Petroleum Potential of 

Wilderness Lands in 

Colorado 

By Charles W. Spencer 

PETROLEUM POTENTIAL OF WILDERNESS LANDS IN THE 

WESTERN UNITED STATES 

GEOLOGICAL SURVEY CIRCULAR 902-E 

This chapter on the petroleum 

geology and resource potential of 

Wilderness Lands in Colorado is 

also provided as an accompanying 

pamphlet for Miscellaneous Investigations Series Map 1-1539 

CONTENTS 

Page 

Abstract---------------------------------------------------------------------- E1 

Introduction------------------------------------------------------------------- 1 

Acknowledgments-------------------------------------------------------------- 2 

~ethodsofevaluation----------------------------------------------------------- 2 

Petroleum province potentials --------------------------------------------------- 4 

Raton Basin-Sierra Grande Uplift province-------------------------------------- 4 

Albuquerque-Santa Fe-San Luis Rift Basins province ----------------------------- 5 

San Juan Basin province ----------------------------------------------------- 5 

Paradox Basin province ------------------------------------------------------ 5 

Uinta-Piceance-Eagle Basins province ------------------------------------------ 6 Park Basins province _____ ..:___________________________________________________ 7 

Southwestern Wyoming Basins province----------------------------------------- 7 

Summary------------------------------------------------------------------ 8 

Referencescited---------------------------------------------------------------- 8 

ILLUSTRATIONS 

FIGURE 1. ~ap of Colorado showing major basins and uplifts, Wilderness Lands, and oil and gas potential in 

Page 

Wilderness Lands ------------------------------------------------------------------------- E2 

2. Map of Colorado showing boundaries of USGS petroleum provinces used by Dolton and others (1981, p. 75) 

and location of Wilderness Lands with designated petroleum potential ------------------------------ 3 

3. Map of Colorado showing outlines of Wilderness Lands and oil and gas fields from. U.S. Geological Survey and 

Colorado Geological Survey (1977) ------------------------------------------------------------- 4 

III 

PETROLEUM POTENTIAL OF WILDERNESS LANDS IN THE WESTERN UNITED STATES 

Petroleum Potential of Wilderness Lands in Colorado 

By Charles W. Spencer 

ABSTRACT 

A comprehensive review of the geology of 4,501,128 acres of 

Wilderness Lands in Colorado has been made to assess the petroleum potential of these lands. The petroleum potential can 

be summarized by acreage as follows: high potential, 140.2 

thousand acres; medium potential, 94.8 thousand acres;low potential 819.4 thousand acres; zero potential, 2,445.3 thousand 

acres; and unknown potential, 1,001.4 thousand acres. Lands 

classified as having unknown potential are in areas where 

geologic conditions are such that the potential cannot reasonably be predicted and therefore may or may not contain oil and 

gas accumulations. The Wilderness Lands rated as having high 

potential are adjacent to producing fields or on trend with production. Those wilderness tracts reported to have zero potential mostly comprise areas with exposed Precambrian rocks or 

very thin sedimentary cover with no potential for petroleum 

occurrence. 

INTRODUCTION 

A review has been made of the oil and gas potential of 4. 5 million acres of various categories of 

Wilderness Lands in Colorado. The types of Wilderness Lands are shown on a map of Colorado 

prepared by the U.S. Bureau of Land Management (1981). These Colorado Wilderness Lands include: USFS and NPS Designated Wilderness, 

NPS Administratively Endorsed as Suitable (prior 

to 1981), BLM and USFS Further Planning or 

Study Areas, and BLM Lands Under Appeal. 

The tectonic elements of Colorado and other 

Rocky Mountain States are identified and discussed by Grose (1972). The general surface geology of Colorado is shown by Tweto (1979). Structure contours on the top of the Precambrian in 

E1 

Colorado are shown by MacLachlan and Kleinkopf 

(1969). The general stratigraphy of Colorado and 

other Rocky Mountain States is discussed in Mallory (1972). The State of Colorado is bisected by 

the north-south trending Front Range uplift and 

adjacent Sangre de Cristo uplift. The cores of the 

Front 'Range uplift and many other mountain uplifts are predominantly Precambrian igneous and 

metamorphic rocks. Many of the Wilderness 

Lands are situated in these areas of exposed Precambrian rocks and therefore have zero potential 

for oil and gas. In a few localities Precambrian 

rocks are thrust over Phanerozoic (Cambrian and 

younger) rocks with low or unknown oil and gas 

potential. 

Figure 1 is a map showing the location of Wilderness Lands in Colorado and selected basins and 

uplifts. These boundaries are based on geologic 

features and are slightly different from the province boundaries used by Dolton and others (1981) 

shown in figure 2, which are mostly placed along 

county lines in Colorado. 

Through 1981, oil and gas fields in Colorado had 

produced 1,328 million barrels (MMB) of oil and 

4,843 billion cubic feet (BCF) of gas (Colo. Oil and 

Gas Coils. Comm., 1981). Oil- and gas-producing 

reservoirs range in age from Mississippian to Tertiary. Most of the oil production comes from rocks 

of Permian-Pennsylvanian, Jurassic, Cretaceous, 

and Tertiary age. Most of the gas production is 

from Permian-Pennsylvanian, Cretaceous, and 

Tertiary sandstones. A map prepared by the U.S. 
38° 

0 

I 

0 I 

50 

105° 

50 100 MILES I I I I 100 KILOMETERS 

104° 103° 

EXPLANATION 

RELATIVE OIL AND GAS POTENTIAL 

-HIGH 

m MEDIUM 

ITITIIIill LOW 

D ZERO 

~UNKNOWN 

WILDERNESS LANDS REFERRED 

TO IN THIS REPORT 

1 Big Blue 

2 La Garita 

3 Weminuche 

4 South San Juan 

5 Lizard Head 

6 Raggeds 

7 West Elk 

8 Maroon Bells-Snowmass 

9 Flat Tops 

10 Eagles Nest 

11 Never Summer 

12 D1 nosaur Nat1onal Park 

FIGURE 1.-Map of Colorado showing major basins and uplifts, Wilderness Lands, and oil and gas potential in Wilderness Lands. 

Geological Survey and Colorado Geological Survey 

(1977) shows the more significant oil and gas fields 

and the age of the producing formations. Figure 

3 shows the location of Colorado oil and gas fields. 

The geologic and engineering details of many of 

these fields are shown in Crouch (1982),and Fassett (1978). 

ACKNOWLEDGMENTS 

The many reports on the surface geology and 

mineral potential of Colorado Wilderness and 

Primitive Areas published by my U.S. Geological 

Survey colleagues were a valuable source of information to supplement information from wells 

drilled for oil and gas. I would particularly like to 

thank Ogden Tweto for his identification of areas 

where Precambrian rocks are thrust over potentially oil- and gas-productive rocks. His extensive 

knowledge of the geology of Colorado was also 

E2 

helpful in attempting to predict the presence or 

absence of oil and gas in areas covered by Tertiary volcanic rocks and volcaniclastic sediments. 

METHODS OF EVALUATION 

This evaluation is based on published and unpublished data. It takes into consideration the distribution and types of oil and gas accumulations in 

both producing and abandoned fields. The analysis 

is heavily weighted toward the known or interpreted distribution of reservoir rocks, hydrocarbon 

source beds, geologic history, and stratigraphic 

and structural style favorable for oil and gas accumulations in Colorado and adjacent States. 

Hydrocarbon accumulations require four critical 

factors: (1) reservoir (porous) rocks, (2) hydrocarbon (organic-rich) source beds, (3) a relatively impermeable seal or barrier to prevent upward and 

lateral migration of hydrocarbons, and (4) favor-
40° 

39• 

107° 

SOUTHWESTERN 

WYOMING BASINS 

UINTA-PICEANCEEAGLE BASINS 

104° 103° 

EXPLANATION 

RELATIVE OIL AND GAS POTENTIAL 

• HIGH 

~MEDIUM 

• LOW 

D ZERO 

~UNKNOWN 

DENVER BASIN 

ANADARKO 

RATON BASIN- BASIN 

SIERRA GRANDE UPLIFT 

0 50 100 MILES 

50 100 KILOMETERS 

FIGURE 2.-Map of Colorado showing boundaries of USGS petroleum provinces used by Dolton and others (1981, p. 75) and location of Wilderness Lands with designated petroleum potential. 

able thermal history. It is generally accepted that 

heat and time are required to thermochemically 

alter organic material (kerogen) and yield oil and 

(or) gas. Shallow, low-temperature gas of biologic 

origin is not believed to have any significant resource potential within any of the Wilderness 

Lands in Colorado. 

Two main types of hydrocarbon traps are (1) 

structural traps, usually related to tectonic movement, including, but not limited to, folds (anticlines) and faults or combinations of folds and 

faults; and (2) stratigraphic traps, those traps 

formed by an updip change of porous sandstone or 

carbonate into impermeable shale or evaporites. 

In many fields the hydrocarbon trap is a combination of both structure and stratigraphy. 

The relative ratings of hydrocarbon potential 

used in this evaluation are as follows: 

E3 

High potential.-Geologic environment highly 

favorable for occurrence of oil and gas accumulations. Area is near or on trend with existing production from structural and (or) stratigraphic 

traps. 

Medium potential.-Geologic environment 

favorable for the discovery of oil and gas fields. 

Contains known reservoir rocks and hydrocarbon 

source beds. Includes some areas of sparse subsurface control or areas where known or expected 

field size will be small. 

Low potential.-Geologic environment interpreted to have low potential for oil and gas. Includes 

areas of poor or unknown hydrocarbon-source bed 

richness and reservoir quality. Generally includes 

areas of sparse or no well control and (or) expected thin section of sedimentary rocks. 
.. . . ··:. . . '·, '. ,_, .,\-: ··'· t 

.. ~ , 

··' .t ' 

7"~··:.,, '••' . ... -·,. ,,,, . ~ . . . . ....... . ow . , .·,t· .• a• ~· .i ••• • • •• .,,,, 

. ·1. '· ··~.· ~-~ .. ·: ".; f .:- "~-· ,J, ,; .. : . ,,,J,._,. 

, ... .,: .. ~' .... • r'l ••'•,.J;• •:J ~;;, ••. , • , •c • •• • •. , II Jll . 

..... .. "'·· \ .. . 

, 

• 

. •. , •. , - . ~ 

. . 

. . " . .. 

' 

0 50 100 MiLES 

0 50 100 KILOMETERS 

FIGURE 3.-Map of Colorado showing outlines of Wilderness Lands and oil and gas fields (shown in black) from U.S. Geological 

Survey and ColoFado Geological Survey (1977). This map is an example of a machine-plotted map produced from the digitized 

wilderness data from a 1:1,000,000-scale map (U.S. Bureau of Land Management, 1981). 

Zero potential.-Mostly comprises areas with 

exposed Precambrian rocks or very thin sedimentary cover with no potential for occurrence of 

sealed structural or stratigraphic traps. 

Unknown potential.-Generally includes areas 

of no well control where Tertiary volcanic intrusions and volcaniclastic rocks are present on the 

surface. This cover, plus lack of subsurface well 

and geophysical control, makes prediction of hydrocarbon potential impossible. Includes some 

areas where Precambrian igneous and metamorphic rocks are thrust over Phanerozoic sedimentary rocks of unknown potential. Lack of control 

does not mean that no oil and gas potential exists 

but only that the potential can not reasonably be 

determined with present data. 

E4 

PETROLEUM PROVINCE POTENTIALS 

Province names are those used in Dolton and 

others (1981). The boundaries of these provinces 

are shown in figure 2. Selected geologic basins and 

uplifts of Colorado are shown in figure 1. The Wilderness Lands of Colorado are shown in the Miscellaneous Investigations Series Map I-1539 (in 

press) along with the qualitative petroleum potential assessments and other basic information. 

RATON BASIN-SIERRA GRANDE UPLIFT 

PROVINCE 

The Raton basin contains prospective Pennsylvanian sandstone, arkose and limestone, Triassic 

and Jurassic limestone and sandstone, and Cre-
tacettus and Tertiary sandstone and fractured 

shale. The Raton basin has a few small fields but 

to date does not have any large oil and gas fields; 

however, significant carbon dioxide accumulations 

have been discovered in Cretaceous sandstones. 

Carbon dioxide is used to recover oil from depleted reservoirs and reservoirs containing lowgravity (heavy) oil. Though drilling is sparse in 

the basin, many of the dry holes have yielded oil 

and gas shows and noncommercial volumes of hydrocarbons from Cretaceous rocks. To the east of 

the basin, the sedimentary rocks are thin and hydrocarbon source beds are generally not present. 

Wilderness Lands within this province have low 

or zero potential. Wilderness Land with low potential in the northern part of the province is located on and adjacent to the Sangre de Cristo uplift. Potential is low here because the Pennsylvanian strata present have poor reservoir porosity, 

hydrocarbon source beds are generally thin, and 

Cretaceous strata are absent. Some of the lands 

on the Sangre de Cristo uplift have zero potential 

because of extensive exposures of Precambrian 

rocks. 

To the south, the wilderness tract designated 

by BLM as 2-271 (U.S. Bureau of Land Management, 1981) is on and adjacent to the Spanish 

Peaks Tertiary igneous intrusions. Here, Cretaceous age rocks contain organic-rich shales, coals, 

and sandstone reservoir rocks but have low potential because of possible vertical leakage of hydrocarbons along the contact between the intrusives 

and the sedimentary rocks. Igneous intrusions per 

se are not particularly detrimental but in this locality the concentration of stocks and dikes is such 

that they downgrade the oil and gas potential. The 

main cores of the Spanish Peaks ingeous stocks 

have zero potential. 

ALBUQUERQUE-SANTA FE-SAN LUIS 

RIFT BASINS PROVINCE 

The San Luis basin part of this province (fig. 1) 

has no oil and gas production. Only a few oil and 

gas test wells have been drilled in the basin; however, many water wells producing from Tertiary 

and Quaternary sediments have had gas shows. 

This methane gas was generated by the metabolic 

processes of microorganisms (D. D. Rice, oral 

commun., 1982). The subsurface geology of this 

basin is very poorly known owing to lack of drilling. The few wells that have been drilled indicate 

that the basin is filled with a great thickness of 

E5 

upper Tertiary to Quaternary nonmarine deposits. 

Wilderness Lands have low and unknown potential within the San Luis basin. 

SAN JUAN BASIN PROVINCE 

The northern part of the San Juan basin province includes Wilderness Lands in the San Juan 

uplift area (fig. 1). The Tertiary volcanic complex 

of the San Juan uplift is situated west of the San 

Luis basin, north of the San Juan basin, and east 

of the Paradox basin. A small amount of oil production from Cretaceous sandstone and fractured 

shale has been found on the structural high between the San Luis and San Juan basins (Ryder, 

1977a). Cumulative production from fields on this 

high area is about 6.3 MMB of oil through 1981. 

Wilderness Lands in the area in and adjacent to 

the San Juan uplift have been studied for their 

mineral potential (Fisher and others, 1968; Steven 

and others, 1969; Steven and others, 1977; Ryder, 

1977b). Wilderness Lands on the north flank of the 

San Juan uplift in the Big Blue to La Garita Wilderness areas are rated as having unknown potential owing to thick Tertiary volcanic cover and lack 

of well or other subsurface control. However, Steven and Bieniewski (1977, p. 37) note that the oil 

and gas potential in the La Garita Wilderness is 

"slight at best." This large group of tracts with 

unknown potential is actually located at the 

boundaries of four provinces, as used by Dolton 

and others (1981) and shown in figure 2. These 

provinces are the San Juan basin, AlbuquerqueSanta Fe-San Luis rift basins, Paradox basin, and 

Uinta-Piceance-Eagle basins. The western part of 

the W eminuche Wilderness has zero potential because of exposed Precambrian rocks. The eastern 

part of this wilderness tract has low and unknown 

potential because of a thick cover of Tertiary volcanic and volcaniclastic rocks. Prospective Cretaceous sedimentary rocks are interpreted to be 

present in the area with low potential. The South 

San Juan Wilderness and adjacent lands were discussed by Ryder (1977a; 1977b) and are rated as 

medium and low potential on the basis of the 

known or interpreted presence of prospective Cretaceous strata. 

PARADOX BASIN PROVINCE 

The Paradox basin (including the Four Corners 

Platform of Grose, 1972) of southeast Utah and 

southwest Colorado has many oil and gas fields 

(Fassett, 1978; Crouch, 1982). Producing reser-
voirs range in age from Devonian to Cretaceous. 

Most of the production is in the Utah portion of 

the basin. In Colorado most of the production 

comes from Pennsylvanian and Mississippian carbonate reservoirs, and Permian and Cretaceous 

sandstones. Donaldson and MacMillan (1980) list 

cumulative production and producing formations 

for the principal fields of the Colorado part of the 

Paradox basin. These principal fields produced 

8,397,175 barrels of oil and 170.7 BCF of gas 

through 1978. 

The potential of wilderness tracts in the Colorado part of the basin range from low on the 

north and east to high in the extreme southwest 

part of the State. In the north and east, Pennsylvanian source beds and carbonate reservoir rocks 

are thinner and of generally lower porosity. In the 

east, the Lizard Head Wilderness has low potential owing to the lack of nearby production and the 

presence of Tertiary igneous stocks; however, 

mineable coal beds in the Cretaceous Dakota 

Sandstone are present (Bromfield and Williams, 

1972) and these coals could have yielded gas to adiacent sandstone reservoirs. Oil shows have been 

noted in two outcrop areas within 10 miles of the 

Mount Wilson Primitive Area (approximate area 

of Lizard Head Wilderness) by Bromfield and Williams (1972, p. A60). They note that this area 

could contain oil and gas ·accumulations but that 

the overall potential is poor. There is probably 

zero potential in the igneous stocks. Subsurface 

log and test data in the Colorado part of the 

Paradox basin indicate that the Pennsylvanian 

reservoir and source bed quality increases to the 

south and west. There are also oil and gas fields 

in this area. Hence wilderness tracts in this area 

have medium to high potential. 

UINTA-PICEANCE-EAGLE BASINS PROVINCE 

The Piceance basin of Colorado has many producing gas fields. The principal fields are listed in 

Donaldson and MacMillan (1980). They note that 

the principal fields in this basin produced 598 

MMB of oil and 1,170.9 BCF of gas through 1978. 

Most of the gas was produced from Cretaceous 

and Tertiary sandstones and most of the oil came 

from the giant Rangely field that produces from 

the Permian-Pennsylvanian Weber Sandstone and 

fractured Upper Cretaceous Mancos Shale. Tracts 

in the main part of this basin have high potential 

because they are on trend with or adjacent to 

existing production. 

E6 

Wilderness tracts in the south, on the northeast 

flank of the Uncompahgre uplift, were rated as 

having low potential owing to the thinner sequence of prospective Paleozoic and Cretaceous 

reservoir rocks in this area. Tracts higher on the 

Uncomphagre uplift have zero potential owing to 

exposed Precambrian rock or thin sedimentary 

strata. 

In the southeast part of the basin the Raggeds 

and West Elk Wilderness Areas were rated as 

having low potential or unknown potential. Cretaceous source and reservoir rocks are present but 

have been intruded to varying degrees by Tertiary intrusive igneous rocks. Meeves and 

Bieniewski (1977) studied the mineral potential of 

the West Elk Wilderness and noted gas shows and 

minor oil shows in coreholes drilled for coal in an 

area between the Raggeds and West Elk Wilderness Areas. 

Insufficient subsurface data are available to 

evaluate the oil and gas potential of the Maroon 

Bells-Snowmass Wilderness north of the Raggeds 

Wilderness Area. Therefore, the area is rated as 

having unknown potential. This is an uplifted, 

mountainous area with extensive exposures of 

complexly folded and faulted Paleozoic and 

Mesozoic sedimentary rocks intruded by Tertiary 

igneous rocks. If any potential exists, it is fairly 

low and probably would be gas associated with 

Cretaceous coal beds. 

Some areas of low potential were identified in 

the Dotsero basin of Ogden Tweto (oral commun., 

1983), formerly called the Eagle basin by others, 

and southeast part of the Sand Wash basin (fig. 1). 

Only a few wells have been drilled in this structurally complex area. There is no production in 

the Dotsero basin. The few wells that have been 

drilled indicate that potential exists for small production from Pennsylvanian and Cretaceous reservoirs (where present). Mallory and others (1966) 

studied the Flat Tops Wilderness Area and noted 

that the oil potential was poor in the southern 

part of the wilderness. This part of the Flat Tops 

area has been rated as having either unknown or 

zero potential. The north edge of the Flat Tops 

Wilderness was rated as having low potential for 

production from Mesozoic and Paleozoic reservoirs. 

Tweto and others (1970) studied the mineral potential of the Eagles Nest Primitive Area and 

noted that the Precambrian outcrop areas had 

zero potential for oil and gas but that a small area 

of exposed Cretaceous through Pennsylvanian age 
rocks 'l>n the west side of the area had some remote chance of containing oil and gas but that 

none is known to exist (Tweto and others 1970, p. 

C96). This area is located on the east side of the 

Dotsero basin and is rated as having low potential 

for oil and gas in Pennsylvanian reservoirs. 

PARK BASINS PROVINCE 

The North and Middle Park basin is an intermontane basin almost completely surrounded by 

uplifts composed of Precambrian rocks. This basin 

has produced 12.4 MMB of oil and 658 BCF of gas 

through 1981 (Colo. Oil and Gas Cons. Comm., 

1981). Most of the gas has a high content of carbon 

dioxide and is nonflammable. The producing rocks 

are of Cretaceous and Jurassic age. Most of the 

Wilderness Lands in the Precambrian outcrop 

areas surrounding the basin have zero oil and gas 

potential; however, a small area on the east flank 

of this basin is an area (Never Summer Wilderness) where Precambrian rocks have been 

thrust over Tertiary, Cretaceous, Jurassic, and 

Triassic rocks (Pearson and others, 1981). This 

area is rated as having unknown potential. Pearson and others (1981, p. 54) interpreted the Never 

Summer Wilderness to have poor petroleum potential because of strong thermal metamorphism 

(heating); however, methane gas is thermally very 

stable and small amounts of flammable gas might 

be present. 

Tract 010-155 (U.S. Bureau of Land Management, 1981), in the south-central part of the basin, 

has unknown potential. Here Tertiary volcanic 

rocks are present on the surface (Tweto, 1979) and 

the presence or absence of prospective Cretaceous 

and Jurassic rocks under this cover can not be determined. Several wells drilled north and east of 

this tract have tested gas from Cretaceous reservoirs. The North and Middle Park basin is connected to the South Park basin by a narrow intermontane trough. Parts of wilderness tracts on the 

west side of the trough and the west side of South 

Park basin have low potential for oil and gas. Cretaceous and Jurassic rocks with low oil and gas potential are also present under the east side of the 

Eagles Nest Wilderness bordering the west side 

of the trough. A small part of the wilderness area 

on the west side of the South Park basin has low 

potential for oil and gas in Pennsylvanian rocks. 

Unknown potential is given to U.S. Forest Service Wilderness Study Lands on the east side of 

the structural trough connecting the Park basins. 

Cretaceous and Precambrian rocks are exposed in 

this area (Tweto, 1979). The Precambrian outcrop 

area with unknown potential has Precambrian 

rocks thrust over prospective Cretaceous and 

Jurassic sedimentary rocks (Ogden Tweto, oral 

commun., 1983). Gries (1983) shows the east edge 

of this trough to be bounded by an east-to-west directed thrust fault. 

SOUTHWESTERN WYOMING BASINS PROVINCE 

The Southwestern Wyoming Basins province extends into northwest Colorado (fig. 2). In Colorado 

most of this area is called the Sand Wash basin 

(Grose, 1972). Wilderness Lands located in the 

southwest corner of this province (fig. 2) are located on the Skull Creek anticline and are rated as 

having low potential for oil and gas. These lands 

are geologically on the edge of the Piceance basin. 

The tracts are about 12 miles north of the giant 

Rangely oil field which produces oil chiefly from 

the Permian-Pennsylvanian Weber Sandstone and 

some oil from fractured Cretaceous shales. The 

tracts are mostly situated on the large, east-west 

trending Skull Creek anticline. The Weber 

Sandstone, which is the producing reservoir at 

Rangely, is exposed at the eastern end 

of the anticline, thereby greatly reducing the hydrocarbon potential of these tracts. However, Ball 

Associates (1965) describe scattered tar or asphaltic impregnation in Permian-Pennsylvanian, Triassic, and Jurassic rocks in the area. They note that 

"most of the accumulations are on the north and 

northeast flanks of the Skull Creek anticline and 

along the Wolf Creek fault * * *." (Ball Associates, 1965, p. 91). Several wells have been 

drilled without success on the anticline; however, 

one of the wells had oil shows in samples of 

Paleozoic carbonate rocks. The lack of success of 

the wells drilled on structure and the partial exposure of the reservoirs that are productive at 

Rangely field warrant a rating of no higher than 

low potential. 

National Park Service Wilderness Lands in Dinosaur National Park lie north of the Skull Creek 

tracts. Much of these lands have unknown potential. Most of the area with unknown potential is a 

structurally high area that has extensive exposures of Pennsylvanian and Permian sandstone, 

shale, and carbonates. Several faults cut through 

the area and the possibilities for trapping hydrocarbons seem poor. However, Ball Associates 

(1965, p. 92) did report one small asphalt-impregE7 
nated deposit in the Weber Sandstone in the unknown potential area. 

One small tract in the extreme northwest 

corner of Colorado is located at the east end of, 

and on the north flank of the Uinta uplift (Grose, 

1972). This is an area where Precambrian 

sedimentary rocks of the Uinta Mountain Group 

are exposed. A well drilled just northeast of this 

tract penetrated 7,100 ft (2,164 m) of overthrust 

Precambrian sediments and then entered Upper 

Cretaceous Mancos Shale (Gries, 1983). The well 

was then abandoned in the Weber at 13,780 ft 

(4,200 m). A few oil and gas shows were reported 

(Gries, 1983). The possibility exists that Cretaceous and older rocks may be present under this 

tract with unknown potential. 

SUMMARY 

Of the 4,501,128 acres of Wilderness Lands in 

Colorado included in this assessment the petroleum potential can be summarized by acreage as 

follows: high potential, 140.2 thousand acres; 

medium potential, 94.8 thousand acres; low 

potential, 819.4 thousand acres; zero potential 

2,445.3 thousand acres; and unknown potential 

1,001.4 thousand acres. The petroleum potential 

by acreage of all Wilderness Land categories in 

the Western United States is shown in this circular by B. M. Miller in. table 1, chapter P. 

REFERENCES CITED 

Ball Associates, Ltd., 1965, Surface and shallow oil-impregnated rocks and shallow oil fields in the United States: 

U.S. Bureau of Mines Monograph 12, 375 p. 

Bromfield, C. S., and Williams, F. E., 1972, Mine:-al resources 

of the Wilson Mountains Primitive Area, Colorado: U.S. 

Geological Survey Bulletin 1353-A, 79 p. 

Colorado Oil and Gas Conservation Commission, 1981, 1981 oil 

and gas statistics: Colorado Oil and Gas Conservation 

Commission, Denver, 241 p. 

Crouch, M. C., 1982, Oil and gas fields of Colorado-Nebraska 

and adjacent areas: Rocky Mountain Association of 

Geologists, 791 p. 

Dolton, G. L., Carlson, K. H., Charpentier, R. R., Coury, A. 

B., Crovelli, R. A., Frezon, S. E., Khan, A. S., Lister, J. 

H., McMullin, R. H., Pike, R. S., Powers, R. B., Scott, 

E. W., and Varnes, K. L., 1981, Estimates of undiscovered recoverable conventional resources of oil and gas in 

the United States: U.S. Geological Survey Circular 860, 87 

p. 

Donaldson, J. C., and MacMillan, Logan, 1980, Oil and gas: 

history of development and principal fields in Colorado, in 

Colorado Geology: Rocky Mountain Association of 

Geologists, p. 175--189. 

Fassett, J. E., ed., 1978, Oil and gas fields of the Four Corners 

area: Four Corners Geological Society, 727 p. 

E8 

Fischer, R. P., Luedke, R. G., Sheridan, M. J., jUld Ra.;;}bi, R. 

G., 1968, Mineral resources of the Uncompahgre Primitive 

Area, Colorado: U.S. Geological Survey Bulletin 1261-C, 

91 p. 

Gries, Robbie, 1983, Oil and gas prospecting beneath Precambrian of foreland thrust plates in Rocky Mountains: American Association of Petroleum Geologists, v. 67, no. 1, p. 1-

28. 

Grose, L. T., 1972, Tectonics, in Mallory, W. W., ed., Geologic 

atlas of the Rocky Mountain region: Rocky Mountain Association of Geologists, p. 35--44. 

MacLachlan, J. C., and Kleinkopf, M. D., 1969, Configuration 

of the crystalline basement rocks of Colorado: Rocky 

Mountain Association of Geologists, scale 1:500,000. 

Mallory, W. W., ed., 1972, Geologic Atlas of the Rocky Mountain Region: Rocky Mountain Association of Geologists, 

331 p. 

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

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

Flat Tops Primitive Area, Colorado: U.S. Geological Survey Bulletin 1230-C, 30 p. 

Meeves, H. C., and Bieniewski, C. L., 1977, Mines, prospects, 

and mineralized areas of the West Elk Wilderness Study 

Area, Delta and Gunnison Counties, Colorado, Chapter D, 

in Mineral Resources of the West Elk Wilderness and vicinity, Delta and Gunnison Counties, Colorado: U.S. 

Geological Survey Open-File Report 77-751, p. 78-111. 

Pearson, R. C., Braddock, W. A., Flanigan, V. J., and Patten, 

L. L., 1981, Mineral resources of the Comanche-Big 

South, Neota-Flat Top, and Never Summer Wilderness 

Study Areas, north-central Colorado: U.S. Geological Survey Open-File Report 81--578, 73 p. 

Ryder, R. T., 1977a, Hydrocarbon potential of the Archuleta 

anticlinorium, Brazos uplift, Chama basin: The Oil and Gas 

Journal, Dec. 5, 1977, p. 163-170. 

--1977b, Oil and gas potential of the Chama-southern San 

Juan Mountains Wilderness Study Area, MineraJ, Rio 

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