Mineral Resources of the

Cross Mountain Wilderness Study Area,

Moffat County, Colorado

U.S. GEOLOGICAL SURVEY BULLETIN 1759-A

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Chapter A

Mineral Resources of the

Cross Mountain Wilderness Study Area,

Moffat County, Colorado

By KARL V. EVANS, JAMES G. FRISKEN, and 

DOLORES M. KULIK 

U.S. Geological Survey

JOHN R.THOMPSON 

U.S. Bureau of Mines

U.S. GEOLOGICAL SURVEY BULLETIN 1759

MINERAL RESOURCES OF WILDERNESS STUDY AREASMISCELLANEOUS STATES
DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Any use of trade, product, or firm names in this publication is for descriptive 

purposes only and does not imply endorsement by the U.S. Government.

UNITED STATES GOVERNMENT PRINTING OFFICE: 1989

For sale by the

Books and Open-File Reports Section

U.S. Geological Survey

Federal Center

Box 25425

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Library of Congress Cataloging-in-Publication Data

Mineral resources of the Cross Mountain wilderness study area, Moffat County, 

Colorado / by Karl V. Evans ... [et al.].

p. cm. (Mineral resources of wilderness study areas miscellaneous states 

ch. A) (U.S. Geological Survey bulletin ; 1759A)

Bibliography: p.

Supt. of Docs, no.: I 19.3:1759-A

1. Mines and mineral resources Colorado Cross Mountain Wilderness. 

2. Cross Mountain Wilderness (Colo.) I. Evans, Karl V. II. Series. 

III. Series: U.S. Geological Survey bulletin ; 1759A. 

QE75.B9 no. 1759-A 

[TN24.C6] 

557.3 s dc20

[553'.09788'12] 89-600147

CIP
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 the Cross Mountain Wilderness Study 

Area (CO-010-230), Moffat County, Colorado.

CONTENTS

Abstract Al 

Summary Al

Character and setting Al 

Identified resources Al 

Mineral resource potential A2 

Introduction A3

Investigations by the U.S. Bureau of Mines A3 

Investigations by the U.S. Geological Survey A3 

Appraisal of identified resources A3 

Mining and leasing activity A3 

Mineral appraisal A4

Limestone and dolomite A4 

Iron oxide pigments A6 

Uranium A6 

Metals A6

Construction materials A6

Assessment of potential for undiscovered resources A6 

Geology A6 

Geochemistry All 

Geophysics All 

Mineral resource potential A13

Sediment-hosted copper A13 

Tabular uranium-vanadium A15 

Oil and gas A15

Coal and geothermal resources A15 

Other metals A16 

References cited A16 

Appendix A19

FIGURES

1. Index map showing the location of the Cross Mountain Wilderness Study 

Area A2

2. Summary map showing mineral resource potential of the Cross Mountain 

Wilderness Study Area A4

3. Map showing oil and gas leases and hematite prospects in and near the Cross 

Mountain Wilderness Study Area A7

4. Geologic map of the Cross Mountain Wilderness Study Area and 

vicinity A8

5. Complete Bouguer gravity and generalized structure map of the Cross 

Mountain Wilderness Study Area and vicinity A12

6. Residual-intensity aeromagnetic and generalized structure map of the Cross 

Mountain Wilderness Study Area and vicinity A14

Contents

MINERAL RESOURCES OF WILDERNESS STUDY AREAS-MISCELLANEOUS STATES

Mineral Resources of the

Cross Mountain Wilderness Study Area,

Moffat County, Colorado

By Karl V. Evans, James G. Frisken, and

Dolores M. Kulik

U.S. Geological Survey

John R. Thompson 

U.S. Bureau of Mines

ABSTRACT

The Cross Mountain Wilderness Study Area 

(CO-010-230) comprises about 14,081 acres in Moffat 

County, northwestern Colorado, between the town of Maybell and Dinosaur National Monument. The study area 

contains high-purity limestone of the Morgan Formation 

suitable for industrial and agricultural use; dolomitic limestone of the Madison Limestone suitable for agricultural use; 

and limestone, dolomite, sandstone, and sand and gravel 

suitable for use as construction materials. There has been no 

mining within the study area. The entire study area has low 

mineral resource potential for sediment-hosted copper in the 

Uinta Mountain Group, and parts of the study area have low 

resource potential for sandstone-type uranium-vanadium in 

sedimentary rocks of the Chinle Formation, Entrada and Glen 

Canyon Sandstones, Curtis Formation, Morrison Formation, 

and Browns Park Formation. The entire study area has low 

resource potential for all other metals and geothermal 

resources. It has high energy resource potential for oil and 

gas in the eastern part of the area and moderate potential 

elsewhere. The study area has no mineral resource potential 

for coal.

SUMMARY 

Character and Setting

The Cross Mountain Wilderness Study Area 

(CO-010-230), hereafter referred to as the "study area," 

comprises about 14,081 acres about 15 mi (miles) west of

Manuscript approved for publication March 10, 1989

Maybell, Moffat County, northwestern Colorado (fig. 1). As 

requested by the U.S. Bureau of Land Management, field 

work was conducted by the U.S. Geological Survey (USGS) 

and U.S. Bureau of Mines (USBM) to assess the mineral 

resource potential and appraise the identified mineral 

resources of the study area. Cross Mountain is on the 

southwestern edge of the Wyoming Basin physiographic 

province, a known producer of uranium, coal, and oil and 

gas. The Maybell uranium mining district is about 20 mi east 

of Cross Mountain, but the study area has no history of 

mining.

The Cross Mountain area is a fault-bounded, doubly 

plunging anticline cored by the Proterozoic Uinta Mountain 

Group (see geologic time chart in the Appendix of this 

report). Above the Uinta Mountain Group are several 

unconformity-bounded packages of Paleozoic and Mesozoic 

sedimentary rocks, which are in turn overlain by the Tertiary 

Bishop Conglomerate and Browns Park Formation. Faulting 

in the region probably occurred intermittently from the Middle 

Proterozoic to Tertiary time.

A geochemical study of stream sediments showed 

seven low-level anomalies, each of which was a singleelement anomaly representing a separate sample site. These 

are not considered indicative of mineral deposits.

Gravity and aeromagnetic results do correlate well with 

major regional structures identified by mapping at the 1° x 2° 

scale; however, they do not indicate the presence of any 

mineral resources in the study area.

Identified Resources

There are no identified resources in the study area, but 

dolomite and high-purity limestone are present. The Morgan

Cross Mountain Wilderness Study Area A1
40° 

40'

40° 

30'

40° 

20'

108° 30' 

I

108° 15' 

I

BOUNDARY OF 

MAYBELL MINING DISTRICT

APPROXIMATE BOUNDARY OF

THE CROSS MOUNTAIN

WILDERNESS STUDY AREA

(CO-010-230) A

CROSS 

MOUNTAIN

DINOSAUR

NATIONAL

MONUMENT

DANFORTH HILLS 

OILFIELD

ELK SPRINGS 

OILFIELD

TEMPLE CANYON 

OILFIELD

BOUNDARY OF 

MAYBELL MINING DISTRICT

5 MILES 

J

Figure 1 . Index map showing the location of the Cross Mountain Wilderness Study Area, Moffat County, Colo. Dashed lines 

are dirt roads.

Formation contains high-purity limestone, which could be 

used as a scrubber in local power plants, a purifier in the 

sugar beet industry, or as dusting in underground coal 

mines. The Madison Limestone could be used as agricultural 

dolomite, construction material, and aggregate.

Sandstone and sand and gravel are also present in the 

study area, but much larger and more accessible deposits 

are found in the lowlands outside the boundaries of the study 

area. Rocks were examined and sampled for evidence of 

metallic mineral deposition, but only low concentrations of 

metals were found. Hematite zones were examined for 

suitability for iron oxide pigments, but the concentrations of 

toxic and heavy metals are too high for commercial use.

Mineral Resource Potential

The entire Cross Mountain Wilderness Study Area is 

underlain by the Uinta Mountain Group, which has a low 

mineral resource potential, at certainty level C (fig. 2), for 

sediment-hosted copper. This conclusion is based on the 

lack of geochemical anomalies and only partial correlation 

with known mineral deposit models.

A low mineral resource potential, at certainty level C, for 

sandstone-type uranium-vanadium deposits is assigned to 

parts of the study area containing several stratigraphic units 

known to host such deposits in neighboring regions. This

A2 Mineral Resources of Wilderness Study Areas Miscellaneous States
evaluation is based on the lack of field and scintillometer 

evidence for uranium-vanadium deposition and on the 

presence of only one low-level vanadium anomaly.

The mineral resource potential for oil and gas is rated 

high in the eastern part of tne study area, at certainty level C, 

on the basis of geologic mapping, unpublished seismic data, 

and information from several wells drilled near the study area. 

The western part of the area is rated as having moderate 

energy resource potential because of the apparent lack of 

upturned units beneath the overhanging western margin of 

the Cross Mountain uplift. A certainty level of B is given 

because of the lack of direct drilling data.

No coal-bearing units are present within the study area; 

nor does available evidence suggest their presence at depth. 

Therefore the study area has no mineral resource potential 

for coal, at certainty level D. No thermal springs are present, 

and the area has low potential, at certainty level B, for 

geothermal resources. For all other metals, the geochemical 

data do not indicate significant single or multi-element 

anomalies and no appropriate deposit models fit the geologic setting. Therefore, the resource potential for all other 

metals is low, at certainty level B.

INTRODUCTION

The Cross Mountain Wilderness Study Area covers 

approximately 14,081 acres in Moffat County, northwestern Colorado (fig. 1). The study area is about 15 mi 

west of Maybell, Colo., and about 5 mi east of Dinosaur 

National Monument. U.S. Highway 40 and Colorado 

Highway 318 diverge near Maybell to pass south and 

north of Cross Mountain, respectively. Gravel roads 

nearly encircle Cross Mountain, providing ready access 

to the study area. The Little Snake River runs immediately west of the study area, and the Yampa River has 

carved Cross Mountain Canyon through the southern 

part of the area. Cross Mountain rises abruptly above the 

alluvial plain of the Little Snake River at about 5,650 ft 

(feet) to its highest point at 7,804 ft.

This report presents an evaluation of the mineral 

endowment (identified resources and mineral resource 

potential) of the study area and is the product of several 

separate studies by the U.S. Bureau of Mines and the 

U.S. Geological Survey. Identified resources are classified according to the system of the U.S. Bureau of Mines 

and U.S. Geological Survey (1980), which is shown in the 

Appendix of this report. Identified resources are studied 

by the USBM. Mineral resource potential is the likelihood of occurrence of undiscovered metals and nonmetals, industrial rocks and minerals, and of undiscovered energy resources (coal, oil, gas, oil shale, and 

geothermal sources). It is classified according to the 

system of Goudarzi (1984), which is shown in the 

Appendix of this report. The potential for undiscovered 

resources is determined by the USGS.

Investigations by the 

U.S. Bureau of Mines

The Cross Mountain Wilderness Study Area was 

examined by the USBM in 1987 (Thompson, 1988). Prior 

to the field investigation, a detailed literature search was 

made for pertinent geologic, mining, and land status 

information. U.S. Bureau of Land Management and 

county records were examined for locations of patented 

and unpatented mining claims and oil and gas leases in 

and near the study area. Ten employee-days were spent 

doing foot and vehicle reconnaissance including sampling 

of prospects and mineralized areas. Twenty-one rock 

samples and twenty-two stream-sediment samples of 

minus-80 mesh were collected for analysis.

All samples were analyzed for 27 elements and six 

limestone samples were subjected to whole-rock analysis 

by Chemex Labs, Inc., of Sparks, Nev., using inductively 

coupled plasma-atomic emission spectroscopy. Pertinent 

data are included in Thompson (1988), and detailed data 

may be obtained from the U.S. Bureau of Mines, 

Building 20, Denver Federal Center, Denver, CO 80225.

Investigations by the 

U.S. Geological Survey

The geology of the study area had been mapped 

previously by Dyni (1968) and McKay (1974) and was 

examined in reconnaissance in May 1987 for this study. A 

simplified geologic map of the study area is presented in 

this report; for more detailed information, consult the 

maps of Dyni (1968) and McKay (1974). Geochemical 

data were evaluated by J.G. Frisken and geophysical data 

were compiled by D.M. Kulik.

Acknowledgments. We would like to thank David 

Brady (BLM, Craig office) and Kermit Witherbee 

(BLM, Lakewood office) for providing information on 

the study area. Discussions with C.W. Spencer, P.R. 

Spencer, D.B. Seavey, D.S. Stone, J.J. Connor, CJ. 

Wandrey, T.J. Hainsworth, and A.R. Wallace are 

gratefully acknowledged.

APPRAISAL OF IDENTIFIED RESOURCES

By John R. Thompson 

U.S. Bureau of Mines

Mining and Leasing Activity

No mining has taken place and no mining claims 

are within the study area, although there are prospects 

and there has been mining nearby. The study area is near

Cross Mountain Wilderness Study Area A3
the Maybell mining district, where uranium has been 

mined in two areas. The major uranium-producing area 

is about 10 mi east of the study area and the smaller one 

is about 8 mi south of the study area (Collier and others, 

1978). The district has produced more than 1.6 million 

tons of ore from the Tertiary Browns Park Formation, 

which surrounds the study area. Although the Maybell 

mining district was inactive for many years, some of the 

old mines were reactivated in 1978 and about 200,000 

tons of ore were processed by heap-leaching (NelsonMoore and others, 1978, p. 253).

A few tons of limestone have been quarried for an 

undetermined use from the Pennsylvanian Morgan 

Formation about 1 mi south of the study area. This 

formation is highly fossiliferous and has been explored 

for marine invertebrate fossils. On the west boundary of 

the study area several iron oxide zones in limestone have 

been explored by bulldozing.

Drilling for hydrocarbons has been common in 

northwestern Colorado from the 1930's to the present. 

The Sand Wash basin to the north and the Piceance basin 

to the south both contain oil and gas fields that produce 

from formations of Pennsylvanian to Tertiary age (ScanIon, 1983). Within 22 mi of the study area, four fields in 

the Sand Wash basin have produced a combined total of 

more than 200 million MCF (thousand cubic feet) of gas 

and more than 5 million bbl (barrels) of oil. Within 18 mi 

of Cross Mountain, six fields in the Piceance basin have 

produced more than 14 million MCF of gas and more 

than 11 million bbl of oil (Scanlon, 1982, p. 26). Oil and 

gas leases covered almost the entire study area (fig. 3) as 

of May 1987 (Thompson, 1988).

Mineral Appraisal

outside the southern boundary of the wilderness study 

area, but the use of the quarried material is not known. 

Chemical analyses of three samples ranged from 87 to 97 

percent CaCO3 and from 0.8 to 7 percent MgCO3 . 

Combined CaCO3 and MgCO3 content ranged from 93 

to 98 percent. The Morgan Formation contains highpurity limestone suitable for a stack-gas scrubber in 

coal-fired power plants, mine dusting in coal mines, a 

purifier in sugar-beet refining, and agricultural 

limestone.

The Madison Limestone crops out in the northeastern and central parts of the study area. Three 

samples were collected and chemically analyzed. MgCO3 

content ranged from 24 to 39 percent and CaCO3 content 

ranged from 49 to 60 percent. Combined MgCO3 and 

CaCO3 content ranged from 84 to 92 percent. The 

Madison Limestone contains dolomitic limestone suitable for agricultural dolomite and aggregate.

Limestone samples were taken from outcrops, 

where weathering can affect the amount of calcium and 

other minerals present. An accurate assessment of the 

limestone can be ascertained only by excavating or core 

drilling into unweathered material. If subsurface 

sampling reveals higher calcium content, then both 

formations could be suitable for additional uses, such as 

cement.

Transportation is a significant factor in the cost of 

marketing limestone because it is a high-bulk, lowunit-value commodity. Trucking costs of high-purity limestone to coal-burning power plants at Craig (a distance of 

about 50 mi) would be about $6.00 per ton. The current 

price of limestone at the mine is about $35 per short ton; 

actual value and present mineability would depend on 

the saleability of the limestone based on local demand.

Limestone and Dolomite

Limestone is composed mostly of the mineral 

calcite (CaCO3 ), and dolomite is composed mostly of the 

mineral dolomite ((Ca,Mg)CO3 ). Ultrahigh-calcium 

limestone is more than 97 percent CaCO3 , high-calcium 

limestone is more than 95 percent CaCO3 , and highpurity dolomite is more than 95 percent (Ca,Mg)CO3 

and contains more than 47.5 percent magnesium 

carbonate. Dolomitic limestone containing 25-45 

percent magnesium carbonate is called "high magnesian," and that containing 5-25 percent magnesium 

carbonate is called "low magnesian" (Carr and Rooney, 

1983, p. 836).

In the study area, limestone occurs in the 

Pennsylvanian Morgan Formation and the Mississippian 

Madison Limestone. The Morgan Formation crops out 

in the northwestern and southern parts of the area. 

Limestone from this formation was quarried about 1 mi

EXPLANATION

[Entire study area has low mineral resource potential for sediment-hosted copper in the Uinta Mountain Group, at certainty level C; low mineral resource 

potential for all other metals not otherwise shown below, at certainty level B; 

low mineral resource potential for geothermal resources, at certainty level B; 

and no mineral resource potential for coal, at certainty level D]

H/C

M/B

L/C

B 

C

D

Geologic terrane having high mineral resource potential for 

oil and gas, at certainty level C

Geologic terrane having moderate mineral resource potential for oil and gas. at certainty level B

Geologic terrane having low mineral resource potential for 

sandstone-type uranium-vanadium deposits, at certainty level C

Levels of certainty 

Data indicate geologic environment and suggest level of

resource potential

Data indicate geologic environment and give good indication of level of resource potential, but do not establish 

activity of resource-forming processes 

Data clearly define geologic environment and level of 

resource potential and indicate activity of resourceforming processes in all or part of the area

A4 Mineral Resources of Wilderness Study Areas Miscellaneous States
108° 2 5'

40° 

30'

108° 20' 

I

APPROXIMATE BOUNDARY OF

THE CROSS MOUNTAIN

WILDERNESS STUDY AREA

(CO-010-230)

M/B 

L/C

2 MILES 

J

Figure 2 (above and facing page). Summary map showing mineral resource potential of the Cross 

Mountain Wilderness Study Area, Moffat County, Colo.

Cross Mountain Wilderness Study Area A5
Iron Oxide Pigments

Iron oxides are unique among mineral pigments 

because they are the only significant colored minerals 

found in a natural state and suitable for use as a pigment 

after being pulverized. Natural pigments are derived 

from iron oxide ore, are selected for their special physical 

and chemical properties, and can command a premium 

price. Color is the most important characteristic of a 

pigment. The chemical composition of the pigment is 

also important, as is the type and form of the minerals 

associated with it. For example, quartz would be undesirable because it would make grinding difficult, and 

calcination would be required to decompose organic 

matter (Hancock, 1983, p. 350).

Samples of two thin hematite zones were analyzed 

for their possible use as mineral pigments. In the 

northeast corner of the study area (fig. 3) a 1-ft-wide 

hematite zone in limestone has been exposed for about 

20 ft in a bulldozer cut. A sample from the zone 

contained 1.48 percent iron, 140 ppm (parts per million) 

arsenic, 42 ppm chromium, and 42 ppm molybdenum. 

On the western boundary of the study area, a 2-ft-wide 

hematite zone has also been exposed in a bulldozer cut 

(fig. 3). This zone contains some chert. A sample from 

the zone contains 0.97 percent iron and 252 ppm chromium (Thompson, 1988). These element concentrations 

are common in hematite zones and may not indicate any 

greater mineral concentration at depth.

Most pigmentary iron ore is chemically inert and 

contains only traces of heavy or toxic metals. Lead, 

antimony, arsenic, chromium, cadmium, mercury, and 

selenium should be at very low concentrations (Hancock, 

1983). Samples of the two hematite zones contained 

relatively high concentrations of some of these undesirable metals. Both hematite zones contain toxic metals 

and are too small and low in grade to be of use as mineral 

pigments.

Uranium

Uranium was produced near Maybell, about 10 mi 

east of the study area, where a crushing and sampling 

station operated until 1979 (Collier and others, 1978). 

Uranium was mined from the Tertiary Browns Park 

Formation, which is almost completely eroded from the 

study area. The Triassic Chinle Formation is the only unit 

in the area that is known to bear uranium elsewhere, and 

only a very thin zone crops out on the southwestern edge 

of the study area. The Chinle and other formations and 

structures in the study area were checked for radioactivity by a scintillometer, and samples were analyzed 

for uranium. The average background level for radiation 

in this area is 60 cps (counts per second); the highest 

scintillometer reading never exceeded 150 cps. All rock 

samples contained less than 10 ppm uranium. There are

no surface indications of uranium resources in the Chinle 

in the Cross Mountain study area.

Metals

Mineral deposits commonly occur along faults and 

altered zones. The northwest-trending faults and breccia 

zones in the western and northern parts of the study area 

were sampled for precious and base metals. Maximum 

concentrations of elements in the structures were 200 

ppm arsenic, 620 ppm barium, 280 ppm chromium, 13 

ppm copper, 42 ppm molybdenum, 4 ppm lead, 360 ppm 

vanadium, and 119 ppm zinc (Thompson, 1988). These 

concentrations are too low to be of economic interest.

Redbed sandstone elsewhere has been mined for 

copper and silver deposits, and five different redbed 

formations were sampled for these and other elements. 

Maximum concentrations of elements in the sandstone 

formations were 240 ppm barium, 238 ppm chromium, 2 

ppm copper, 4 ppm molybdenum, and 29 ppm zinc 

(Thompson, 1988). Analytical data for samples from the 

structures and the sandstone do not indicate any 

economic mineral concentrations.

Construction Materials

Limestone, dolomite, sandstone, and sand and 

gravel exist in the study area. The high-purity limestone 

in the Morgan Formation and dolomitic limestone in the 

Madison Limestone are suitable for construction 

aggregate and road metal. Sandstone beds in the Uinta 

Mountain Group and Lodore Formation, which have a 

wide range of textures, colors, and chemical and physical 

properties, are suitable for use as dimension or building 

stone. Small occurrences of sand and gravel are common 

on the east and west sides of Cross Mountain where 

alluvium and colluvium have washed down from higher 

elevations. The access to the sandstone near the core of 

the Cross Mountain anticline is difficult, and vast 

quantities of sand and gravel are available at the flood 

plain of the Yampa and Little Snake Rivers. The difficult 

access to the sandstone and small quantity of sand and 

gravel preclude any likely development.

ASSESSMENT OF POTENTIAL FOR 

UNDISCOVERED RESOURCES

By Karl V. Evans, James G. Frisken, and

Dolores M. Kulik

U.S. Geological Survey

Geology

The Cross Mountain Wilderness Study Area is on 

a north-northwest-trending, doubly plunging anticline 

that lies directly between the southeast-trending axis of

A6 Mineral Resources of Wilderness Study Areas Miscellaneous States
108°25'

EASTERN AMERICAN 

SNAKE RIVER NO.1 1-14

EASTERN AMERICAN 

SNAKE RIVERNQ12-14

108" 20'

__

V

APPROXIMATE BOUNDARY OF 

THE CROSS MOUNTAIN 

WILDERNESS STUDY AREA 

(CO-010-230}

EXPLANATION

Oil and gas lease

X Hematite prospect 

-<J>- Oil drill hole 

_________I_________

2 MILES 

J

Figure 3. Map showing oil and gas leases and hematite prospects in and near the Cross Mountain Wilderness 

Study Area, Moffat County, Colo.

Cross Mountain Wilderness Study Area A7
CORRELATION OF MAP UNITS

Qu

nconformi

Tbp

nconformi

Tb

nconformi

Km

Kd

nconformi

Jm

nconformi

Jc

nconformi

J-fceg

nconformi

~fcc

nconformi

"fcPmp

PPw

Pm

r Holocene

ty

} Miocene and 

Oligocene

ty

> Oligocene

ty

f Upper Cretaceous

I

r Lower Cretaceous

-/

ty

r Upper Jurassic

ty

> Middle Jurassic

ty

~) Middle and 

Lower Jurassic

ty

 Upper Triassic

ty

> Lower Triassic

1 Middle 

r Pennsylvanian

nconformity(?)

PMs

nconformi

Mm

nconformi

Cl

nconformi

Yu

} Lower Pennsylvanian and 

Upper Mississippian(?)

ty

> Lower Mississippian

ty

>- Upper Cambrian

ty

>- Middle Proterozoic

\- QUATERNARY 

 Tbp

Tb

Km 

- TERTIARY 

Kd

Jm

Jc

- CRETACEOUS J^eg 

Tic 

"fcPmp

PPw

- JURASSIC Pm

PMs

Mm 

Cl

Yu 

- TRIASSIC

^ PERMIAN A * 

- PENNSYLVANIAN

- MISSISSIPPIAN

 CAMBRIAN 

- PROTEROZOIC

LIST OF MAP UNITS

Alluvium, colluvium, landslide, and terrace debris (Holocene) 

Browns Park Formation (Miocene and Oligocene)

Bishop Conglomerate (Oligocene) 

Mancos Shale (Upper and Lower Cretaceous) 

Dakota Sandstone (Lower Cretaceous) 

Morrison Formation (Upper Jurassic) 

Curtis Formation (Middle Jurassic)

Entrada Sandstone (Middle Jurassic) and Glen Canyon

Sandstone (Lower Jurassic and Upper Triassic) 

Chinle Formation (Upper Triassic)

Moenkopi Formation (Lower Triassic) and Park City Formation (Permian) 

Weber Sandstone (Permian and Pennsylvanian)

Morgan Formation (Middle Pennsylvanian)

Shale, sandstone, limestone, and dolomite (Lower Pennsylvanian and Upper Mississippian(?)) 

Madison Limestone (Lower Mississippian)

Lodore Formation (Upper Cambrian)

Uinta Mountain Group (Middle Proterozoic) 

Contact

Fault Dotted where concealed; dashed where approximately located

Reverse fault Dotted where concealed; dashed where approximately located; sawteeth on upper plate

Figure 4 (above and facing page). Geologic map of the Cross Mountain Wilderness Study Area and vicinity, Moffat 

County, Colo. Geology simplified from Dyni (1968) and McKay (1974).

the eastern Uinta anticline (to the west) and the Axial 

Arch (to the east). The region is characterized by 

complex structures related to (1) formation of the Uinta 

Mountain aulacogen in the Proterozoic, (2) thrusting of 

both the northern and southern margins of the Uinta 

Mountains in the Mesozoic and Tertiary, and (3) subsequent normal faulting during the Tertiary (Gries, 

1983a; Hansen, 1986a,b; Stone, 1986). Cross Mountain is 

essentially a "pop-up" block bounded by reverse faults on 

its east and west sides (fig. 4), as indicated by unpublished seismic lines and several oil wells drilled adjacent 

to the study area.

An incomplete stratigraphic section of Proterozoic 

through Tertiary rocks is present in the study area. The 

Middle Proterozoic Uinta Mountain Group is exposed 

primarily in the northern part of the study area, as well as 

in Cross Mountain Canyon, where erosion by the Yampa 

River has breached the anticline. The strata are reddishbrown, fine- to coarse-grained (in places conglomeratic) 

sandstone and arkose with minor interbeds of red shale.

A8 Mineral Resources of Wilderness Study Areas Miscellaneous States
108° 2 5' 108°20'

EASTERN AMERICAN 

BOON E DRAW NO.

. EASTERN AMERICAN 

V" SNAKE RIVER NO. 1 1-14

EASTERN AMERICAN 

SNAKE RIVER N0.1 2 -14

APPROXIMATE BOUNDARY OF

THE CROSS MOUNTAIN

WILDERNESS STUDY AREA

(CO-010-230)

2 MILES 

J

Cross Mountain Wilderness Study Area A9
Bedding is generally thick and strongly cross stratified. 

Maximum thickness in the study area is about 1,200 ft 

(McKay, 1974).

The Cambrian Lodore Formation unconformably 

overlies the Uinta Mountain Group with an angular 

discordance of about 8° in the study area (Kanizay, 1956), 

and its exposure closely follows that of the underlying 

Proterozoic rocks. The Lodore is light-gray and palegreen, glauconitic, fine- to coarse-grained sandstone and 

conglomeratic sandstone containing a few beds of red 

and green siltstone. The sandstone is thin to thick bedded 

and cross stratified. The maximum thickness is about 

300 ft.

Mississippian Madison Limestone caps the crest of 

central Cross Mountain and is also exposed at the 

northwestern tip of the range. The formation is lightgray, partly brecciated, micro crystalline dolomitic limestone and dolomite that unconformably overlies the 

Lodore Formation. It generally is massive and forms 

thick cliffs and ledges. The maximum thickness is about 

430 ft.

Unconformably above the Madison are Mississippian and Pennsylvanian sandstone, shale, limestone, and 

dolomite. This assemblage of lithologies is also found in 

three formal units, the Humbug Formation, Doughnut 

Shale, and Round Valley Limestone, which are the most 

likely correlatives (neither Dyni (1968) nor McKay 

(1974) assigned a formal stratigraphic name). Because 

these three formal units are composed of mixed lithologies, further work would be needed to separate and map 

the units in the field. The strata consist of interbedded 

gray dolomite containing red nodular chert, red and 

green shale, and earthy siltstone. These strata are poorly 

exposed and their maximum thickness is estimated at 

about 150 ft.

The Pennsylvanian Morgan Formation unconformably^) overlies the shale and dolomite unit and is 

exposed at the northwestern and southern tips of the 

range. The Morgan is primarily a gray fossiliferous 

limestone containing abundant nodular red chert. Interbedded with the dominant lithology are yellowish-brown, 

crossbedded sandstone and lesser amounts of gray, red, 

and green shale. The maximum thickness is about 

1,000 ft.

In northwestern Colorado the Morgan Formation 

is usually overlain conformably by the Permian Park City 

Formation and Triassic Moenkopi Formation. However, 

within the study area these units have been removed by 

faulting and will not be described here.

The Triassic Chinle Formation, which normally 

overlies the Moenkopi Formation unconformably, is 

present in the study area in two small fault blocks on the 

southwest side of the range. The Chinle is reddish brown 

overall but includes gray, green, and yellow interbeds. 

Lithologies are interbedded claystone, siltstone, sandstone, and mudstone-pebble conglomerate. The thickness regionally is about 285 ft.

The Triassic and Jurassic Glen Canyon Sandstone, 

which unconformably overlies the Chinle, and the unconformably overlying Jurassic Entrada Sandstone were 

mapped as one unit and crop out in several locations 

along the western margin of Cross Mountain. The rocks 

are grayish-orange, fine-grained to very fine grained, 

festoon crossbedded sandstone. A chert-pebble zone a 

few inches thick probably marks the regionally extensive 

J-2 unconformity (Pipiringos and O'Sullivan, 1978). The 

combined total thickness is about 700 ft.

The Jurassic Curtis Formation unconformably 

overlies the Entrada Sandstone and is exposed in the low 

hills in the west-central part of the range. The formation 

consists of interbedded olive-gray and greenish-gray, 

glauconitic sandstone, shale, and oolitic limestone. The 

thickness is about 100 ft.

Unconformably above the Curtis is the Jurassic 

Morrison Formation, present in the west-central part of 

the study area. The basal Morrison consists of white, 

lenticular crossbedded, well-sorted, medium-grained 

sandstone ranging from 40 to 150 ft in thickness. Above 

this are variegated siltstone and claystone containing 

lenses of poorly sorted gray sandstone (locally containing 

chert pebbles) and thin beds of light-gray limestone. The 

total thickness is about 500 ft.

The Cretaceous Dakota Sandstone unconformably 

overlies the Morrison and is divisible into three parts. 

The lower and upper parts consist of yellowish-brown to 

light-gray, medium- to coarse-grained, carbonaceous, 

quartzitic sandstone containing dark chert pebbles. 

Between these subdivisions are dark-greenish-gray and 

variegated, fissile shale. The total thickness varies from 

70 to 150 ft.

Conformably above the Dakota is the Cretaceous 

Mancos Shale, which is subdivided into the Lower 

Cretaceous Mowry Shale Member, Upper Cretaceous 

Frontier Sandstone Member, and Upper Cretaceous 

"main body." All are exposed in the study area on the 

west side of the range, but the Mowry and Frontier 

Members are extremely restricted in extent. The Mowry 

is primarily a gray siliceous shale containing numerous 

thin interbeds of bentonite; the thickness is about 100 ft. 

The Frontier consists of a lower unit of brownish-gray 

shale containing thin interbeds of bentonite and an upper 

unit of interbedded gray, fossiliferous, calcareous sandstone and gray shale. The thickness of the Frontier is 

about 200 ft. The main body of the Mancos Shale consists 

of dark-gray marine shale beds and thick sandstone beds 

near the top and bottom. The total thickness is about 

5,500 ft, but only the lower part is present in the study 

area.

Unconformably overlying older units is the Oligocene Bishop Conglomerate. Within and adjacent to the

A10 Mineral Resources of Wilderness Study Areas Miscellaneous States
study area this unit was mapped as part of the Browns 

Park Formation, but we follow Hansen (1986a) and 

Rowley and others (1985), who reinterpreted the earlier 

work of Dyni (1968) and McKay (1974). The Bishop is 

exposed on a high bench overlooking the Little Snake 

River along the western margin of Cross Mountain. It 

consists primarily of light-gray and pink, poorly to 

moderately consolidated, fluvial, partly tuffaceous conglomerate and sandstone. The thickness is variable but 

reaches a maximum of about 135 ft in the study area.

Cross Mountain is virtually encircled by strata of 

the Oligocene and Miocene Browns Park Formation, 

which unconformably overlie the Mancos Shale, as well 

as most of the other stratigraphic units mentioned previously. Within the study area, exposure of the Browns 

Park Formation is sparse but widespread. The Browns 

Park is white, light-gray, and tan, poorly to moderately 

consolidated, crossbedded, tuffaceous sandstone and 

conglomerate. Regionally, the thickness varies from 0 to 

1,600 ft.

Quaternary units are present as terrace deposits of 

sand and gravel capping pediment surfaces, landslide 

debris in Cross Mountain Canyon, colluvium developed 

on the steep flanks of the range, and alluvium along the 

Little Snake River.

Geochemistry

A reconnaissance geochemical survey of the study 

area was conducted by the U.S. Bureau of Land 

Management (BLM) between July and September of 

1983 (Witherbee, 1983). Twenty sediment samples of 

active alluvium were collected from first- and secondorder streams draining Cross Mountain. The samples 

were sieved to minus-80 mesh and were analyzed by 

Barringer Resources for 24 elements (Ag, As, Au, B, Ba, 

Be, Ca, Cu, Fe, F, Hg, Li, Mg, Mn, Mo, Pb, Sb, Sr, Th, Ti, 

U, V, W, and Zn) by atomic absorption, colorimetric, 

induction-coupled plasma emission spectrographic, neutron activation, or fluorometric methods having low 

detection limits. The sampling density and analytical 

methods employed by the BLM and Barringer Resources 

are comparable to those used by the USGS. Because of 

the lack of significant anomalies in the BLM studies and 

the additional surface sampling by the USBM, a decision 

was made by the USGS not to sample the study area 

further.

As part of the BLM study, frequency distribution 

histograms and log probability plots of cumulative 

frequency distribution were prepared for each element 

for 100 samples collected in the Cross Mountain and 

other wilderness study areas of this region. Threshold 

values were defined by inflection points on the plots.

Elements not present at concentrations above their 

detection limits (given in parentheses) are silver (0.1

ppm), gold (0.02 ppm), tungsten (4 ppm), antimony 

(1 ppm), and mercury (4 parts per billion)). Anomalous 

concentrations were found for molybdenum (one sample, 4 ppm), lead (one sample, 34 ppm), vanadium (one 

sample, 132 ppm), zinc (three samples, 64-92 ppm), and 

arsenic (one sample, 20 ppm). These concentrations are 

all low-level anomalies for the region and each is a 

single-element high representing a separate sample site. 

Witherbee (1983) did not give a threshold value for 

uranium, but most samples were below the detection 

limit of 0.2 ppm and the high value of 0.4 ppm is well 

below the average uranium concentration in sedimentary 

rocks (2 ppm).

Geophysics

Geophysical data provide information on the 

subsurface distribution of rock masses and the structural 

framework. Gravity and magnetic studies were undertaken as part of the mineral resource assessment of the 

Cross Mountain Wilderness Study Area. The geophysical 

data available for this study are generally sufficient only 

to identify regional features.

The gravity data were obtained in and adjacent to 

the study area in 1987 and were supplemented by data 

maintained in the files of the Defense Mapping Agency 

of the U.S. Department of Defense and by unpublished 

data obtained by D.M. Kulik during previous work in 

1986-87. Stations measured for this study were established by means of a Worden W-177 gravimeter. The 

data were tied to the International Gravity Standardization Net 1971 (U.S. Defense Mapping Agency Aerospace Center, 1974) at base station ACIC 1751-2 at 

Craig, Colo. Station elevations were obtained from benchmarks, spot elevations, and estimations from topographic 

maps at 1:24,000 scale and are accurate to ±20 ft. The 

error in the Bouguer gravity value is less than 1.2 mGal 

(milligals) for errors in elevation control. Bouguer 

anomaly values were computed by means of the 1967 

gravity formula (International Association of Geodesy, 

1967) and a reduction density of 2.67 g/cm3 (grams per 

cubic centimeter). Mathematical formulas are given in 

Cordell and others (1982). Terrain corrections were 

made by computer for a distance of 100 mi from the 

station using the method of Plouff (1977). The data are 

shown as a complete Bouguer gravity anomaly map in 

figure 5.

The aeromagnetic data are shown as a residualintensity magnetic anomaly map in figure 6 and are from 

the U.S. Department of Energy (Bendix Field Engineering Corporation, 1982). The survey was flown eastwest at an approximately 3-mi flight-line spacing and 

400 ft above the ground surface.

The study area lies on the gravity gradient between 

a major gravity low (A, fig. 5) associated with low-density

Cross Mountain Wilderness Study Area A11
108°

APPROXIMATE BOUNDARY OF

THE CROSS MOUNTAIN

WILDERNESS STUDY AREA

(CO-010-230)

10 MILES

Figure 5 (above and facing page). Complete Bouguer gravity and generalized structure map of the Cross Mountain 

Wilderness Study Area and vicinity. Structure from Rowley and others (1985).

A12 Mineral Resources of Wilderness Study Areas Miscellaneous States
EXPLANATION

 250 Gravity contours Contour interval 5 milligals; hachure!. indicate closed gravity low 

A Anomaly discussed in text

 G " Basin axis inferred from gravity data 

Gravity station

Measured for this study

From USGS published data

From U.S. Department of Defense 

> Anticline Arrow shows direction of plunge 

> Syncline Arrow shows direction of plunge

Thrust or reverse fault Dashed where covered or inf8rred;

sawteeth on upper plate

Normal fault Dashed where covered or inferred; bar ard ball 

on downthrown block

Tertiary rocks and higher values to the west where higher 

density Mesozoic, Paleozoic, and Precambrian rocks are 

exposed. The configuration of the gravity low suggests 

that the structural axis of the mapped syncline in the 

southeast corner of the map area (fig. 5) continues 

northward where indicated by the dashed line identified 

by the symbol "G." The gravity high in the southeast 

corner is associated with a mapped anticline and Paleozoic rocks of relatively high density that crop out at 

Juniper Mountain.

The study area lies on a north-trending gravity 

gradient that increases to the west and is associated with 

the eastern flank of the Douglas Creek arch, identified 

south of the study area (see Gries, 1983b, and Stone, 

1986, for location). The arch is interpreted from the 

gravity data to continue in the subsurface just west of the 

map area. The -240-mGal contour is deflected around 

the south end of the study area and an elongate enclosed 

gravity low borders the west side of the study area. This 

pattern results from uplift of high-density Paleozoic and 

Precambrian rocks along reverse faults having opposing 

dip, forming a minor "pop-up" structure. This structure 

may be on the leading edge of the fault system that 

bounds the Douglas Creek arch, but apparently is 

separated from that system by another north-trending 

fault. The gravity low along the southwestern part of the 

study area is caused by sedimentary rocks of relatively 

low density that thicken in a graben or faulted syncline 

between the study area and the main part of the Douglas 

Creek arch.

Magnetic data usually reflect differences in basement lithology or differences in depth to basement rocks. 

Two saddles in the magnetic data (A and B, fig. 6) al the 

extreme western edge of the map area mark the location 

of the north-trending fault that separates the main 

part of the Douglas Creek arch from Cross Mountain.

The study area lies on an east-west-trending magnetic 

gradient. The magnetic high (C) north of the study area 

extends westward over the core of the Uinta Mountains, 

where Precambrian rocks are exposed. The magnetic low 

(D) to the south is south of an east-northeast-trending 

fault system that passes south of the study area where 

only Mesozoic and Paleozoic rocks crop out. The 

gradient may mark the location of one of the bounding 

faults of the Proterozoic Uinta basin where there is a 

change in depth to basement rocks and possibly a change 

in lithology as well.

The magnetic high (E) in the southeast corner of 

the map area probably is caused by Precambrian 

crystalline rocks in the core of the anticline southwest of 

the Axial Basin fault system, where no Uinta Mountain 

Group rocks are preserved (Stone, 1986). The gap in 

subsurface Uinta Mountain Group rocks continues into 

the area of the relatively high magnetic arch (F). A 

relatively low anomaly (G) occurs northeast of the Axial 

Basin fault system, where as much as 10,000 ft of Uinta 

Mountain Group rocks are preserved and the depth to 

crystalline rocks is correspondingly greater and where 

nonmagnetic Paleozoic rocks are exposed at the surface.

Mineral Resource Potential

The geology of the study area permits the 

occurrence of several types of mineral and energy 

deposits, including stratiform copper in the Uinta 

Mountain Group and sandstone-type uranium-vanadium 

in several Mesozoic sandstone units and the Browns Park 

Formation.

Sediment-Hosted Copper

Sediment-hosted ("redbed"-type) copper deposits 

commonly occur in thick, red, sandy units throughout the 

world. Typically, these deposits form in association with 

underlying, or minor interbedded, mafic volcanic rocks; 

are associated with evidence of an arid depositional 

environment, such as salt casts or evaporitic rocks 

(gypsum, for example); and occur at or near a chemically 

reduced (generally organic rich) unit interbedded with 

the dominant redbeds (Gustafson and Williams, 1981). 

Although the Uinta Mountain Group is a thick redbed 

sequence that underlies the entire study area, it lacks 

most of the other characteristics for such sedimenthosted deposits. This information, combined with the 

geochemical data, indicates that the Uinta Mountain 

Group in the study area has a low mineral resource 

potential at certainty level C for sediment-hosted copper 

deposits (fig. 2).

Cross Mountain Wilderness Study Area A13
108°

APPROXIMATE BOUNDARY OF

THE CROSS MOUNTAIN

WILDERNESS STUDY AREA

(CO-010-230)

10 MILES

Figure 6 (above and facing page). Residual-intensity aeromagnetic and generalized structure map of the Cross 

Mountain Wilderness Study Area and vicinity. Structure from Rowley and others (1985).

A14 Mineral Resources of Wilderness Study Areas Miscellaneous States
 400

EXPLANATION

Magnetic contours Contour interval 20 nanoteslas; hachures

indicate area of closed magnetic low 

A Anomaly discussed in text

Anticline Arrow shows direction of plunge 

Syncline Arrow shows direction of plunge

Thrust or reverse fault Dashed where covered or inferred;

sawteeth on upper plate 

Normal fault Dashed where covered or inferred; bar and ball

on downthrown block

Tabular Uranium-Vanadium

Sandstone-type uranium-vanadium deposits are 

classically displayed on the Colorado Plateau south of 

Cross Mountain (Fisher, 1955; Nash and others, 1981) 

and to the east near Maybell (Chenoweth, 1987). The 

general model for deposition of these deposits requires 

leaching of uranium-vanadium, possibly from intercalated tuff beds in the sedimentary sequence, and deposition as primary ore minerals in a chemically reducing 

environment (Nash and others, 1981; Brownfield and 

others, 1986). In the study area possible host units for 

such deposits include the Chinle Formation, Entrada and 

Glen Canyon Sandstones, Curtis Formation, Morrison 

Formation, and Browns Park Formation. However, rock 

sample data and scintillometer surveys give no indication 

of uranium-vanadium mineralization at the surface and 

only one sample yielded a low-level vanadium anomaly. 

Therefore, the Chinle Formation, Entrada and Glen 

Canyon Sandstones, and Curtis, Morrison, and Browns 

Park Formations are rated as having a low mineral 

resource potential at certainty level C for sandstone-type 

uranium-vanadium deposits (fig. 2).

Oil and Gas

The oil and gas potential of the study area was 

rated as "zero" by Spencer (1983a,b), apparently because 

the Proterozoic Uinta Mountain Group is exposed in the 

core of the range. Based on data from recent wells drilled 

near the area and unpublished industry seismic studies, 

our evaluation differs from that of Spencer. We emphasize, however, that unlike Spencer's terminology, the 

ratings used in this report (see Appendix) evaluate only 

the energy resource potential for undiscovered oil and 

gas and carry no connotation as to the amount of any oil 

or gas that may be present.

Spencer (1983a) listed four critical factors required 

for hydrocarbon accumulations: (1) reservoir (poious) 

rocks, (2) hydrocarbon (organic-rich) source beds, (3) a 

relatively impermeable seal or barrier to prevent upward 

and lateral migration of hydrocarbons, and (4) favorable

thermal history. All of these factors are met within or 

immediately adjacent to the eastern part of the study 

area.

Within the wilderness study area the typical 

reservoir and source rocks of the region (the 

Pennsylvanian strata) are exposed, which generally would 

negate any oil potential. However, drilling adjacent to the 

eastern margin of the study area indicates the presence of 

both reservoir and source beds beneath the Browns Park 

Formation.

Seismic and well data indicate that Cross Mountain 

is bounded on both sides by inward-dipping reverse 

faults, thereby forming a "pop-up" structure. Both faults 

probably dip in excess of 50°, but the easternmost fault is 

thought to dip less steeply than the westernmost fault. 

The Eastern American Snake River No. 12-14 well, 

located about 0.5 mi east of the northern tip of the study 

area (fig. 4), penetrated the Browns Park Formation and 

Uinta Mountain Group, went through a complex fault 

zone into steeply dipping, overturned Morgan, Weber, 

Moenkopi, and Morrison rocks, and finally encountered 

upright Morrison and older units, bottoming at 10,261 ft 

in the Weber Sandstone. Oil stains were common in both 

the overturned and upright sections. Similar results, as 

well as a good oil show in the Morrison(?) Formation and 

Dakota Sandstone (D.B. Seavey, Braxton and Associates, 

oral commun., 1988), were found in the nearby Eastern 

American Snake River No. 11-14 well. It is evident from 

the oil show and the numerous oil stains in the cored 

holes that appropriate thermal conditions for the generation of oil existed in the area.

Current work by the petroleum industry, essentially all unpublished, seems to indicate that a sandstone 

reservoir body forms a stratigraphic trap immediately 

east of the study area. In addition, part of this stratigraphic trap may lie beneath the structural overhang 

penetrated by the Eastern American Snake River wells. 

These data suggest that the mineral resource potential 

for oil and gas is high, at certainty level C, in the eastern 

part of the study area. The remainder of the area is given 

a moderate potential, at certainty level B, because seismic results do not appear to show an upturn of units 

beneath the overhang at the west side of Cross Mountain 

(fig- 2).

Coal and Geothermal Resources

No coal-bearing units are present within the study 

area and available information does not suggest their 

presence at depth. The study area thus has no mineral 

resource potential for coal, at certainty level D. No 

thermal springs are present, and the area has low 

potential, at certainty level B, for geothermal resources 

(fig- 2).

Cross Mountain Wilderness Study Area A15
Other Metals

For all metals other than those mentioned previously, the geochemical data do not indicate significant 

single or multi-element anomalies, no appropriate 

mineral deposit models fit the geologic setting, and there 

is no past production. Therefore, for these metals the 

area has a low mineral resource potential at certainty 

level B (fig. 2).

REFERENCES CITED

Bendix Field Engineering Corporation, 1982, Vernal quadrangle, residual-intensity magnetic anomaly contour map, 

pi. 4 of Magnetic maps of Vernal, Utah/Colorado: U.S. 

Department of Energy Open-File Report GJM-289, 4 

sheets, scale 1:250,000; available from U.S. Geological 

Survey, Open-File Services Section, P.O. Box 25425, 

Denver, CO 80225.

Brownfield, M.E., Brownfield, I.K., and Foord, E.E., 1986, 

Geology and mineralogy of uranium-vanadium deposits 

in the Skull Creek area, Colorado, in Stone, D.S., ed., 

New interpretations of northwest Colorado geology: 

Denver, Colo., Rocky Mountain Association of Geologists, p. 293-295.

Carr, D.D., and Rooney, L.F., 1983, Limestone and dolomite, 

in Lefond, S.J., ed., Industrial minerals and rocks, 5th ed., 

vol. 2: New York, Society of Mining Engineers of the 

American Institute of Mining, Metallurgical, and 

Petroleum Engineers, Inc., p. 833-880.

Chenoweth, W.L., 1986, Geology and production history of the 

uranium deposits in the Maybell, Colorado, area, in 

Stone, D.S., ed., New interpretations of northwest Colorado geology: Denver, Colo., Rocky Mountain Association of Geologists, p. 289-292.

Collier, J.D., Hornbaker, A.L., and Chenoweth, W.L., 1978, 

Directory of Colorado uranium and vanadium mining 

and milling activities: Colorado Geological Survey Map 

Series 11, scale 1:500,000.

Cordell, L., Keller, G.R., and Hildenbrand, T.G., 1982, 

Bouguer gravity map of the Rio Grande Rift, Colorado, 

New Mexico, and Texas: U.S. Geological Survey Geophysical Investigations Series Map GP-949, scale 

1:1,000,000.

Dyni, J.R., 1968, Geologic map of the Elk Springs quadrangle, 

Moffat County, Colorado: U.S. Geological Survey 

Geologic Quadrangle Map GQ-702, scale 1:62,500.

Fisher, R.P., 1955, Uranium-vanadium-copper deposits of the 

Colorado Plateau, in Page, L.R., Stocking, H.E., and 

Smith, H.B., ed., Contributions to the geology of uranium 

and thorium by the United States Geological Survey and 

Atomic Energy Commission for the United Nations 

International Conference on Peaceful Uses of Atomic 

Energy, Geneva, Switzerland, 1955: U.S. Geological 

Survey Professional Paper 300, p. 143-154.

Goudarzi, G.H., compiler, 1984, Guide to the preparation of 

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

Survey Open-File Report 84-787, 42 p.

Gries, R., 1983a, Oil and gas prospecting beneath Precambrian 

of foreland thrust plates in Rocky Mountains: American 

Association of Petroleum Geologists Bulletin, v. 67, 

p. 1-28.

____ 1983b, North-south compression of Rocky Mountain 

foreland structures, in Lowell, J.D., and Gries, R., eds., 

Rocky Mountain foreland basins and uplifts: Denver, 

Colo., Rocky Mountain Association of Geologists, 

p. 9-32.

Gustafson, L.B., and Williams, N., 1981, Sediment-hosted 

stratiform deposits of copper, lead, and zinc: Economic 

Geology, Seventy-fifth Anniversary Volume, p. 139-178.

Hancock, K.R., 1983, Mineral pigments, in Lefond, S.J., ed., 

Industrial minerals and rocks, 5th ed., vol. 1: New York, 

Society of Mining Engineers of the American Institute of 

Mining, Metallurgical, and Petroleum Engineers, Inc., 

p. 349-372.

Hansen, W.R., 1986a, Neogene tectonics and geomorphology 

of the eastern Uinta Mountains in Utah, Colorado, and 

Wyoming: U.S. Geological Survey Professional Paper 

1356, 78 p.

____ 1986b, History of faulting in the eastern Uinta 

Mountains, Colorado and Utah, in Stone, D.S., ed., New 

interpretations of northwest Colorado geology: Denver, 

Colo., Rocky Mountain Association of Geologists, 

p. 5-17.

International Association of Geodesy, 1967, Geodetic reference system, 1967: International Association of Geodesy 

Special Publication No. 3, 116 p.

Kanizay, S.P., 1956, Geology of Cross Mountain, Moffat 

County, Colorado: Golden, Colorado School of Mines, 

Ph.D. thesis, 129 p.

McKay, E.J., 1974, Geologic map of the Lone Mountain 

quadrangle, Moffat County, Colorado: U.S. Geological 

Survey Geologic Quadrangle Map GQ-1144, scale 

1:62,500.

Nash, J.T., Granger, H.C., and Adams, S.S., 1981, Geology and 

concepts of genesis of important types of uranium 

deposits: Economic Geology, Seventy-fifth Anniversary 

Volume, p. 63-116.

Nelson-Moore, J.L., Collins, D.B., and Hornbaker, A.L., 1978, 

Radioactive mineral occurrences of Colorado and 

bibliography: Colorado Geological Survey Bulletin 40, 

1054 p.

Pipiringos, G.N., and O'Sullivan, R.B., 1978, Principal unconformities in Triassic and Jurassic rocks, western interior 

United States A preliminary survey: U.S. Geological 

Survey Professional Paper 1035-A, 29 p.

Plouff, D., 1977, Preliminary documentation for a FORTRAN 

program to compute gravity terrain corrections based on 

topography digitized on a geographic grid: U.S. 

Geological Survey Open-File Report 77-535.

Rowley, P.D., Hansen, W.R., Tweto, O., and Carrara, P.E., 

1985, Geologic map of the Vernal I°x2° quadrangle, 

Colorado, Utah, and Wyoming: U.S. Geological Survey 

Miscellaneous Investigations Series Map 1-1526, scale 

1:250,000.

Scanlon, A.H., 1982, Oil and gas fields of Colorado, statistical 

data through 1981: Colorado Geological Survey Information Series 18, 71 p.

A16 Mineral Resources of Wilderness Study Areas Miscellaneous States
____ 1983, Oil and gas fields map of Colorado: Colorado 

Geological Survey Map Series 22, scale 1:500,000.

Spencer, C.W., 1983a, Petroleum potential of wilderness lands 

in Colorado: U.S. Geological Survey Circular 902-E, 8 p.

____ 19835, Petroleum potential of wilderness lands, Colorado: U.S. Geological Survey Miscellaneous Investigations Series Map 1-1539, scale 1:1,000,000.

Stone, D.S., 1986, Seismic and borehole evidence for important 

pre-Laramide faulting along the Axial Arch in northwest 

Colorado, in Stone, D.S., ed., New interpretations of 

northwest Colorado geology: Denver, Colo., E.ocky 

Mountain Association of Geologists, p. 19-36.

Thompson, J.R., 1988, Mineral resources of the Cross 

Mountain Wilderness Study Area (CO-010-230), Moffat County, Colorado: U.S. Bureau of Mines Oper, File 

Report MLA 19-88, 25 p.

U.S. Bureau of Mines, 1987, Bureau of Mines cost estimating 

system handbook [in two parts] Part 1, Surface and 

underground mining: U.S. Bureau of Mines Information 

Circular IC-9142, p. 224-225.

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. Defense Mapping Agency, Aerospace Center, 1974, 

World relative gravity reference network, North America, Part 2: Defense Mapping Agency Aerozpace Center 

Reference Publication 25, with supplement updating 

Gravity Standardization Net, 1971, 1635 p.

Witherbee, K.G., 1983, Geology and mineral resource potential 

of the Cross Mountain Wilderness Study Area, Moffat 

County, Colorado (GEM, Phase 1 and 2): U.S. Bureau of 

Land Management unpublished report, 25 p.

Cross Mountain Wilderness Study Area A17

APPENDIX
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 interpretations 

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.

LLJ 

O

cc 

O

CO 

LU 

QC

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 84-4)787, p. 7, 8.
RESOURCE/RESERVE CLASSIFICATION

ECONOMIC

MARGINALLY 

ECONOMIC

SUBECONOMIC

IDENTIFIED RESOURCES

Demonstrated

Measured Indicated

Reserves

- 1 

Marginal Reserves

Demonstrated 

Subeconomic Resources

Inferred

Inferred Reserves

Inferred 

Marginal Reserves

Inferred 

Subeconomic 

Resources

UNDISCOVERED RESOURCES

Probability Range

 (or) 

Hypothetical i Speculative

I

1

1 

1

Major elements of mineral resource classification, excluding reserve base and inferred reserve base. Modified from McKelvey,1972, Mineral 

resource estimates and public policy: American Scientist, v.60, p.32-40, and 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.
GEOLOGIC TIME CHART 

Terms and boundary ages used 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 j

PERIOD

Quaternary

Neogene 

Subperiod

Tertiary 

Paleogene 

Subperiod

Cretaceous

Jurassic

Triassic

Permian

Pennsylvanian 

Carboniferous

Periods 

Mississippian

Devonian

Silurian

Ordovician

Cambrian

__ __ 3S00?_ -

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

_ _

BOUNDARY AGE 

IN 

MILLION YEARS

-0.010

- 1.7

- 5

- 24

- 55

cc

- 96

I *5o

-/v 240

- 290

«* . *5*5rt

- 410

- 500 

- ~ 570'

- 900

- 1600

- 2500

-3000 

- 3400

1 Rocks older than 570m.y. also called Precambrian, a time term without specific rank.

2 Informal time term without specific rank.

*U.SOPO:1989 673-047/86,101
SELECTED SERIES OF U.S. GEOLOGICAL SURVEY PUBLICATIONS

Periodicals

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Professional Papers are mainly comprehensive scientific reports of 

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collections of related papers addressing different aspects of a single scientific topic.

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geographic coverage than Professional Papers. They include the results 

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in relation to specific mining or mineral-deposit problems; post-1971 

maps are primarily black-and-white maps on various subjects such as 

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Hydrologic Investigations Atlases are multicolored or black-andwhite maps on topographic or planimetric bases presenting a wide range 

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is 1:24,000 and regional studies are at 1:250,000 scale or smaller.

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