteration. This area is underlain by a pipe-like structure approximately 200 ft in diameter that consists of brecciated basalt in 

a kaolinite matrix. Rock samples collected from this area 

contain anomalous concentrations of copper (130 parts per 

million, ppm), lead (31 ppm), zinc (180 to 200 ppm), and gold 

(0.075 ppm). A stream-sediment sample collected nearby also 

contains anomalous concentrations of copper, zinc, chromium, and tungsten; concentrations of these elements diminished in samples collected progressively downstream. The 

remainder of the rocks exposed within the study area have no 

visible evidence of mineralization or hydrothermal alteration. 

The Barringer study reported anomalous concentrations of 

barium, copper, tungsten, and zinc in stream-sediment samples 

collected from localities throughout the study area (Barringer 

Resources, Inc., 1982). These anomalous concentrations are 

all less than three standard deviations from the mean and 

represent concentrations no greater than an order of magnitude 

above normal crustal abundance reported by Turekian (1977). 

Stream-sediment samples containing anomalous concentrations of mercury (18 to 28 parts per billion, ppb) were collected 

from drainages in the southeastern part of the study area. While 

these values are considered anomalous in the study area, they 

do not represent a significant increase over the average of 9 or 

10 ppb concentration typically found in basalts (Turekian, 

1977), and the variation in mercury content within the study 

area may only represent variation in magmatic concentration. 

Copper content in 27 of the 28 basaltic dikes analyzed is less 

than 70 ppm; one dike has an anomalous concentration of 

copper (300 ppm).

Geophysics

The results of a regional aeromagnetic survey for the 

Nevada part of the study area (U.S. Geological Survey, 1972) 

indicate that the average magnetic intensity level is about 200 

to 300 nanoteslas (nT) higher than the regional intensity levels 

in surrounding areas. A broad magnetic high with two crests 

covers most of the southern hah0 of the study area. The 

amplitude of the magnetic high is about 400 nT. The broad 

magnetic high generally reflects the high regional elevation of 

the study area because the flight level here is closer to the 

normally magnetized volcanic rocks than when over the surrounding areas. The presumed volcanic vent at Twin Peaks is 

located along the north-northwest-trending axis of the eastern 

crest of the broad magnetic high. The saddle in the magnetic 

high is located along a north-northwest-trending line between 

Burro Creek at the south edge of the study area and Mixie Rat 

outside the north edge of the study area. Closed magnetic lows 

occur at both ends of the line segment. The location of the 

magnetic saddle does not strongly correlate with topography, 

as would be expected where the surface rocks have significant 

magnetization. Therefore, the magnetic saddle probably reflects rocks of lower magnetization beneath the volcanic rocks 

exposed at the surface. Cenozoic volcanic rocks may form a 

relatively thin veneer over a structural or erosional high of lessmagnetic pre-Cenozoic basement rocks along the saddle.

In 1985, 10 gravity stations in the study area and 17 

stations within 3 mi of the study area boundary were established by the USGS and were combined with 4 previously 

established stations in California (Snyder and others, 1982) 

and 2 in Nevada (Alien H. Cogbill, written commun., 1985). A 

preliminary Bouguer gravity-anomaly map (Plouff, unpub. 

data) displays a conspicuous gravity high that coincides with 

the previously discussed magnetic saddle, both extending 

about 5 mi south of the study area. The gravity high and 

alignment of, magnetic lows may reveal the location of a preCenozoic basement high that incorporates rocks that are denser 

and less magnetic than surrounding Cenozoic rocks. The east 

flank of the high forms the west edge of a gravity low centered 

more than 4 mi southeast of the study area, over the north end 

of the Smoke Creek Desert. A northwestward decrease of 

about 2.5 milligals per mile, starting near the southeast edge of 

Mixie Rat, forms another conspicuous gravity anomaly. 

Gravity contours within this gradient are approximately linear 

and may indicate underlying deep-seated fault control.

Radiometric data were compiled by Geodata International, Inc. (1978), in Nevada and by Western Geophysical 

Company of America (1981) in California for the National 

Uranium Resource Evaluation (NURE) program of the U.S. 

Department of Energy. The coverage of the study area in 

Nevada consists of three east-west flightlines and one northsouth flightline totaling about 31 mi. No flightlines crossed the 

part of the study area in California. Recordings were made of 

gamma-ray flux from radioactive isotopes of uranium, thorium, and potassium. Count rates about one standard deviation

A6 Mineral Resources of Wilderness Study Areas Northeastern California and Part of Adjacent Washoe County, Nevada
above mean background level for all three isotopes were 

recorded near and to the east of Grass Mountain, along a 

flightline located 2 mi south of the northmost edge of the study 

area. The cause of this anomaly is likely to be higher radioactivity emanating from the silicic volcanic rocks. Ground-based 

scintillometer readings showed the gamma-ray flux at outcrops of the silicic volcanic rocks to be greater than that at 

outcrops of the surrounding mafic rocks. Along the west half 

of the flightline that is located 0.5 mi north of the south edge 

of the study area, count rates for all three isotopes were one 

standard deviation below mean background level. The low 

values may be an effect of rock alteration.

Mineral Resource Assessment

Geologic, geochemical, and geophysical investigations 

suggest limited mineral resource potential in the wilderness 

study area (fig. 2). Hydrothermally altered basalt breccia 

collected by the USBM from south of Mixie Flat contains 

detectable gold (0.075 ppm). This area has moderate resource potential for gold, certainty level B.

The entire study area has a low resource potential for 

copper, tungsten, and zinc, certainty level B. The rating is 

based on anomalous concentrations of these elements in 

stream-sediment and rock samples.

Quaternary tuffaceous lake sediments exposed in the 

southeast and southwest corners of the study area have a high 

resource potential for pozzolan, certainty level D, in addition 

to the 30 million tons of inferred subeconomic pozzolan 

resources already identified.

Although hot springs occur in adjacent ranges, no evidence of geothermal activity was seen in or near the study area. 

No geothermal leases exist in the Twin Peaks Wilderness 

Study Area. The area has low potential, certainty level B, for 

geothermal resources.

The potential for oil and gas resources in the study area is 

low, certainty level C. This evaluation is based on the absence 

of organic-rich rocks that might be a source of hydrocarbons 

and the lack of suitable reservoir rocks. 

The potential for sand and gravel resources in the southwestem, southeastern, and eastern study area is low, certainty level 

C, in the Quaternary alluvium.

REFERENCES CITED

Adrian, B.M., Frisken, J.G., Fey, D.L., Malcolm, M.J., and Taylor, 

C.D., 1987, Analytical results and sample locality map of 

stream-sediment, heavy-mineral-concentrate, and rock 

samples from the Twin Peaks (CA-020-61 9A) Wilderness 

Study Area, Lassen County, California, and Washoe County, 

Nevada: U.S. Geological Survey Open-File Report87-266, 

19 p., scale 1:48,000.

Barringer Resources, Inc., 1 982, Geochemical andgeostatistical 

evaluation of wilderness study areas, Winnemucca district, 

northwest Nevada: Contract YA-553-CT1-1 096 prepared 

for the U.S. Bureau of Land Management.

Be i km an, H.M., H inkle, M.E., Frieders, Twi la, Marcus, S.M., and 

Edward, J.R. 1 983, Mineral surveys by the Geological Survey and the B ureau of Mines of Bureau of Land Management 

Wilderness Study Areas: U.S. Geological Survey Circular 

901, 28 p.

Benjamin, D.A., and Gale, George, 1984, MLA costing procedures for classification of mineral resource: unpublished 

report available at Western Field Operations Center, U.S. 

Bureau of Mines, E. 360 Third Avenue, Spokane, WA 

99202; 60 p., includes BASIC computer program.

Benson, L.V., 1978, Fluctuation in the level of pluvial Lake 

Lahontan during the last 40,000 years: Quaternary Geology, v. 9, p. 300-318.

Bonham, H.F., 1969, Geology and mineral deposits of Washoe 

and Storey Counties, Nevada: Nevada Bureau of Mines 

Bulletin 70, 140 p.

Geodata International, Inc., 1 978, Aerial radiometric and magnetic survey, Lovelock national topographic map, Nevada: 

U.S. Departmentof Energy Open-file Report GJBX-125 (78), 

v. 2, 69 p.

Goudarzi, G.H., 1984, Guide to preparation of mineral survey 

reports on public lands: U.S. Geological Survey Open-File 

Report 84-787, 51 p.

Grimes, D.J., andMarranzino, A.P., 1968, Direct-currentarcand 

alternating-current spark emission spectographic field 

methods for the semiquantitative analysis of geologic materials: U.S. Geological Survey Circular 591, 6 p.

MacDonald, G.A., 1966, Geology of the Cascade Range and 

Modoc Plateau, in Bailey, E.H., ed., Geology of northern 

California: California Division of Mines and Geology Bulletin 190, p. 65-96.

Meyer, W.T., Theobold, P.K., Jr., and Bloom, H., 1979, Stream 

sediment geochemistry, in Hood, P.J., ed., Geophysics and 

geochemistry in the search for metallic ores: Geological 

Survey of Canada Economic Geology Report 31, p. 411- 

443.

Miller, M.S., 1987, Mineral resources of the Twin Peaks Wilderness Study Area, Washoe County, Nevada, and Lassen 

County, California: U.S. Bureau of Mines, Mineral Land 

Assessment, Open-File Report 15-87, 31 p.

Overton,T.D., 1 947, Mineral resourcesof Douglas, Ormsby, and 

Washoe Counties, Nevada: Nevada Bureau of Mines Bulletin 46, 88 p.

Papke, K.G., 1970, Montmorillonite, bentonite, and Fuller's 

earth deposits in Nevada: Nevada Bureau of Mines Bulletin 

76, 47 p.

Phalen, W.C., 1919, Salt resources of the United States: U.S. 

Geological Survey Bulletin 669, 284 p.

Russell, I.C., 1885, Geological history of Lake Lahontan, a 

Quaternary lake of northwestern Nevada: U.S. Geological 

Survey Monograph 11, 288 p.

Smith, A.M., 1956, Resource report, Washoe County, NV, 1 956: 

Office of George W. Malone, United States Senate, Nevada, 

State of Nevada, County Report, 166 p.

Snyder, D.B., Roberts, C.W.,Saltus, R.W., and Sikora, R.F., 1982, 

Magnetic tape containing the principal facts of 60,026

Mineral Resources of the Twin Peaks Wilderness Study Area, Washoe County, Nevada, and Lassen County, California A7
gravity stations in the State of California: National Technical Information Service, U.S. Department of Commerce, 

Springfield, VA 22161, PB-82-168279, description, 30 p., 

PB-82-1 68287, magnetic tape.

Turekian, K.K., 1977, Geochemical distribution of elements, in 

Encyclopedia of science and technology, 4th ed.: New 

York, McGraw-Hill, p. 627-630.

U.S. Bureau of Mines and U.S. Geological Survey, 1980, Principles of a resource/reserve classification for minerals: U.S. 

Geological Survey Circular 831, 5 p.

U.S. Geological Survey, 1972, Aeromagnetic map of part of the 

Lovelock, Reno, and Millet 1° by 2° quadrangles, Nevada: 

U.S. Geological Survey Open-File Report 72-386, scale 

1:250,000.

Western Geophysical Company of America, 1981, National 

gamma-ray spectrometer and magnetometer survey, Susanville quadrangle, California final report: U.S. Department 

of Energy Open-file Report GJBX-410 (81), v. 2,95 p., scale 

1:500,000.

A8 Mineral Resources of Wilderness Study Areas Northeastern California and Part of Adjacent Washoe County, Nevada
APPENDIXES

DEFINITION OF LEVELS OF MINERAL RESOURCE POTENTIAL 

AND CERTAINTY OF ASSESSMENT

Definitions of Mineral Resource Potential

LOW mineral resource potential is assigned to areas where geologic, geochemical, and geophysical 

characteristics define a geologic environment in which the existence of resources is permissive. This 

broad category embraces areas with dispersed but insignificantly mineralized rock as well as areas with 

few or no indications of having been mineralized.

MODERATE mineral resource potential is assigned to areas where geologic, geochemical, and geophysical 

characteristics indicate a geologic environment favorable for resource occurrence, where interpretations 

of data indicate reasonable likelihood of resource accumulation, and (or) where an application of 

mineral-deposit models indicates favorable ground for the specified type(s) of deposits.

HIGH mineral resource potential is assigned to areas where geologic, geochemical, and geophysical 

characteristics indicate a geologic environment favorable for resource occurence, where interpretations of 

data indicate a high degree of likelihood for resource accumulation, where data supports mineral-deposit 

models indicating presence of resources, and where evidence indicates that mineral concentration has 

taken place. Assignment of high resource potential to an area requires some positive knowledge that 

mineral-forming processes have been active in at least part of the area.

UNKNOWN mineral resource potential is assigned to areas where information is inadequate to assign low, 

moderate, or high levels of resource potential.

NO mineral resource potential is a category reserved for a specific type of resource in a well-defined area.

Levels of Certainty

t

(J 

cc

D 

O

U/A

UNKNOWN

POTENTIAL

H/B

HIGH POTENTIAL

M/B

MODERATE POTENTIAL

L/B

LOW

POTENTIAL

H/C

HIGH POTENTIAL

M/C

MODERATE POTENTIAL

L/C

LOW

POTENTIAL

H/D

HIGH POTENTIAL

M/D

MODERATE POTENTIAL

L/D

LOW POTENTIAL

N/D

NO POTENTIAL

B C 

LEVEL OF CERTAINTY

A. Available information is not adequate for determination of the level of mineral resource potential.

B. Available information suggests the level of mineral resource potential

C. Available information gives a good indication of the level of mineral resource potential.

D. Available information clearly defines the level of mineral resource potential.

Abstracted with minor modifications from:

Taylor, R. B., and Steven, T. A., 1983. Definition of mineral resource potential: Economic Geology,

v. 78, no. 6, p. 1268-1270. 

Taylor, R. B., Stoneman, R. J., and Marsh, S. P., 1984, An assessment of the mineral resource potential

of the San Isabel National Forest, south-central Colorado: U.S. Geological Survey Bulletin 1638, p.

Goudarzi, G H., compiler, 1984, Guide to preparation of mineral survey reports on public lands: U.S. 

Geological Survey Open-File Report 84-4)787, p 7, 8.

Mineral Resources of the Twin Peaks Wilderness Study Area, Washoe County, Nevada, and Lassen County, California A11
RESOURCE/RESERVE CLASSIFICATION

ECONOMIC

MARGINALLY 

ECONOMIC

SUBECONOMIC

IDENTIFIED

Demonstrated

Measured Indicated

I 

Reserves

I 

j_r^

Marginal 

Reserves

1

1

Demonstrated 

Subeconomic 

Resources

I

RESOURCES

Inferred

Inferred 

Reserves

Inferred 

Marginal 

Reserves

Inferred 

Subeconomic 

Resources

UNDISCOVERED RESOURCES

Probability Range

Hypothetical Speculative

1

1

1

Major elements of mineral resource classification, excluding reserve base and inferred reserve base. Modified from U.S. Bureau of Mines 

and U.S. Geological Survey, 1980, Principles of a resource/reserve classification for minerals: U.S. Geological Survey Circular 831, p. 5.

A12 Mineral Resources of Wilderness Study Areas Northeastern California and Part of Adjacent Washoe County, Nevada
GEOLOGIC TIME CHART 

Terms and boundary ages used by the U.S. Geological Survey in this report

EON

Phanerozoic

Proterozoic

Archean

ERA

Cenozoic

Mesozoic

Paleozoic

Late Proterozoic

Middle Proterozoic

Early Proterozoic

Late Archean

Middle Archean

Early Archean

PERIOD

Quaternary

Tertiary

Neogene 

Subperiod

Paleogene 

Subperiod

Cretaceous

Jurassic

Triassic

Permian

Carboniferous 

Periods

Pennsylvanian

Mississippian

Devonian

Silurian

Ordovician

Cambrian

pre- Archean 2

EPOCH

Holocene

Pleistocene

Pliocene

Miocene

Oligocene

Eocene

Paleocene

Late 

Early

Late 

Middle 

Early

Late 

Middle 

Early

Late 

Early

Late 

Middle 

Early

Late 

Early

Late 

Middle 

Early

Late 

Middle 

Early

Late 

Middle 

Early

Late 

Middle 

Early

AGE ESTIMATES 

OF BOUNDARIES 

(in Ma)

- 0.010

- 1.7

\j

f* jt - 24

«3O

- 55\J *J

 CC

- 96 

 npI«3O

one

- -240

> 290 ^&\J 

 ~330 11/*\

_ ocr\

u 410

 4*35 *TO«J

*- 500

 ~5701

*J / \J

- 900

- 1600

- 2500

- 3000

- 3400

'Rocks older than 570 Ma also called Precambrian, a time term without specific rank. 

Informal time term without specific rank.

Mineral Resources of the Twin Peaks Wilderness Study Area, Washoe County, Nevada, and Lassen County, California A13
GPO 585-045/78033