rr

Mineral Resources of the Upper Deep Creek 

Wilderness Study Area, 

Owyhee County, Idaho

U.S. GEOLOGICAL SURVEY BULLETIN 1719-G

Chapter G

Mineral Resources of the

Upper Deep Creek Wilderness Study Area,

Owyhee County, Idaho

By SCOTT A. MINOR, HARLEY D. KING, DOLORES M. KULIK, 

and DONALD L. SAWATZKY 

U.S. Geological Survey

DONALD O. CAPSTICK 

U.S. Bureau of Mines

U.S. GEOLOGICAL SURVEY BULLETIN 1719

MINERAL RESOURCES OF WILDERNESS STUDY AREAS: 

OWYHEE RIVER REGION, IDAHO AND NEVADA
DEPARTMENT OF THE INTERIOR 

DONALD PAUL MODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

UNITED STATES GOVERNMENT PRINTING OFFICE. WASHINGTON : 1987

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 Upper Deep Creek Wilderness 

Study Area, Owyhee County, Idaho.

U.S. Geological Survey Bulletin 1719-G

Bibliography

Supt. of Docs. No.: I 19.3:1719-G

1. Mines and mineral resources Idaho Upper Deep Creek

Wilderness. 2. Upper Deep Creek Wilderness (Idaho)

I. Minor, Scott A. II. Series.

QE75.B9 No. 1719-G 557.3s 

[TN24.I2] [5531 .09796'21]

87-600294
STUDIES RELATED TO WILDERNESS

Bureau of Land Management Wilderness Study Area

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 

Upper Deep Creek Wilderness Study Area (ID-111-044), Owyhee County, Idaho.

CONTENTS

Summary Gl

Abstract 1

Character and setting 1

Identified resources 1 

Mineral resource potential 1 

Introduction 3

Character and setting 3

Previous and present investigations 3 

Appraisal of identified resources 5

History and production 5

Mineral deposits 5 

Assessment of mineral resource potential 6

Geology 6

Geochemical studies 6

Geophysical studies 7

Mineral and energy resource potential 8

Previous and present investigations 8 

References cited 9 

Appendixes

Definition of levels of mineral resource potential and certainty of assessment 12

Resource/reserve classification 13

Geologic time chart 14

FIGURES

1. Index map showing location of Upper Deep Creek Wilderness Study Area, 

Owyhee County, Idaho G2

2. Map showing mineral resource potential and geology of Upper Deep Creek 

Wilderness Study Area, Owyhee County, Idaho 4

MINERAL RESOURCES OF WILDERNESS STUDY AREAS: 

OWYHEE RIVER REGION, IDAHO AND NEVADA

Mineral Resources of the

Upper Deep Creek Wilderness Study Area

Owyhee County? Idaho

By Scott A. Minor, Harley D. King, Dolores M. Kulik, 

and Donald L. Sawatzky 

U.S. Geological Survey

Donald O. Capstick 

U.S. Bureau of Mines

SUMMARY

Abstract

The Upper Deep Creek Wilderness Study Area 

(ID-111-044) is located on the northern Owyhee 

Plateau in southwest Idaho and encompasses 11,510 

acres, of which the U.S. Geological Survey and the 

U.S. Bureau of Mines were asked to study 5,700 

acres. Hereafter, the terms "study area" and 

"wilderness study area" refer pnly to the smaller 

acreage. Field work for this report was conducted in 

1985 to assess the identified mineral resources (known) 

and mineral resource potential (undiscovered) of the 

area. No mines, prospects, or claims are located in 

the study area and there are no identified mineral or 

energy resources. The study area has moderate 

resource potential for small gold placers and low 

potential for gold and silver resources in epithermal 

(hydrothermal) deposits. The study area also has low 

potential for tin and uranium resources; the southern 

part has low potential for diatomite resources. The 

potential for oil, gas, and geothermal energy resources 

in the study area is low.

Character and Setting

The Upper Deep Creek Wilderness Study Area is 

located on the northern Owyhee Plateau of southwest 

Idaho (fig. 1), about 80 mi southwest of Boise. The 

terrain is characterized by a stream-dissected plateau, 

averaging about 5,300 ft in elevation, with several 

prominent canyons, including the 200- to 400-ft-deep 

canyon of Deep Creek that extends the length of the 

study area. The surrounding Owyhee Plateau is

underlain by a thick (greater than 800 ft) flat-lying 

sequence of Miocene (see appendix for geologic time 

chart) rhyolitic ash-flow tuffs, basalt flows, and minor 

interbedded sedimentary rocks. A thick rhyolitic ashflow tuff is exposed in most of the study area; the tuff 

is overlain in the southern part by a sequence of thin 

basalt flows and basal sedimentary rocks (fig. 2). 

Geologic and geophysical data indicate that the study 

area lies within a large collapsed caldera. The ashflow tuff and overlying units are interpreted to be part 

of a post-collapse sequence that has filled and buried 

most of the caldera. A small (0.5 by 0.25 mi) basalt 

maar crater (Indian Lake, fig. 2) is located directly 

east of the study area.

Identified Resources

No mining claims were located and no minerals 

were produced in the study area. There are no 

identified mineral or energy resources within the study 

area.

Mineral Resource Potential

There is moderate resource potential for placer 

gold resources obtained by recreational, suctiondredge methods along the Deep Creek stream bed 

(fig. 2); relatively high concentrations of particulate 

gold were identified in sand and gravel bars along the 

creek within the study area.

The entire study area has a low potential for gold 

and silver resources in epithermal deposits (fig. 2). 

This is indicated by weak, sporadic geochemical 

anomalies, and the presence of placer gold. Altered

G1
11 7 00'

42"'45'

42°15' 

APPROXIMATE BOUNDARY

WILDERNESS STUDY AREA

Figure 1. Index map showing location of Upper Deep Creek Wilderness Study Area, Owyhee County, Idaho.

G2
rock is generally lacking, and any occurrences of 

precious metals in near-surface rocks are probably 

insignificant.

There is low potential for tin resources in the 

rhyolitic tuff underlying the study area. A tin-bearing 

mineral identified in heavy-mineral-concentrate 

samples suggests the possible presence.of rhyolitehosted tin deposits, but many of the common 

attributes of this type of deposit are lacking.

The potential for uranium resources is low 

throughout the study area. Several weak uranium and 

thorium geochemical anomalies were detected but no 

minerals bearing these elements other than zircon, 

which may contain thorium, were observed. The 

elemental anomalies are believed to reflect relatively 

high background values of uranium and thorium within 

the rhyolitic ash-flow tuff.

No diatomite was identified within the limited 

exposures of sedimentary rock in the study area. The 

depositional environment of the sedimentary rocks 

may have been favorable for the formation of only 

small-volume, discontinuous diatomite deposits. The 

diatomite resource potential is therefore assessed as 

low for areas underlain by sedimentary rock in the 

southern part of the study area.

Hydrocarbon source and reservoir rocks are not 

present in the study area, and there are no active oil 

and gas leases nor producing wells in the area. It is 

unknown, but doubtful, if hydrocarbon source or 

reservoir rocks are present at depth beneath the study 

area; therefore, the potential for oil and gas resources 

is low. Similarly, the potential for geothermal 

resources is assessed as low; no recent volcanic rocks, 

hot springs, or geothermal wells exist in the area 

despite probable high regional heat flow.

INTRODUCTION

This mineral survey was requested by the U.S. 

Bureau of Land Managment and is a joint effort by the 

U.S. Geological Survey and the U.S. Bureau of Mines. 

The U.S. Bureau of Mines 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 U.S. Geological Survey 

are designed to provide a reasonable scientific basis 

for assessing the potential for undiscovered mineral 

resources by determining geologic units and structures, 

possible environments of 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 

appendix for the definition of levels of mineral 

resource potential, certainty of assessment, and 

classification of identified resources.

Character and Setting

The Upper Deep Creek Wilderness Study Area is 

located about 35 mi southeast of Jordan Valley, Oreg.,

and 80 mi southwest of Boise on the northern Owyhee 

Plateau of southwest Idaho (fig. 1). The U.S. Bureau of 

Land Management requested studies on a total of 5,700 

acres of the 11,510-acre Upper Deep Creek Wilderness 

Study Area. Other wilderness study areas in the region 

include the North Fork Owyhee River (ID-016-040) 

(Minor and others, 1986) and Deep Creek-Owyhee 

River (ID-016-049A) (Sawlan and others, 1987) 

Wilderness Study Areas located about 3 mi northwest 

and southeast of the study area, respectively.

Elevations in the Upper Deep Creek Wilderness 

Study Area range from about 5,770 ft along the north 

boundary to 4,800 ft where Deep Creek crosses the 

south boundary. The rugged, extensively streamdissected northern part of the study area contrasts 

sharply with the curving, table-rimmed Deep Creek 

canyon of the southern part (fig. 2). The 200- to 400- 

ft-deep, steeply walled canyon cut by south-flowing 

Deep Creek dominates the study-area landscape. The 

surrounding Owyhee Plateau region is characterized by 

flat-lying to gently rolling tablelands locally incised by 

tributary streams of the Owyhee River such as Deep 

Creek (fig. 1). Most of the streams are intermittent, 

reflecting the semiarid climate of the region. Juniper 

trees, low-lying sage and other brush, and seasonal 

varieties of grasses and wildflowers grow throughout 

most of the study area. The larger stream channels 

support a variety of riparian vegetation.

An improved county-maintained gravel road that 

extends from Jordan Valley, Oreg., to Grand View, 

Idaho, passes within 2 mi of the northern edge of the 

study area and provides the best access (fig. 1). 

Several less-used gravel roads and jeep trails branching 

off this road extend south to or near the study area.

Previous and Present Investigations

The earliest published geologic map of the 

region, which covers the northern part of the study 

area, was a reconnaissance map (scale 1:62,500) 

accompanying a report by Bennett (1976) on the 

geology and geochemistry of the South MountainJuniper Mountain area. The only geologic map 

covering the entire study area is that of western 

Owyhee County (scale 1:125,000) by Ekren and others 

(1981) . Other geologic studies related to the study 

area have addressed the rhyolite ash-flow tuffs (Ekren 

and others, 1984) and stratigraphy (Ekren and others, 

1982) of the region.

The U.S. Bureau of Land Management conducted 

a preliminary mineral survey of lands proposed for 

wilderness study areas in the region, including the 

Upper Deek Creek Wilderness Study Area (Gloria 

Derby, unpub. data, 1981). Geochemical (Oak Ridge 

Gaseous Diffusion Plant, 1982; Berry and others, 1982) 

and geophysical (Geodata International, Inc., 1979) 

surveys were conducted for the U.S. Department of 

Energy's National Uranium Resource Evaluation 

(NURE) program to assess the radioactive mineral 

potential of the region. A geology, energy, and 

mineral (GEM) resources report was prepared by 

Mathews and Blackburn (1982) for the Pole Creek GEM 

Resource Area, which includes the Upper Deep Creek 

Wilderness Study Area.

The U.S. Geological Survey conducted field 

investigations in the study area in the summer of

G3
116°40'

42°32'30"

42°30'

42°27'30"

Tb

L/C Sn, U, Geo

L/B Au, Ag, [1], O, G 

(entire study area)

Dia

southern part 

study are

Tb

APPROXIMATE BOUNDARY

OF

UPPER DEEP CREEK

WILDERNESS STUDY AREA

(ID-111-044)

Tb

Qal

Figure 2 . Mineral resource potential and geology of Upper Deep Creek Wilderness Study 

Area, Owyhee County, Idaho. Geology modified from Ekren and others (1981).

G4
. .jfVg£7W

EXPLANATION

Area with moderate mineral resource potential 

Area with low mineral resource potential

APPRAISAL OF IDENTIFIED RESOURCES

 « By Donald O. Capstick 

'-.- ': U.S. Bureau of Mines

See appendix for definition of mineral resource potential and ^ 

certainty of assessment

-' ' Commodities

Au Gold

- Afl ,.j . Silver

 Sw? ' .. Tin / -; t

U' Uranium

Dia Diatomite J

O,G Oil and Gas

Geo Geothermal energy

, - . - Deposit types

{

1J Epithermal vein and dissemination 

2] Placer

Geologic map units 

Qal Alluvium (Quaternary) 

Qls Landslide (Quaternary) 

Tb Banbury Basalt and unnamed interbedded

sedimentary rocks (Miocene) 

Rocks of Juniper Mountain volcanic center

(Miocene)-ln this area, consist of: 

Tp Tuff of Juniper Mountain (equivalent to

lower lobes of Ekren and others, 1981) 

Tjs Swisher Mountain Tuff

 Contact-Dashed where approximately located 

Maar crater

Figure 2. Continued.

1985. The studies included checking of existing 

geologic maps, local supplementary mapping, and 

geochemical sampling. Linear features that appear in 

Landsat multispectral-scanner images of the region 

were mapped and interpreted. Gravity data were 

acquired, processed, and compiled to supplement 

preexisting gravity and aeromagnetic data. 

Geochemical analyses were obtained for 11 streamsediment and nonmagnetic heavy-mineral-concentrate 

samples and 17 rock samples collected in the study 

area.

U.S. Bureau of Mines personnel conducted a 

library search of county, state, and U.S. Bureau of 

Land Management mining and mineral-lease records 

and U.S. Bureau of Mines production records for 

information on mines, prospects, and claims within the 

study area. Field work was conducted in 1985, which 

included a ground and air reconnaissance undertaken to 

search for evidence of undocumented prospecting 

activity. Three alluvial (placer) samples were 

collected to help evaluate any possible placer-gold 

resources. The results of work by the U.S. Bureau of 

Mines were reported by Capstick (1986). Detailed 

information is availible from the U.S. Bureau of Mines, 

Western Field Operations Center, E. 360 Third Avenue, 

Spokane, WA 99202.

History and Production

No mining claims have been located in the Upper 

Deep Creek Wilderness Study Area, and no minerals 

have been produced. A few tons of diatomite were 

extracted from a large diatomite deposit (Staley, 1964) 

about 5 mi southeast of the study area (fig. 1), but 

apparently there was no production since the 1930's 

(Powers, 1947; Capstick and Buehler, 1985). The Silver 

City mining district, about 35 mi north of the study 

area, has been active since 1863. Early gold and silver 

production in the district, from 1863 to about 1914, 

was valued at more than $40 million (Rodgers and 

others, 1980) from underground and placer mines. In 

1977, the Delamar mine was reopened as an open-pit, 

large-tonnage, low-grade disseminated silver and gold 

mine. Output in 1985 was valued at about $20 million 

(Nerco, Inc., 1985). The silver and gold are in Miocene 

rhyolite-hosted epithermal deposits.

Mineral Deposits

No identified mineral resources were delineated 

within the study area. Gold, however, was found in 

three samples collected from sand and gravel bars 

along Deep Creek (Capstick, 1986); gold 

concentrations are 0.00052, 0.00054, and 0.0068 trov 

ounces/yd 3 with values of $0.21, $0.22, and $2.72/yd y, 

respectively (at $400/troy ounce). These values are 

distinctly higher than the $0.02/yd average typical of 

the Owyhee canyonland and drainages (Gabby and 

Mayerle, 1985). However, the volume of the sand and 

gravel deposits is insufficient to be minable by largevolume commercial methods. Such methods require 

average gold values of several dollars per cubic yard 

and several thousand cubic yards of gravel to be 

treated per day. Commonly, the size and number of 

individual gold particles may increase dramatically in 

material on or near bedrock, raising the values 

substantially. Consequently, the area may be 

attractive for recreational or small-scale commercial 

suction-dredge operations.

Available evidence suggests that the gold came 

from a nearby source; the gold is bright, indicating it 

may have recently been liberated from the host rock, 

and the surface of the individual gold particles is 

angular rather than rounded, indicating they had 

traveled only a short distance. The area drained by 

Deep Creek northwest of the study area, to within 4 

mi of the boundary, was examined previously by the 

U.S. Bureau of Mines as part of their study of the 

North Fork Owyhee River Wilderness Study Area 

(Leszcykowski, 1986), and no gold was found. 

Therefore, the gold source may lie between the North 

Fork Owyhee River and Upper Deep Creek Wilderness 

Study Areas or within the northeastern part of the 

Upper Deep Creek Wilderness Study Area.

Blocky basalt forming the tables and canyon rims 

in the southern part of the study area (Banbury Basalt,

G5
fig. 2) may be suitable for use as dimension stone. 

Sand and gravel deposits (alluvium) usable for 

construction are also present in the study area. 

However, other higher quality, more accessible 

deposits of these commodities exist closer to 

markets. Basalt and sand and gravel do not constitute 

resources within the study area.

No jasper and only local, minor amounts of 

chalcedony and common opal(?) were noted in 

outcrops, although the geologic environment of the 

study area is similar to that of nearby wilderness study 

areas where these minerals are present in greater 

abundance (Capstick and Buehler, 1985; Gabby and 

Mayerle, 1985). There are no resource accumulations 

of these or other gem minerals in the study area.

ASSESSMENT OF MINERAL RESOURCE POTENTIAL

By Scott A. Minor, Harley D. King, Dolores M. Kulik, 

and Donald L. Sawatzky 

U.S. Geological Survey

Geology

The Upper Deep Creek Wilderness Study Area 

lies within the Owyhee volcanic field of Panze (1975), 

which consists of a thick pile of complexly 

interfingering and overlapping Tertiary volcanic, 

pyroclastic, and subordinate sedimentary rocks. 

Basement rocks, consisting of Mesozoic intrusive and 

metamorphic units, crop out within the Owyhee 

Mountains north of the study area. Rocks of the 

volcanic field are locally displaced along normal faults 

trending primarily north-northwest.

The study area is underlain by flat-lying, middle 

and upper Miocene rhyolitic ash-flow tuff, basalt 

flows, and minor intercalated sedimentary rocks (fig. 

2). The oldest rock unit is the tuff of Juniper 

Mountain (equivalent to the lower lobes of Juniper 

Mountain of Ekren and others, 1981), a subunit of the 

rocks of Juniper Mountain volcanic center (Ekren and 

others, 1981). The tuff of Juniper Mountain, which 

underlies most of the study area (fig. 2), is a rhyolitic 

ash-flow tuff made up of several cooling units. It has 

a minimum thickness of about 400 ft within the study 

area; its base is not exposed. The tuff typically 

contains more than 20 percent phenocrysts of quartz, 

plagioclase, potassium feldspar, and pyroxene. The 

gray, cryptocrystalline groundmass of the tuff 

weathers reddish to orangish brown. Flow foliations 

are ubiquitous and usually characterized by folds that 

have amplitudes as great as 300 ft. The tuff is 

characterized by outcrops that form jagged pinnacles 

and precipitous cliffs along the major drainages. The 

tuff apparently erupted from Juniper Mountain, a 

broad dome-shaped landform located 10 mi southwest 

of the study area (fig. 1) (Ekren and others, 1981 and 

1984),

A geologic reconnaissance of the region 

indicated that the study area is within a caldera (Minor 

and others, 1986), the north margin of which is exposed 

about 22 mi north of the study area. (The caldera is 

also expressed by gravity data collected in the region 

see Geophysical Studies section.) Eruption of the

Swisher Mountain Tuff, the oldest subunit of the rocks 

of Juniper Mountain volcanic center and exposed about 

3 mi north of the study area (Ekren and others, 1981), 

is inferred to have resulted in collapse of the caldera. 

Overlying rocks related to the Juniper Mountain 

volcanic center, including the tuff of Juniper 

Mountain, appear to be intracaldera tuffs that are 

possibly comagmatic with the Swisher Mountain Tuff. 

The younger tuffs and other overlying rocks overlap 

and conceal the caldera margin east, west, and south 

of the study area.

In the southern part of the study area, the tuff is 

overlain by flat-lying basalt flows and local basal 

sedimentary rocks mapped collectively by Ekren and 

others (1981) as "Banbury Basalt and unnamed 

interbedded sediments" (fig. 2). The basalt flows form 

mesas, including Little Point and Castro and Black 

Tables (fig. 2), that rim Deep Creek canyon in the 

southern part of the study area. The flows range from 

25 to 50 ft in thickness and have a maximum 

cumulative thickness of about 350 ft at the south end 

of the study area. Tabular upper parts of the flows 

commonly possess vesicles that are locally lined with 

calcite, clay, and (or) zeolite minerals. The basalts 

are aphyric to sparsely porphyritic; phenocrysts consist 

of olivine and (or) plagioclase, as well as less abundant 

iron oxides and pyroxene. The basal sedimentary 

rocks, which are usually concealed by basalt talus, 

have a maximum thickness of about 100 ft. They 

consist primarily of variegated vitric-ash tuff and 

fluvial and lacustrine tuffaceous sandstone and 

siltstone.

Small amounts of Quaternary alluvium are 

present along the major stream channels and consist of 

unconsolidated silt, sand, and gravel.

The study area lacks any faults with noticeable 

displacement. However, a zone of closely spaced, 

north-northwest-trending normal faults that cut rocks, 

of the Swisher Mountain Tuff and Banbury Basalt is 

present about 3 mi to the northeast (Ekren and others, 

1981). Indian Lake, an elliptical topographic 

depression (0.5 mi by 0.25 mi) located 0.5 mi east of 

the study area (fig. 2), was mapped by Ekren and 

others (1981) as a basalt maar. A maar is a crater 

having a low rim that forms principally by the violent 

explosion of steam derived from groundwater (Fisher 

and Schmincke, 1984).

Geochemical Studies

The reconnaissance geochemical study of the 

Upper Deep Creek Wilderness Study Area included the 

collection and analysis of 11 stream-sediment samples, 

11 nonmagnetic heavy-mineral-concentrate samples, 

and 17 rock samples.

All samples were analyzed semiquantitatively 

using direct-current arc emission spectrographic 

methods; rock and stream-sediment samples were 

analyzed by the method described by Crock and others 

(1987) and nonmagnetic heavy-mineral concentrates by 

the method described by Grimes and Marranzino 

(1968). Certain elements of interest in terms of 

resource potential or which have high lower limits of 

determination by emission spectrography were also 

analyzed by other more precise methods; antimony,

G6
arsenic, bismuth, cadmium, and zinc were analyzed by 

inductively coupled argon plasma-atomic emission 

spectroscopy and gold and mercury were analyzed by 

atomic absorption (methods described in Crock and 

others, 1987). A split of each of the heavy-mineralconcentrate samples was examined with a binocular 

microscope for ore- and ore-related minerals. The 

analytical data are by M.S. Erickson and others 

(Unpublished data, 1986).

Anomalous values were determined primarily by 

considering the range, distribution, and mean of the 

elemental concentrations. Average elemental crustal 

abundances and high background values expected for 

certain rock types were also considered.

A stream-sediment sample collected in the 

northeast part of the study area along Slack Creek 

(fig. 2) contains 1.4 parts per million (ppm) mercury. 

No other notably anomalous values were detected in 

stream-sediment samples from the study area.

Bennett (1976) reported anomalous silver 

concentrations of 3.2 and 0.99 ppm in two streamsediment samples collected along one of the Slack 

Creek tributaries in the study area. However, no 

anomalous metal values were reported for his 

remaining 10 samples collected in the northern part of 

the study area. Furthermore, no anomalous silver 

concentrations were detected during the present study 

in samples collected in this area. The sporadic, weak 

nature of the metal anomalies reported by Bennett 

(1976) and in this study indicate that there are no 

significant deposits of these or related elements near 

the surface.

Anomalously high concentrations of thorium and 

tin were detected in some of the heavy-mineralconcentrate samples collected in the study area. 

Three samples from the northern part of the study 

area contain anomalous concentrations of thorium 

(200-300 ppm). These samples were determined, by 

microscopic examination, to be composed 

predominantly of zircon, which can contain thorium. 

Other thorium-bearing minerals, such as thorite, were 

not noted. The values are considered to be too low to 

indicate a thorium-ore deposit, however, the element 

is of interest as a possible indicator of uranium. Only 

slightly anomalous concentrations (4.0-6.6 ppm) of 

uranium were detected in 4 out of 10 stream-sediment 

samples collected near the study area as part of the 

NURE assessment of the region (Oak Ridge Gaseous 

Diffusion Plant, 1982). NURE investigators concluded 

that rocks underlying the region are unfavorable for 

uranium deposits (Berry and others, 1982).

Tin is present in anomalous concentrations (1,500 

and greater than 2,000 ppm) in two heavy-mineralconcentrate samples from the central and southern 

parts of the study area. Cassiterite variety wood tin, 

a common tin-bearing mineral, was identified by 

microscopic examination in the mineralogy splits of 

those \samples. A rhyolite-hosted tin deposit is 

suggested by the occurrence of this variety of 

cassiterite and the predominance of welded rhyolitic 

tuff in the area (Boyle, 1974; Cox and Singer, 1986). 

Most of the characteristics described for this type of 

deposit, however, are lacking in the study area. The 

rhyolitic ash-flow tuffs underlying much of the 

Owyhee Plateau (see Ekren and others, 1981), including 

the tuff of Juniper Mountain, are probably of

peralkalic chemistry (J.J. Rytuba, oral commun., 

1986). Peralkalic rhyolites are commonly enriched in 

lithophile elements, including tin (MacDonald and 

Bailey, 1973), suggesting that the primary source of 

the tin is the lower lobes of Juniper Mountain.

No anomalous elemental concentrations are 

present in the 17 rock samples collected in the study 

area, with the exception of an 18-ppm arsenic value 

detected in a sample from Deep Creek canyon east of 

Black Table (fig. 2). The anomalous sample was taken 

from a local (approximately 0.25 mi ) alteration zone 

within the tuff of Juniper Mountain. Two other rock 

samples from the same altered zone lack any 

anomalous concentrations. The high arsenic value may 

be associated with relatively high primary arsenic 

concentrations within the tuff of Juniper Mountain, or 

alternatively may be reflecting mineralized rock at 

depth.

Geophysical Studies

Geophysical data provide information on the 

subsurface distribution of rock masses and the 

structural framework of the region. Gravity and 

aeromagnetic studies were undertaken as part of the 

mineral resource evaluation of the study area.

Gravity data were obtained from files 

maintained by the Defense Mapping Agency of the U.S. 

Department of Defense and supplemented by 

additional field data obtained by the U.S. Geological 

Survey in 1985. Bouguer gravity anomaly values were 

computed using the 1967 gravity formula (International 

Association of Geodesy, 1967) and a reduction density 

of 2.67 g/cm (grams per cubic centimeter). Terrain 

corrections were made by computer for a distance of 

104 mi from the station using the method of Plouff 

(1977).

The area of extreme southwestern Idaho is 

characterized by intermediate Bouguer values of 

between -150 and -175 milligals (mGal) over a terrane 

underlain predominantly by rhyolitic rocks. Gravity 

values decrease to the south where the rhyolites 

become thicker and increase to the north where 

Cretaceous intrusive rocks crop out in the Owyhee 

Mountains. In the Owyhee Plateau region a roughly 

circular, low gravity anomaly 50 to 55 mi in diameter 

suggests an underlying volcano-tectonic depression or 

caldera that may have been a source of the ash-flow 

tuffs of the Juniper Mountain volcanic center (see 

Geology section). A 5- to 10-mGal gravity high 

superimposed on the west half of the extensive gravity 

low overlaps the southern part of the study area and 

may represent a caldera-related resurgent dome.

Aeromagnetic data evaluated in this report are 

from the aeromagnetic map of Idaho (U.S. Geological 

Survey, 1978). Flightlines were flown east-west at 5- 

mi spacing and 12,500 ft barometric elevation.

The aeromagnetic values show only moderate 

(approximately 300 gammas) variation over 

southwesternmost Idaho except in an area 30 mi 

northeast of the study area. There values increase to 

1,400 gammas over a buried, highly magnetic mass 

that extends southeastward to the border between 

Idaho and Utah. This anomaly is well separated from 

the study area and was not evaluated for this report.

G7
An aerial gamma-ray survey was performed in 

the region as part of the NURE program (Geodata 

International, Inc., 1979). Three east-west composite 

flightlines spaced at intervals of 3 mi traversed the 

study area. Values of equivalent uranium for rocks in 

the area determined from the aerial survey indicate 

that the tuff of Juniper Mountain has comparatively 

high background levels.

Linear features in Landsat multispectral-scanner 

(MSS) images were mapped by photogeologic 

interpretation for the region of southwestern Idaho. 

Linear features are the surface expression of rock 

fracture patterns and other structural and lithologic 

lineaments. Analysis of linear features, in conjunction 

with other geologic and geophysical data, are used to 

help define relations such as structural control of 

mineralization.

Generally few linear features are seen in the 

MSS images of the volcanic rocks of southwestern 

Idaho. However, two sets of linear features with 

dominant N. 20° W. and N. 60-80° E. trends are 

present in an area bounded by long 116°-117° W. and 

lat 42°30'-430 N., which includes the northern part of 

the study area. Maximum concentrations lie in an 

elongate zone trending N. 20° W., with the N. 20° W. 

trend prominent at the south end of the zone near the 

study area and the N. 80° E. trend prevalent at the 

north end. The dominant north-northwest trend is 

similar to that of major fault zones trending N. 20° W. 

and N. 40° W. that lie northeast of the study area. 

The east-northeast trend may be related to a pervasive 

regional-fracture set found in other linear-feature 

investigations in the region (for example, Rowan and 

Purdy, 1984) that proved to be an important structural 

control of mineralization.

Mineral and Energy Resource Potential

Trace-element signatures detected in rock and 

stream-sediment samples collected within the Upper 

Deep Creek Wilderness Study Area may reflect, in 

part, relatively high primary background 

concentrations of these elements in the tuff of Juniper 

Mountain exposed in most of the study area. 

Alternatively, the anomalies could be expressions of 

leakage halos related to mineralized rocks at depth. 

Anomalous concentrations of certain metals, such as 

those of arsenic, mercury, and silver detected in the 

study area, are commonly associated with auriferous 

mineral deposits (Boyle, 1974; Cox and Singer, 1986). 

Significant gold values were found in three placer 

samples collected along Deep Creek in the study 

area. The gold most likely was derived from goldmineralized rocks upstream just northeast of the study 

area. One small zone of possible hydrothermal 

alteration was identified; the zone is characterized by 

silicified, argillically altered, bleached, and limonitestained tuff; minor chalcedony and opal(?) line cavity 

walls within the zone. A slightly anomalous 

concentration of arsenic was detected in one of three 

rock samples from the altered zone. The sporadic and 

weak nature of the stream-sediment- and rock-sample 

. metalliferous anomalies in the study area and the 

general lack of alteration suggest that any possible 

mineralized rocks are at some unknown depth. The

numerous small fractures and joints that cut the 

rhyolitic ash-flow tuff would provide conduits for 

leakage of hydrothermal metal-rich solutions from 

below. The small alteration zone described above may 

have formed along one such conduit. Mineralization, if 

any, probably resulted from hydrothermal activity 

associated with caldera magmatism that occurred in 

the region in middle Miocene time, in a similar fashion 

to that postulated for the Delamar silver-gold 

mineralization (Halsor, 1983) in the Silver City mining 

district.

The cause(s) of the anomalous metal concentrations in the study area is conjectural due to the 

sparsity of alteration and mineral occurrences and the 

lack of deposits. There is little likelihood for 

discovery of gold and silver deposits other than, 

perhaps, placer gold obtained by recreational suctiondredging methods. Any mineralized rocks are 

concealed by an unknown thickness of volcanic and 

pyroclastic rocks. There is moderate potential, 

certainty level C, for small-volume placer gold along 

Deep Creek; the entire study area has a low potential, 

certainty level B, for gold and silver resources in 

epithermal mineral deposits (fig. 2).

The presence of the tin-bearing mineral 

cassiterite variety wood tin in two heavy-mineralconcentrate samples partly derived from rhyolitic 

welded ash-flow tuff in the study area indicates there 

is some possibility for the occurrence of tin 

resources. The common attributes of tin deposits in 

rhyolite flows cassiterite-rich disseminations, veins, 

and veinlets within fractured and brecciated host rock 

(Cox and Singer, 1986) were not observed in the study 

area. The tuff of Juniper Mountain (fig. 2) is a likely 

source of the tin; the tuff's apparent peralkalic 

chemistry is usually associated with high background 

values of tin. Such primary tin within the tuff is 

probably highly disseminated and is unlikely to be 

economically significant. The potential for tin 

resources in the study area is considered to be low 

with a C certainty level (fig. 2) because the geologic 

environment is not favorable for concentrations of tin 

minerals.

There is little likelihood for uranium resources in 

the study area. No uranium-bearing mineral 

occurrences or hydrothermal alteration assemblages 

commonly associated with volcanic-hosted uranium 

deposits were identified. Several weak thorium and 

uranium geochemical anomalies detected in and near 

the study area probably reflect the relatively high 

equivalent-uranium background values determined by 

aerial survey (Geodata International, Inc., 1979) for 

the rhyolitic tuff unit. The study area is thus judged 

to have low potential, certainty level C, for uranium 

resources (fig. 2).

Lacustrine sedimentary rocks formed in a 

geologic environment favorable for the accumulation 

of diatomite are locally exposed along the base of the 

Banbury Basalt in the southern part of the study area 

(fig. 2). Large, relatively high-grade diatomite 

deposits mined 5 mi southeast of the study area (fig. 1) 

(Staley, 1964) are contained in lacustrine strata 

essentially correlative with the sedimentary rocks, 

although the deposits apparently pinch out and do not 

extend into the study area. The sedimentary rocks in 

the study area are largely concealed by several

G8
hundred feet of basalt overburden and, along the 

canyon walls, by basalt talus. No diatomite was 

identified in the few exposures of the unit and any 

undiscovered deposits would most likely be thin and 

discontinuous. There is low potential for diatomite 

resources in the southern part of the study area, 

certainty level B (fig. 2).

Available geologic data do not indicate the 

presence of oil and gas resources in or near the study 

area. The Owyhee Plateau is underlain by at least 

1,000 ft of Tertiary volcanic and pyroclastic rocks 

(Ekren and others, 1981) that are not likely sources or 

reservoirs of hydrocarbons. The nearest Tertiary 

sedimentary rocks that are possible hydrocarbon 

sources are in the Sucker Creek Formation (Warner, 

1980) and are located 32 mi northwest of the study 

area. These rocks were probably deposited in localized 

basins that do not extend into the study area. It is not 

known if significant amounts of sedimentary rocks 

older than those that crop out exist at depth under the 

study area. The localized sedimentary rocks at the 

base of the Banbury Basalt lack surficial tar and oil 

seeps, black shales, or other evidence of 

hydrocarbons. The nearest exposed pre-Tertiary 

basement rocks, about 15 mi northwest of the study 

area (Ekren and others, 1981), consist of metamorphic 

and intrusive rocks also unlikely hydrocarbon sources 

or reservoirs.

In assessing the petroleum potential of 

wilderness lands in Idaho, Sandberg (1983) determined 

that the study area has "low potential" for yielding oil 

or gas. At present, there are no active oil and gas 

leases nor producing wells in the study area and 

surroundings. In consideration of the unfavorable, 

although somewhat limited, geologic evidence 

regarding the presence of hydrocarbon source and 

reservoir rocks and the lack of oil and gas leases, 

exploration, and production, the study area is judged to 

have low potential, certainty level B, for oil and gas 

resources (fig. 2).

Strong indications of geothermal activity, such 

as hot springs, sulfurous odors, and recent volcanism, 

are lacking in the study area. A list of thermal springs 

and wells in Idaho compiled by Bliss (1983) did not 

include any such features in the study area region. In 

an evaluation of geothermal resources of southern 

Idaho, Mabey (1983) noted that the regional heat flow 

in the Owyhee Plateau area is probably high, and 

favorable structures for hydrothermal convection 

likely exist there. However, he did not identify any 

geothermal systems in or near the study area. The 

potential for geothermal resources in the study area is 

low, certainty level C, because direct evidence of 

these resources is lacking.

REFERENCES CITED

Beikman, H.M., Hinkle, M.E., Frieders, Twila, Marcus, 

S.M., and Edward, J.R., 1983, Mineral surveys by 

the Geological Survey and the Bureau of Mines of 

Bureau of Land Management Wilderness Study 

Areas: U.S. Geological Survey Circular 901, 28

PBennett, E.H., 1976, Reconnaissance geology and 

geochemistry of the South Mountain-Juniper

Mountain region, Owyhee County, Idaho: Idaho 

Bureau of Mines and Geology Pamphlet 166, 68 p.

Berry, M.R., Castor, S.B., and Robins, J.W., 1982, 

National uranium resources evaluation, Jordan 

Valley quadrangle, Oregon and Idaho: United 

States Department of Energy Open-File Report ( 

PGJ/F-132(82), 33 p. (Available through U.S. 

Geological Survey Branch of Open-File Services, 

Box 25425, Federal Center, Denver, Colo., 

80225.)

Bliss, J.D., 1983, Idaho: Basic data for thermal springs 

and wells as recorded in Geotherm, part A: U.S. 

Geological Survey Open-File Report 83-431 A, 63

PBoyle, R.W., 1974, Elemental associations in mineral 

deposits and indicator elements of interest in 

geochemical prospecting (revised): Geological 

Survey of Canada Paper 74-45, 40 p. 

Capstick, D.O., 1986, Mineral resources of the Upper 

Deep Creek study area, Owyhee County, Idaho: 

U.S. Bureau of Mines Open-File Report MLA 

73-86, 10 p.

Capstick, D.O., and Buehler, A.R., 1985, Mineral 

resources of the Deep Creek-Owyhee River study 

area, Owyhee County, Idaho: U.S. Bureau of 

Mines Open-File Report MLA 54-85, 14 p. 

Cox, D.P., and Singer, D.A., eds., 1986, Mineral 

deposit models: U.S. Geological Survey Bulletin 

1693, 379 p.

Crock, J.G., Briggs, P.H., Jackson, L.L., and Lichte, 

F.E., 1987, Analytical methods for the analysis 

of stream sediments and rocks from wilderness 

study areas: U.S. Geological Survey Open-File 

Report 87-84, 35 p.

Ekren, E.B., Mclntyre, D.H., and Bennett, E.H., 1984, 

High-temperature, large-volume, lava-like ashflow tuffs without calderas in southwestern 

Idaho: U.S. Geological Survey Professional Paper 

1272, 76 p.

Ekren, E.B., Mclntyre, D.H., Bennett, E.H., and Malde, 

H.E., 1981, Geologic map of Owhyee County, 

Idaho west of longitude 116° W.: U.S. Geological 

Survey Miscellaneous Series Investigations Map I1256, scale 1:125,000.

Ekren, E.B., Mclntyre, D.H., Bennett, E.H., and 

Marvin, R.F., 1982, Cenozoic stratigraphy of 

western Owyhee County, Idaho, in Bonnischen, 

Bill and Breckenridge, R.M., eds., Cenozoic 

geology of Idaho: Idaho Bureau of Mines and 

Geology Bulletin 26, p. 215-235. 

Fisher, R.V., and Schmincke, H.-U., 1984, Pyroclastic

rocks: Berlin, Springer-Verlag, 472 p. 

Gabby, P.N., and Mayerle, R.T., 1985, Mineral 

resources of the Owyhee River Canyon 

Wilderness Study Area, Owyhee County, Idaho: 

U.S. Bureau of Mines Open-File Report MLA 68- 

85, 15 p.

Geodata International, Inc., 1979, Aerial radiometric 

and magnetic survey, Jordan Valley national 

topographic map, Oregon and Idaho: United 

States Department of Energy Open-File Report 

GJBX-95(80), 203 p., 108 fiche. (Available 

through U.S. Geological Survey Branch of OpenFile Services, Box 25425, Federal Center, 

Denver, Colo., 80225.) 

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

G9
survey reports on public lands: U.S. Geological 

Survey Open-File Report 84-787, 51 p.

Grimes, D.J., and Marranzino, A.P., 1968, Directcurrent arc and alternating-current spark 

emmission spectrographic field methods for the 

semiquantitative analysis of geologic materials: 

U.S. Geological Survey Circular 591, 6 p.

Halsor, Sid, 1983, A volcanic dome complex and 

genetically associated hydrothermal system, 

Delamar silver mine, Owyhee County, Idaho: 

Houghton, Mich., Michigan Technological 

University, M.S. thesis, HI p.

International Association of Geodesy, 1967, Geodetic 

Reference System, 1967: International 

Association of Geodesy Special Publication No. 3, 

116 p.

Leszcykowski, A.M., 1986, Mineral resources of the 

North Fork Owyhee River study area, Owyhee 

County, Idaho: U.S. Bureau of Mines Open-File 

Report MLA 10-86, 8 p.

Mabey, D.R., 1983, Geothermal resources of southern 

Idaho: U.S. Geological Survey Circular 866, 24 p.

MacDonald, Ray, and Bailey, B.C., 1973, Chapter N, 

Chemistry of igneous rocks, Part 1, The chemistry 

of the peralkaline oversaturated obsidians, in 

Fleischer, M., ed., Data of geochemistry, sixth 

ed.: U.S. Geological Survey Professional Paper 

440-N-l, 37 p.

Mathews, G.W., and Blackburn, W.H., 1982, Assessment of geology, energy, and mineral (GEM) 

resources, Pole Creek GRA resource area, (ID010-10), Owyhee County, Idaho: Prepared under 

U.S. Bureau of Land Management contract YA553-CT2-1042 by TERRADATA, Lakewood, Colo., 

37 p.

Minor, S.A., Sawatzky, Donnie, and Leszcykowski, 

A.M., 1986, Mineral resources of the North Fork 

Owyhee River Wilderness Study Area, Owyhee 

County, Idaho: U.S. Geological Survey Bulletin 

1719-A, 9 p.

Nerco, Inc., 1985, Securities and Exchange Commission 

Form 10-K, 26 p.

Oak Ridge Gaseous Diffusion Plant, 1982, Hydrogeochemical and stream sediment reconnaissance 

basic data for Jordan Valley quadrangle, Oregon

and Idaho: United States Department of Energy, 

Open-File Report GJBX-58(82), 97 p., 1 fiche.

Panze, A.J., Jr., 1975, Geology and ore-deposits of the 

Silver City-Delmar-Flint region, Owyhee County, 

Idaho: Idaho Bureau of Mines and Geology 

Pamphlet 161, 79 p.

Plouff, Donald, 1977, Preliminary documentation for a 

FORTRAN program to compute gravity terrain 

corrections based on topography digitized on a 

geographic grid: U.S. Geological Survey OpenFile Report 77-535.

Powers, H.A., 1947, Diatomite deposits of southwestern Idaho: Idaho Bureau of Mines and 

Geology Mineral Resources Report 4, 27 p.

Rogers, W.H., Moss, K.L., and Thomason, R.E., 1980, 

Delamar silver mine, Delamar, Idaho: Northwest 

Mining Association 86th Annual Convention, 8 p.

Rowan, L.C., and Purdy, T.L., 1984, Analysis of linear 

features in the Wallace, Idaho-Montana 1° x 2° 

quadrangle: U.S. Geological Survey Miscellaneous 

Field Studies Map MF-1354-H, 38 p.

Sandberg, C.A., 1983, Petroleum potential of wilderness lands in Idaho: U.S. Geological Survey 

Circular 902-F, 6 p.

Sawlan, M.G., King, H.D., Hoffman, J.D., Kulik, D.M., 

Gabby, P.N., Capstick, D.O., and Buehler, A.R., 

1987, Mineral resources of the Owyhee River 

Canyon and the Deep Creek-Owyhee River 

Wilderness Study Areas, Owyhee County, Idaho: 

U.S. Geological Survey Bulletin 1719-D, 12 p.

Staley, W.W., 1964, Diatomite, in Mineral and water 

resources of Idaho: Idaho Bureau of Mines and 

Geology Special Report 1, p. 74-79.

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, 1978, Aeromagnetic map of

Idaho: U.S. Geological Survey Geophysical

Investigations Map GP-919, scale 1:500,000, 1

sheet. 

Warner, M.M., 1980, S. Idaho, N. Nevada, southeastern

Oregon prime exploration target: Oil and Gas

Journal, v. 78, no. 18, p. 325-341.

G10
APPENDIXES
DEFINITION OF LEVELS OF MINERAL RESOURCE POTENTIAL 

AND CERTAINTY OF ASSESSMENT

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

o

Q. 

01

o 

cc

o 

o

(A

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.

40-42. 

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

Geological Survey Open-File Report 84-0787, p. 7, 8.

G12
RESOURCE/RESERVE CLASSIFICATION

IDENTIFIED RESOURCES

Demonstrated

Measured Indicated

Inferred

UNDISCOVERED RESOURCES

Probability Range

Hypothetical Speculative

ECONOMIC

SUBECONOMIC

Reserves Inferred 

Reserves

I

Marginal 

Reserves

I

Inferred 

Marginal 

Reserves

I

Demonstrated

Subeconomic

Resources

i

Inferred

Subeconomic

Resources

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.

G13
GEOLOGIC TIME CHART 

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

EON

Phanerozoic

Proterozoic

Archean

pre- Arc

ERA

Cenozoic

Mesozoic

Paleozoic

Late Proterozoic

Middle Proterozoic

Early Proterozoic

Late Archean

Middle Archean

Early Archean 

hean 2

PERIOD

Quaternary

Tertiary

Neogene 

Subperiod

Paleogene 

Subperiod

Cretaceous

Jurassic

Triassic

Permian

Carboniferous 

Periods

Pennsylvanian

Mississippian

Devonian

Silurian

Ordovician

Cambrian

 -(3800?)- -

EPOCH

Holocene

Pleistocene

Pliocene

Miocene

Oligocene

Eocene

Pateocene

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

u

- 24

oo

\j*j 

cc

- 96

100 

one

A.*tU

^\j\j 

_ f^'iin ""OOU

 tan

- 410

- 43R too

- 500

*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.

G14

GPO 585-045/77412
Minor and others MINI RAI Rl SOURCES, UPPER 1)1 IT CRI I K WIIDERNISS STUDY AREA. OVVYHt I COUNTY, IDAHO U.S. Geological Survey Bulletin 17 I 1