Mineral Resources of the

Hack Lake Wilderness Study Area,

Carfield County, Colorado

U.S. GEOLOGICAL SURVEY BULLETIN 1717-A

COLORADO

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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 unlikely. 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 intekpretations 

of data indicate a 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 occurrence, where interpretations of 

data indicate a high degree of likelihood for resource accumulation, where data support 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

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

o

Q_

U 

(T.

ID 

O 

C/D

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-^2. 

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.
Chapter A

MINERAL RESOURCES OF WILDERNESS STUDY AREAS 

NORTH-CENTRAL COLORADO

Mineral Resources of the

Hack Lake Wilderness Study Area,

Garfield County, Colorado

By Sandra J. Soulliere and Mark A. Arnold, 

U.S. Geological Survey, and

Steven E. Kluender, 

U.S. Bureau of Mines

U.S. GEOLOGICAL SURVEY BULLETIN 1717-A
DEPARTMENT OF THE INTERIOR 

DONALD PAUL MODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Library of Congress Catalog Number 85-600285

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1985

For sale by the Branch of Distribution 

U.S. Geological Survey 

604 South Pickett Street 

Alexandria, VA 22304
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 their 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 the Hack Lake (CO-070-425) Wilderness 

Study Area, Garfield County, Colorado.

CONTENTS

Summary 1 

Introduction 1

Investigations by the U.S. Bureau of Mines 1

Investigations by the U.S. Geological Survey 4 

Appraisal of identified resources 4

Mining and mineral-exploration activity 4 

Assessment of potential for undiscovered resources 4

Geology 4

Geochemistry 4

Mineral and energy resources 4 

References cited 5

FIGURES

1. Map of the Hack Lake Wilderness Study Area 2

2. Index map showing the location of the Hack Lake Wilderness Study Area

Contents

MINERAL RESOURCES OF WILDERNESS STUDY AREAS NORTH-CENTRAL COLORADO

Mineral Resources of the

Hack Lake Wilderness Study Area,

Garfield County, Colorado

By Sandra J. Soulliere and Mark A. Arnold 

U.S. Geological Survey and 

Steven E. Kluender 

U.S. Bureau of Mines

SUMMARY

The Hack Lake (CO-07(M25) Wilderness Study 

Area has no identified mineral resources, and low potential for undiscovered mineral resources including oil, 

gas, or coal. This conclusion is based on an earlier survey of the Flat Tops Wilderness (Mallory and others, 

1966) and on field investigations conducted in 1984.

The wilderness study area is about 20 mi northeast 

of Glenwood Springs, in Garfield County, Colo. It consists of two small plots of land that total about 10 acres 

adjoining the Flat Tops Wilderness in the White River 

National Forest. The wilderness study area consists of 

steep cliffs of basalt, 10,860 ft to 11,034 ft in altitude 

(fig. D.

An extensive geochemical sampling survey of the 

Flat Tops Wilderness included the Hack Lake Wilderness 

Study Area (Mallory and others, 1966). Analyses of 

stream-sediment samples, taken from streams which 

drain the Wilderness, revealed no anomalous concentrations of any elements. During the present field investigation, five representative rock samples were collected to 

evaluate the undiscovered mineral resource potential of 

the basalt which is the bedrock in the area. Geochemical 

analyses of the samples indicate that the basalt contains 

no anomalous concentrations of any elements indicative 

of mineralization.

No mines or prospects are in or adjacent to the 

wilderness study area. No mineralized areas were identified during field investigations. An examination of U.S. 

Bureau of Land Management and county records disclosed no patented or unpatented mining claims or mineral leases in or adjacent to the wilderness study area.

Based upon geochemical analyses, geological surveys, and the absence of mines, prospects, and 

mineralized areas, the wilderness study area is considered to have low mineral resource potential. Although 

gypsum and anhydrite may be present in the Middle and 

Upper Pennsylvanian Eagle Valley Evaporite, approximately 3,000 ft beneath the wilderness study area, the

potential for these resources is unknown. The Lower and 

Middle Pennsylvanian Belden Formation may contain 

beds of coaly shale approximately 4,000 ft beneath the 

wilderness study area, but the potential for coal resources is low. Thin coal beds in the Belden near the 

wilderness study area are discontinuous. Oil and gas potential is also considered low because the wilderness 

study area lacks favorable host rocks and structural traps 

for oil and gas. Host rocks favorable for the occurrence 

of uranium are not present.

INTRODUCTION

The Hack Lake (CO-070-425) Wilderness Study 

Area is about 20 mi northeast of Glenwood Springs, in 

Garfield County, Colo. (fig. 2). The area consists of two 

small plots of land of about 5 acres each adjoining the 

Flat Tops Wilderness in the White River National Forest. 

The area is accessible from White River National Forest 

trails on the northern and western boundaries and from 

the road along Sweetwater Creek to the south.

The wilderness study area is in the Colorado Plateau 

physiographic province at the southern edge of the Flat 

Tops Wilderness. The entire wilderness study area consists of steep basalt cliffs, 10,860 ft to 11,034 ft in altitude (fig. 1).

Investigations by the U.S. Bureau of Mines

In October 1983 the U.S. Bureau of Mines (USBM) 

conducted a mineral investigation to evaluate the identified mineral resources of the wilderness study area as 

part of a joint effort with the U.S. Geological Survey. 

U.S. Bureau of Land Management (BLM) and county records were examined for information regarding mining 

claims and leases in or adjacent to the wilderness study 

area. Published and unpublished information was reIntroduction
107°10' 107°07'30'

FLAT TOPS

WILDERNESS

QTb

APPROXIMATE BOUNDARIES

HACK LAKE WILDERNESS STUDY AREA

R 87 W

EXPLANATION

GLACIAL DEPOSITS _______ 

(QUATERNARY)

BASALT (QUATERNARY [_/ B 

AND TERTIARY)

BELDEN AND MOLAS FORMATIONS 

(PENNSYLVANIAN)

CONTACT

AREA OF LOW MINERAL

RESOURCE POTENTIAL-Data 

indicate geologic environment and 

suggest level of resource potential

Figure 1. Geologic and mineral resource potential map of the Hack Lake Wilderness Study Area (two locations), 

Garfield County, Colorado (geology modified from Bass and Northrop, 1963). Base from U.S. Geological Survey, 

Sweetwater Lake, Colo., 1977,1:24,000.

2 Mineral Resources of Wilderness Study Areas North-Central Colorado
107°30' 107°00'

39° 

45'

39' 

30'

APPROXIMATE BOUNDARY

OF THE FLAT TOPS

WILDERNESS

APPROXIMATE BOUNDARIES OF

THE HACK LAKE WILDERNESS

STUDY AREA

WHITE RIVER

NATIONAL FOREST

COLORADO

10MILES

Figure 2. Index map showing the location of the Hack Lake Wilderness Study Area, Garfield County, Colorado.

viewed; local residents and personnel from the USBM and search for any evidence of mines, prospects, or

the BLM were interviewed regarding minerals in the wil- mineralized areas in and within 0.5 mi of the wilderness

derness study area. A field investigation consisted of a study area.

Introduction 3
Investigations by the U.S. Geological Survey

In August 1984, the U.S. Geological Survey conducted an investigation to assess the potential for undiscovered mineral resources of the Hack Lake Wilderness 

Study Area. This assessment is based on published information on the Flat Tops Wilderness (Mallory and others, 

1966) and a field investigation of the wilderness study 

area. The study consisted of a review of published material; a field check of existing geologic mapping at a scale 

of 1:24,000; a search for mines, prospects, and 

mineralized areas; and rock sampling for geochemical 

analyses. Mineral resource potential was classified according to the system of Goudarzi (1984).

Acknowledgments. We thank the personnel of the 

U.S. Bureau of Land Management in Glenwood Springs 

for providing information on access to the wilderness 

study area and N. M. Conklin for analyses of the 

geochemical samples.

APPRAISAL OF IDENTIFIED RESOURCES 

By Steven E. Kluender, U.S. Bureau of Mines

Mining and Mineral-Exploration Activity

There are no mines or prospects in the wilderness 

study area, and no mining activity has occurred in or adjacent to it. Neither mineralized areas nor altered or stained 

areas indicative of mineralization were identified in or 

near the wilderness study area during the field investigation. An examination of BLM and county records disclosed no patented or unpatented mining claims or mineral 

leases in or adjacent to the wilderness study area at the 

time of the study. An oil-and-gas lease application has 

been filed in sec. 6, T. 3 S., R. 86 W., less than 2 

mi east of the wilderness study area (Kluender, 1984).

ASSESSMENT OF POTENTIAL FOR 

UNDISCOVERED RESOURCES 

By Sandra J. Soulliere and Mark A. Arnold, 

U.S. Geological Survey

Geology

The Hack Lake Wilderness Study Area is in the 

northeastern part of the White River Plateau, a broad 

northwest-trending dome of the Colorado Plateau physiographic province. The wilderness study area consists of 

steep cliffs of basalt, 10,860 ft to 11,034 ft in altitude.

Flat-lying Quaternary and Tertiary basalt lava flows 

(unit QTb, fig. 1) form the cliffs which make up the wilderness study area. The basalt consists of several separate 

flows, ranging from fine-grained andesitic basalt to vesicular basalt. Talus, composed of angular blocks of basalt,

covers the foot of the cliffs. Quaternary glacial moraine 

and outwash deposits (unit Qg) surround Hack Lake and 

are well below the study area (fig. 1).

Ordovician through Pennsylvanian sedimentary 

rocks exposed to the south may underlie the wilderness 

study area. Geologic formations which may be in the subsurface include the Pennsylvanian Belden and Molas Formations (unit Pbm, fig. 1) (base approximately 4,000 ft 

below the surface) and the Middle and Upper Pennsylvanian Eagle Valley Evaporite (base approximately 3,000 

ft below the surface). The depths to these formations were 

approximated using the published geologic map of the 

Glenwood Springs quadrangle by Bass and Northrop 

(1963).

Geochemistry

A geochemical survey to evaluate the mineral potential of the Flat Tops Wilderness included samples from 

streams which drain the Hack Lake Wilderness Study 

Area (Mallory and others, 1966). The analyses of these 

samples revealed no anomalous concentrations of any elements which might indicate outcropping mineralized 

rocks.

The present field investigation included the collection and analysis of five basalt samples representative of 

the bedrock of the area. These samples were pulverized 

to less than 100 mesh (0.0059 in.). The samples were 

then analyzed for 31 elements by the six-step, direct-current arc, optical-emission semiquantitative spectrographic 

method (Grimes and Marranzino, 1968). Geochemical 

analyses indicate that the basalt contains no anomalous 

concentrations of elements which might indicate mineralization.

Mineral and Energy Resources

No mineralized areas were identified in the wilderness study area; however, gypsum and anhydrite may be 

present in the Eagle Valley Evaporite. In the vicinity of 

Eagle, about 20 mi southeast of the study area, the Eagle 

Valley Evaporite is about 9,000 ft thick and contains isolated pods and lenses of gypsum and anhydrite (500- 

1,000 ft thick; Mallory, 1971). The Eagle Valley Evaporite thins northeast of Eagle and is not exposed in the 

study area. It may be present beneath a thick cover of 

basalt (base approximately 3,000 ft beneath the area). The 

resource potential for gypsum and anhydrite is unknown, 

because their extent beneath the wilderness study area is 

unknown.

The Belden Formation, approximately 4,000 ft beneath the wilderness study area, may contain beds of 

coaly shale. Bass and Northrop (1963) noted that coal 

in the Belden is discontinuous near the wilderness study

4 Mineral Resources of Wilderness Study Areas North-Central Colorado
area. They found a 9-in.-thick coal bed in an outcrop 

of the Belden near Sweetwater Creek about 3 mi south 

of the wilderness study area. The resource potential for 

coal is low because coal beds in the Belden are discontinuous. The wilderness study area lacks favorable host 

rocks and structural traps for oil and gas. The potential 

for uranium is low because the wilderness study area lacks 

host rocks favorable for uranium.

The low mineral resource potential in the wilderness 

study area is assigned a certainty level of B for all 

commodities because the distribution of occurrences 

in rocks beneath the area cannot be observed and has not 

been well defined near the wilderness study area.

REFERENCES CITED

Bass, N. W. and Northrop, S. A., 1963, Geology of the Glenwood Springs quadrangle and vicinity, northwestern Colorado: U.S. Geological Survey Bulletin 1142-J, 74 p.

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

Open-File Report 84-787, 42 p.

Grimes, D. L, and Marranzino, A. P., 1968, Direct-current arc 

and alternating-current spark emission spectrographic field 

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

Kluender, S. E., 1984, Mineral investigation of the Hack Lake 

Wilderness Study Area, Garfield County, Colorado: U.S. 

Bureau of Mines Open-File Report MLA 34-84, 7 p.

Mallory, W. W., 1971, The Eagle Valley Evaporite, northwest 

Colorado a regional synthesis: U.S. Geological Survey 

Bulletin 1311-E, 37 p., 3 pi.

Mallory, W. W., Post, E. V., Ruane, P. J., Lehmbeck, W. 

L., and Stotelmeyer, R. B., 1966, Mineral resources of the 

Rat Tops Primitive Area, Colorado: U.S. Geological Survey 

$ulletin 1230-C, 30 p., 2 pi.

References Cited

U. S. GOVERNMENT PRINTING OFFICE: 1985 676-047/26,005 REGION NO. 8