Chapter P

Geology and Resource Assessment of the 

Middle and Upper Coal Groups in the 

Yampa Coal Field, Northwestern Colorado

By Edward A. Johnson,1 Laura N.R. Roberts,1

Michael E. Brownfield,1 and Tracey J. Mercier2

U.S. Geological Survey Professional Paper 1625–B*

U.S. Department of the Interior

U.S. Geological Survey

Chapter P of

Geologic Assessment of Coal in the Colorado Plateau:

Arizona, Colorado, New Mexico, and Utah

Edited by M.A. Kirschbaum, L.N.R. Roberts, and L.R.H. Biewick

1 U.S. Geological Survey, Denver, Colorado 80225

2

 U.S. Geological Survey contract employee, Denver, Colorado 80225

* This report, although in the USGS Professional Paper series,

is available only on CD-ROM and is not available separately

National Coal

Resource

Assessment

Click here to return to Disc 1 

Volume Table of Contents
Contents

Abstract........................................................................................................................................................P1

Introduction ................................................................................................................................................... 1

Purpose and Scope ............................................................................................................................. 1

Location................................................................................................................................................. 2

Previous Geologic Studies ................................................................................................................. 2

Previous and Current Mining Activity .............................................................................................. 2

Methods Used in the Assessment .................................................................................................... 6

Lithologic Data ............................................................................................................................ 6

Stratigraphic Data ...................................................................................................................... 6

Cartographic Data ...................................................................................................................... 6

Acknowledgments............................................................................................................................... 8

Geologic Setting............................................................................................................................................ 8

Cretaceous Paleogeography ............................................................................................................. 8

General Stratigraphy of Cretaceous Sedimentary Rocks in Northwestern Colorado ............. 8

Mesaverde Group in the Yampa Coal Field ..................................................................................... 8

Detailed Stratigraphy of the Upper Cretaceous (Upper Campanian) Williams 

Fork Formation in the Yampa Coal Field............................................................................ 11

Trout Creek Sandstone Member (Iles Formation) ............................................................... 14

Yampa Bed ................................................................................................................................. 14

Sub-Twentymile Sandstone .................................................................................................... 14

Twentymile Sandstone Member of the Williams Fork Formation..................................... 14

Big White Sandstone ............................................................................................................... 15

Three White Sandstones......................................................................................................... 15

Depositional Environments Represented in the Williams Fork Formation ............................... 16

Offshore Marine Mudrock....................................................................................................... 16

Nearshore Marine Sandstone................................................................................................ 16

Nonmarine Deposits................................................................................................................. 16

Brief History of the Deposition of the Mesaverde Group in the Yampa Coal Field ................. 17

Post-Mancos Shale Regional Cretaceous Stratigraphy in Northwestern Colorado.............. 17

Post-Cretaceous Deformational History of Northwestern Colorado ........................................ 19

Structural Features of the Yampa Coal Field................................................................................. 19

Coal Assessment ........................................................................................................................................ 21 

Coal Distribution................................................................................................................................. 21

A Coal Zone................................................................................................................................ 23

Barren Interval A ...................................................................................................................... 25

B Coal Zone................................................................................................................................ 25

Barren Interval B ...................................................................................................................... 25

C Coal Zone................................................................................................................................ 27

Barren Interval C....................................................................................................................... 27
D Coal Zone................................................................................................................................ 27

Coal Quality......................................................................................................................................... 29

Coal Resources .................................................................................................................................. 29

A Coal Zone................................................................................................................................ 31

B Coal Zone................................................................................................................................ 32

C Coal Zone................................................................................................................................ 32

D Coal Zone................................................................................................................................ 32

Restrictions to Coal Availability....................................................................................................... 32

Summary of Coal Resources............................................................................................................ 40

Selected References.................................................................................................................................. 42

Appendix 1—Metric Conversion Factors ............................................................................................... 47

Appendix 2—Information on Publicly Available Exploration Drill Holes Used in this Report........ 48

Appendix 3—Estimated Remaining Coal Resources in the A Coal Zone,

Williams Fork Formation, Yampa Coal Field .............................................................................. 52

Appendix 4—Estimated Remaining Coal Resources in the B Coal Zone,

Williams Fork Formation, Yampa Coal Field .............................................................................. 55

Appendix 5—Estimated Remaining Coal Resources in the C Coal Zone,

Williams Fork Formation, Yampa Coal Field .............................................................................. 58

Appendix 6—Estimated Remaining Coal Resources in the D Coal Zone,

Williams Fork Formation, Yampa Coal Field .............................................................................. 61

Appendix 7—ArcView Project for the Yampa Coal Field, Northwestern Colorado

[The digital fi les used for the coal resource assessment of the Yampa coal

fi eld are presented as views in the ArcView project. The ArcView project 

and the digital fi les are stored on both discs of this CD-ROM set—Appendix 7 

of chapter P resides on both discs. Persons who do not have ArcView 3.1 may 

query the data by means of the ArcView Data Publisher on disc 1. Persons who 

do have ArcView 3.1 may utilize the full functionality of the software by accessing 

the data that reside on disc 2. An explanation of the ArcView project and data library

—and how to get started using the software—is given by Biewick and Mercier 

(chap. D, this CD-ROM). Metadata for all digital fi les are also accessible through 

the ArcView project]

Appendix 8—Stratigraphic Database for the Yampa Coal Field, Northwestern Colorado

[Location, lithologic, and stratigraphic data are available in ASCII format, 

DBF, and Excel spreadsheets on disc 2 of this CD-ROM set]

Plate

 1. Subsurface correlations of coal and related rocks in the middle and upper 

coal groups of the Upper Cretaceous Williams Fork Formation in the 

Yampa coal field, northwestern Colorado ............................................................................P65

 Figure A. Index map showing location of cross sections A-A′, B-B′, 

and C-C′, and drill hole H-36-H

 Figure B. Coal correlations of the upper coal group along cross section A-A′

 Figure C. Coal correlations of the middle coal group along cross section B-B′
 Figure D. Coal correlations of the middle coal group along cross section C-C′

 Figure E. Lithologic interpretation of geophysical log of drill hole H-36-H

Figures

 1. Location of the Yampa coal field, Moffat, Rio Blanco, and 

Routt Counties, Colorado...........................................................................................................P3

 2. Map showing Federal and non-Federal surface ownership in 

the Yampa coal field..................................................................................................................... 4

 3. Index map of public drill holes used in the assessment of the Yampa coal field .............. 7

 4. Index map of 7.5′ quadrangle maps covering the Yampa coal field..................................... 9

 5. Paleogeographic map of the central part of North America 

during the late Campanian........................................................................................................ 10

 6. Generalized cross section of the Mesaverde Group depositional environments 

in northwestern Colorado ......................................................................................................... 12

 7. Stratigraphic column of the Williams Fork Formation in the Yampa coal field ................ 13

 8. Regional correlation of the Mesaverde Group and younger Cretaceous 

formations in northwestern Colorado ..................................................................................... 18

 9. Structure contour map of the Trout Creek Sandstone Member of the 

Iles Formation in the Yampa coal field .................................................................................... 20

 10. Geologic map of the Yampa coal field..................................................................................... 22

 11. Isopach map of net coal in beds equal to or greater than 1.2 ft in the A coal zone........ 24

 12. Isopach map of net coal in beds equal to or greater than 1.2 ft in the B coal zone........ 26

 13. Isopach map of net coal in beds equal to or greater than 1.2 ft in the C coal zone ........ 28

 14. Isopach map of net coal in beds equal to or greater than 1.2 ft in the D coal zone........ 30

 15. Isopach map of overburden to the base of the A coal zone ............................................... 33

 16. Map showing net coal in thickness categories for the B coal zone.................................. 34

 17. Isopach map of overburden to the base of the B coal zone ............................................... 35

 18. Map showing net coal in thickness categories for the C coal zone.................................. 36

 19. Isopach map of overburden to the base of the C coal zone................................................ 37

 20. Map showing net coal in thickness categories for the D coal zone.................................. 38

 21. Isopach map of overburden to the base of the D coal zone ............................................... 39

 22. Map showing Federal and non-Federal coal ownership in the Yampa coal field ........... 41

Tables

 1. List of CRO-CDP quadrangle maps for the Yampa coal field...............................................P5

 2. U.S. Geological Survey Open-File Reports containing the bore-hole 

geophysical logs of coal exploration drill holes drilled by the 

U.S. Geological Survey in the Yampa coal field....................................................................... 5
Abstract

The Yampa coal fi eld is located in northwestern Colorado 

and covers about 520 mi2 in parts of Moffat, Routt, and Rio 

Blanco Counties. Most of the coal is contained in the Upper 

Cretaceous Mesaverde Group. The Mesaverde is an eastwardtapering sedimentary wedge that contains a vertical succession 

of mixed marine and nonmarine rocks that were deposited 

along the western edge of the Late Cretaceous Western Interior 

Seaway in response to a constantly shifting shoreline. The 

Mesaverde is divided into two formations, the Iles in the 

lower part and the Williams Fork in the upper part. Included 

in the Iles is the Trout Creek Sandstone Member at the top 

of the formation, and included in the Williams Fork is the 

Twentymile Sandstone Member in the middle of the formation. 

Both of these sandstones are regressive shoreface deposits; 

each is transitional with an underlying interval of marine shale; 

and each is overlain by a thick interval of nonmarine rocks 

including fl uvial sandstone, overbank sandstone and mudrock, 

and carbonaceous shale and coal.

Earlier workers defi ned coal in the Iles as the lower coal 

group, coal between the Trout Creek and the Twentymile as 

the middle coal group, and coal above the Twentymile as the 

upper coal group. The emphasis in this report is placed on the 

middle and upper coal groups because most of the economic 

coal is contained in the Williams Fork. To better defi ne the 

occurrence of coal, four coal zones and three barren intervals 

are established in this report. The middle coal group contains 

the A coal zone, barren interval A, the B coal zone, and barren 

interval B, in ascending order. The upper coal group contains 

the C coal zone, barren interval C, and the D coal zone.

The A coal zone extends throughout the coal fi eld and 

contains the maximum number of coal beds and the greatest 

amount of net coal. A regionally signifi cant tonstein, the 

Yampa bed, is also present. All of the currently producing 

mines in the eastern part of the coal fi eld extract coal from 

this zone. The B coal zone is only found in the central and 

western parts of the coal fi eld and, other than supplying a few 

wagon mines, has never been an important source of coal. Also 

restricted to the central and western parts of the coal fi eld, 

the C coal zone has the least economic potential of the four 

zones. This zone contains the least number of coal beds and 

the least amount of net coal of the four coal zones. The D coal 

zone extends throughout the coal fi eld and is the second most 

economically important zone. The only currently producing 

mine in the western part of the coal fi eld extracts coal from 

this zone.

Most of the coal in the Williams Fork has an apparent 

rank of high-volatile C bituminous. Ash yield is usually less 

than 10 percent, sulfur content is usually less than 1 percent, 

and the average caloric value is about 11,500 Btu/lb.

The Williams Fork contains an estimated remaining netcoal resource of about 76 billion short tons. Coal classifi ed 

as identifi ed makes up about 46 percent of the resource with 

the remainder classifi ed as hypothetical. Most of the resource, 

about 80 percent, is contained in Moffat County. Although 

93 percent of the resource underlies private surface, about 

69 percent of the coal is owned by the Federal Government. 

Much of the coal is currently unavailable because of limits in 

mining technology, current economic conditions, or for various 

environmental reasons.

Introduction

Purpose and Scope

The assessment of coal in the Yampa coal fi eld of northwest Colorado is part of the National Coal Resource Assessment initiated by the U.S. Geological Survey (USGS) in 1994. 

The goal of the National Assessment is to describe the distribution and calculate the resource potential of coal in selected 

areas of the United States. In the Rocky Mountain region, the 

Yampa coal fi eld was selected because several large coal mines 

are currently extracting signifi cant amounts of coal, a high 

percentage of the coal is federally owned, and the potential for 

subsurface accumulations of coal gases is high. 

Geology and Resource Assessment of the

Middle and Upper Coal Groups in the 

Yampa Coal Field, Northwestern Colorado

By Edward A. Johnson, Laura N.R. Roberts, Michael E. Brownfi eld, and Tracey J. Mercier

P1
The assessment of the coal fi eld was restricted to four 

coal zones, all within the Upper Cretaceous Williams Fork 

Formation. Areas of Federal and State coal leases were 

excluded in the assessment. Because a high percentage of the 

coal is publicly owned and managed by the Federal Government, no effort was made to exclude State or privately owned 

coal from the assessment. The report includes coal correlation 

charts, maps showing selected aspects of the coal distribution, 

and calculated coal resources. The resources reported represent 

minimum values but are far in excess of what can be economically mined.

Location

The Yampa coal fi eld, covering 520 mi2, is located in 

northwest Colorado and occupies parts of Routt and Moffat 

Counties and a very small part of Rio Blanco County (fi g. 

1). U.S. Highway 40 crosses the coal fi eld on the north and 

connects the small communities of Milner and Lay, which 

more or less defi ne the east-west limits of the coal fi eld. More 

signifi cant towns in the area, both along Highway 40, are 

Steamboat Springs, just east of the coal fi eld, and Craig, in the 

western part of the coal fi eld. The coal fi eld is also crossed 

by the west-fl owing Yampa River, which is located just south 

of the highway. Elevations in the coal fi eld range from about 

6,000 ft above sea level near Lay to slightly more than 9,800 

ft at the top of Pilot Knob in the northeastern part of the coal 

fi eld.

The coal fi eld is comprised of three basic segments. Most 

of the coal is contained in a 47-mi-long, east-trending segment 

that extends from the town of Oak Creek on the east to near 

Lay on the west—this area is dominated by the Williams Fork 

Mountains. Almost all of the operating coal mines are within 

this segment. A second segment extends north for about 25 mi 

from the eastern end of the segment just described to a latitude 

about 18 mi north of the abandoned town of Mount Harris. 

Just south of Mount Harris, the segment contains an operating 

mine, but north of Mount Harris mining is hampered by steep 

structural dip. The third segment, isolated in the south-central 

part of the coal fi eld, contains a considerable amount of coal 

but no operating mines.

Most of the land surface in the coal fi eld is privately 

owned (fi g. 2). The Federal Government controls only seven 

percent of the surface, and almost all of this is administered 

by the U.S. Bureau of Land Management (BLM). The State of 

Colorado controls an even smaller percentage of the surface.

Previous Geologic Studies

Coal in northwestern Colorado was fi rst noted by Hayden 

(1877), and minor studies of the coal resources of the Yampa 

coal fi eld began appearing as early as the 1880’s. The fi rst 

notable investigation was published in the early 1900’s by 

Fenneman and Gale (1906b). Following this work, various 

reports on the coal resources were published, but two are 

particularity signifi cant. Hancock (1925) investigated the coal 

resources in the western part of the coal fi eld, and his report 

contains a geologic map at a scale of 1:62,500. Bass and others 

(1955) investigated the coal resources in the eastern part of 

the coal fi eld, and their report contains a geologic map at the 

same scale. These two publications remain the primary sources 

of information on the geology of the coal fi eld. During the 

mid-1970’s, Dames and Moore, under contract with the USGS, 

compiled a series of Coal Resource Occurrence and Coal 

Development Potential (CRO-CDP) 7.5′ quadrangle maps 

(table 1) that show all of the public surface and subsurface 

data on the coal fi eld available at the time. During the mid1970’s to early 1980’s, the USGS drilled more than 200 coal 

exploration holes in the coal fi eld, and down-hole information 

obtained from the geophysical logs of these holes was the 

primary source of data used in the coal assessment (table 

2). The Selected References section at the end of this report 

contains most of the signifi cant publications pertaining to the 

coal fi eld. A more comprehensive listing of reports published 

before 1984 is provided by Johnson and Brownfi eld (1984).

Previous and Current Mining Activity

According to Boreck and Murray (1979), 192 mines have 

operated in the Yampa coal fi eld at one time or another. 

Small wagon mines provided coal from various beds in the 

Mesaverde Group for domestic use during the second half of 

the 19th century, but larger scale mining was hampered by a 

lack of adequate transportation. Following the arrival of the 

railroad in 1909 (Campbell, 1923), signifi cant underground 

mines were established near Oak Creek and Mount Harris in 

the eastern part of the coal fi eld. Most of the coal mined near 

Oak Creek was from the Upper Cretaceous Iles Formation, a 

unit not included in this assessment. In the Mount Harris area, 

the Utah Coal Company mined coal from the Williams Fork 

Formation south of the Yampa River and the Victor-American 

Fuel Company mined coal from the formation north of the 

river. Large strip mines were later established in the eastern 

part of the coal fi eld that also extracted coal from the Williams 

Fork. The Edna mine was located about 3 mi north of Oak 

Creek, and the Energy mine was located in the southern part of 

Twentymile Park. Both of these mines have ceased operations 

and have been reclaimed.

Currently, only a few large mines operate in the coal fi eld 

(fi g. 1), and all of these extract coal from the Williams Fork. 

In the eastern part of the coal fi eld, the Foidel Creek mine 

(underground) is located in the southern part of Twentymile 

Park, and the Seneca II-W and Yoast mines (both surface), 

are located several miles southwest of Mount Harris. A fourth 

mine, the Seneca II is located several miles south of Mount 

Harris but is mined out and is about to be reclaimed. Using 

three 1-mi-long longwall mining machines, the largest such 

system in the world, the Foidel Creek mine set a monthly coal 

production world record in 1996 of just more than 1 million 

P2 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
 R. 94 W. R. 93 W. R. 92 W. R. 91 W. R. 90 W. R. 89 W. R. 88 W. 

 R. 87 W. 

ROUTT CO.

RIO BLANCO CO.

MOFFAT CO.

1

2

3 4

5

6

13

13

40

●

●

●

M

Hayden

Craig

Lay

●

Mount Harris

107 30' 

Explanation

Active coal mine

1. Eagle mines2. Trapper mine3. Seneca II-W mine4. Yoast mine5. Seneca II mine6. Foidel Creek mine

Colorado

0 5 mi

Figure 1. Location of the Yampa coal fi eld, Moffat, Rio Blanco, and Routt Counties, Colorado. The outcrop of the Mesaverde Group (shaded in gray) delineate

coal fi eld. Approximate locations of existing coal mines are shown.
Federal

Non-Federal (State and private)

Surface Ownership

T. 7 N.

R 88 W. R 87 W. 

R 91 W. R 90 W. R 89 W.

R 93 W. R 92 W.

107 30' 

0 5 

Figure 2. Federal and non-Federal land surface ownership in the Yampa coal fi eld. This outline of the coal fi eld represents the maximum resource polygon u

(see defi nition in Coal Resource section in text).
short tons (Eakins and Coates, 1998; Fiscor, 1998). In the 

western part of the coal fi eld, the Trapper mine (surface), is 

located about 5 mi south of Craig, and the Eagle No. 5 mine 

(underground) and the Eagle No. 9 mine (surface) are both 

located about 12 mi southwest of Craig. The Eagle mines are 

temporarily closed. For the year 1997, the coal fi eld produced 

10.9 million short tons of coal, accounting for about 40 percent 

of Colorado’s total coal production (Resource Data International, 1998). The cumulative coal production for the Yampa 

coal fi eld, from 1864 through 1997, is 266.19 million short 

tons (Tremain and others, 1996; Resource Data International, 

1998).

Two mine-mouth power plants produce electricity in the 

coal fi eld: the Craig station, located about 4 mi south-southwest of Craig, and the Hayden station, located about 5 mi eastsoutheast of Hayden. According to plant personnel, the Craig 

station is owned by Tri State Generation and Transmission 

Association, Inc. This three-unit power plant has a net capacity 

of 1,264 megawatts (the largest capacity in Colorado) and 

features state-of-the-art environmental controls. The fi rst unit 

was completed in 1979, the second in 1980, and the third in 

1984. Most coal burned at the plant comes from the Trapper 

mine, located about 3 mi to the south-southeast, and a small 

amount comes from the Colowyo mine, located about 18 mi 

to the southwest in the northern part of the Danforth Hills 

coal fi eld. The Hayden station is owned by Public Service of 

Colorado, Pacifi cCorp, and Salt River Project. According to 

plant personnel, this two-unit power plant has a net capacity 

of 446 megawatts. The fi rst unit was completed in 1965, and 

the second unit was completed in 1976. All of the coal burned 

at the plant comes from the Seneca II-W and Yoast mines 

and, until recently, from the Seneca II mine. The Seneca II-W 

and Yoast mines are located about 1 mi to the south, and the 

Seneca II is located about 1 mi to the southeast.

Table 1. List of Coal Resource Occurrence and Coal 

Development Potential (CRO-CDP) 7.5′ quadrangle maps 

available for the Yampa coal field. 

 Quadrangle USGS Open-File Dames and Moore reference 

 Report number (see Selected References) 

 Breeze Mountain 79-1393 1979g 

 Castor Gulch 79-820 1979n 

 Cow Creek 78-629 1978d 

 Craig 78-627 1978c 

 Dunckley 79-813 1979j 

 Hamilton 79-628 1979b 

 Hayden 79-825 1979p 

 Hayden Gulch 79-1395 1979s 

 Hooker Mountain 78-626 1978b 

 Horse Gulch 79-882 1979i 

 Juniper Hot Springs 79-881 1979h 

 Lay 79-877 1979d 

 Lay SE 79-878 1979e 

 Milner 79-815 1979l 

 Monument Butte 79-281 1979a 

 Mount Harris 79-821 1979o 

 Oak Creek 79-818 1979m 

 Pagoda 79-1394 1979n 

 Pine Ridge 79-876 1979c 

 Ralph White Lake 79-880 1979g 

 Rattlesnake Butte 79-1396 1979t 

 Rock Springs Gulch 79-876 1979f 

 Round Bottom 79-814 1979k 

 Wolf Mountain 78-624 1978a 

Table 2. U. S. Geological Survey Open-File Reports, by 7.5′

quadrangle, containing bore-hole geophysical logs of coal 

exploration drill holes used in the assessment of the Yampa coal 

field. 

 Quadrangle Author USGS Open-File 

 Report number 

 Breeze Mountain Prost (1977) OF 77-155 

 Brownfield (1978b) OF 78-365 

 Johnson and Hook (1985b) OF 85-43 

 Castor Gulch Johnson and Hook (1985b) OF 85-43 

 Cow Creek Brownfield (1978b) OF 78-365 

 Bronson (1979) OF 79-1593 

 Hamilton Meyer (1977) OF 77-118 

 Meyer (1978) OF 78-366 

 Meyer and Brown (1982) OF 82-475 

 Hayden Brownfield (1976) OF 76-817 

 Prost (1977) OF 77-155 

 Brownfield (1978b) OF 78-365 

 Johnson and Hook (1985b) OF 85-43 

 Hayden Gulch Prost (1977) OF 77-155 

 Brownfield (1978b) OF 78-365 

 Johnson and Hook (1985b) OF 85-43 

 Horse Gulch Brownfield (1976) OF 76-817 

 Johnson (1978) OF 78-229 

 Meyer (1978) OF 78-366 

 Johnson and Hook (1985a) OF 85-37 

 Johnson and Hook (1985b) OF 85-43 

 Juniper Hot Springs Johnson and Hook (1985a) OF 85-37 

 Johnson and Hook (1985b) OF 85-43 

 Lay Muller (1976) OF 76-383 

 Brownfield (1978b) OF 78-365 

 Milner Brownfield (1978b) OF 78-365 

 Monument Butte Johnson and Brown (1979) OF 79-328 

 Oak Creek Brownfield (1978b) OF 78-365 

 Pagoda Meyer (1977) OF 77-118 

 Meyer (1978) OF 78-366 

 Meyer and Brown (1982) OF 82-475 

 Rattlesnake Butte Brownfield (1978a) OF 78-364 

 Brownfield (1978b) OF 78-365 

 Stevenson (1978) OF 78-1048 

 Round Bottom Johnson (1978) OF 78-229 

 Johnson and Brown (1979) OF 79-328 

 Johnson and Hook (1985a) OF 85-37 

 Johnson and Hook (1985b) OF 85-43 

Geology and Resource Assessment of the Middle and Upper Coal Groups, Yampa Coal Field, Northwestern Colorado P5
Methods Used in the Assessment

Almost all of the basic data used in the assessment were 

derived from published geologic reports and maps and from 

information obtained from coal-exploration drilling conducted 

by the USGS. Data in this assessment are reported in customary inch-pound units because the metric system is not currently 

used by the coal industry in the United States. Readers wishing to convert measurements to the International System of 

units (SI) can use the conversion factors in Appendix 1. All 

resource values are reported in short tons. In order to assess the 

coal resources, digital fi les were created of various geologic 

and geographic information within the area. Drill-hole data 

were stored and correlated using a StratiFact (GRG Corp.) 

stratigraphic database manager. Structure data and coal-zonethickness data were obtained from the database and integrated 

with digital elevation data to digitally generate the positions 

of coal-zone outcrop lines. These outcrop lines were then 

used to defi ne the boundary of assessment polygons for the 

individual coal zones within the coal fi eld. Coal-bed-thickness 

data stored in the database were fi ltered using a computer program developed by the USGS to determine net coal bed thickness. Spatial data were stored, manipulated, and analyzed in 

a geographic information system (GIS) using ARC/INFO software (Environmental Systems Research Institute, Inc.). The 

spatial data that required gridding for the generation of structure contour and isopach maps were processed using EarthVision (Dynamic Graphics, Inc.). Contour lines generated in 

EarthVision (EV) were then converted into ARC/INFO coverages using a program called ISMARC (provided by the Illinois 

Geological Survey) and an Arc Macro Language (AML) called 

“convert-ism.” Integrating the various coverages in EV allowed 

for the characterization of coal distribution and calculation of 

coal resources within a variety of geologic and geographic 

parameters. The methodology for reporting estimated coal 

resources is from Wood and others (1983) and is described in 

detail in the Coal Resources section in this report. All products 

from this assessment are available in digital form so that GIS 

technology can be used to manipulate and display the coalresource information.

Lithologic Data

Most of the subsurface information used in the assessment came from 162 of the 225 coal exploration holes drilled 

in the Yampa coal fi eld by the USGS between 1975 and 1985 

(table 2). The bore-hole geophysical logs of these drill holes 

were provided by the Craig District Offi ce of the BLM. In 

addition, the geophysical logs of 13 oil and gas exploration 

drill holes, which are publicly available, were used in the 

assessment. The locations of all 175 public drill holes are 

shown on fi gure 3, and information about these drill holes 

is given in Appendix 2. In addition, information from 81 

proprietary coal exploration drill holes where provided by the 

Craig District Offi ce of the BLM for limited use in the assessment. Several coal companies released the geophysical logs of 

a few specifi c drill holes for use in the assessment, and nine 

of these holes appear in cross sections on plate 1. Most of the 

locations for these drill holes were determined by computer 

digitization, but a small number were determined by hand 

using a Gerber scale.

Coal could usually be identifi ed on the geophysical logs 

of coal exploration drill holes with a high degree of certainty 

because the curves for natural gamma and gamma gamma density were of good quality. Major sandstone bodies were picked 

from the curves of natural gamma, spontaneous potential, and 

single-point resistance, and a tonstein (altered volcanic ash) 

unit was picked using the single-point resistance curve. For 

a comprehensive discussion of how coal is identifi ed on geophysical logs, consult Wood and others (1983, p. 60–65). On 

the geophysical logs of oil and gas exploration drill holes, 

coal and the tonstein unit were picked using the gamma ray 

and resistivity curves, and major sandstone bodies were picked 

using the spontaneous potential and resistivity curves. No 

attempt was made to identify minor sandstone bodies or argillaceous units. Because the geophysical logs were of several 

scales and varying quality, lithologic units were measured to 

the nearest foot in order to insure uniformity. However, coal 

beds in some of the proprietary data were measured to the 

nearest tenth of a foot.

Stratigraphic Data

Regional stratigraphic cross sections of the study interval 

were constructed using public subsurface data and, in several 

cases, priority data released by coal companies (pl. 1, fi gs. 

B, C, and D) . The number of coal beds encountered by any 

single drill hole that penetrated most of the study interval 

ranges from as few as four on the east side of the Yampa coal 

fi eld to more than 50 on the west side of the coal fi eld. Thus, 

correlating coal beds becomes more diffi cult from east to west 

simply because of the increased number of beds. Adding to 

this complexity, the depositional nature of the study interval 

is such that individual coal beds have varying thickness and 

limited lateral extent, which often makes correlating a single 

bed diffi cult if not impossible. However, grouping coal beds 

by zones eliminates these diffi culties. Four coal zones are 

recognized in the coal fi eld, and these zones are discussed 

in the text and displayed on the cross sections, and resource 

values are reported according to these subdivisions.

Cartographic Data

Geographic boundaries were imported as ARC/INFO 

coverages from existing public domain databases. Surface 

topography was obtained from a 1:250,000-scale digital elevation model (DEM) constructed by the USGS. County lines 

were obtained from 1:100,000-scale topologically interrogated 

geographic encoding and referencing (TIGER) fi les produced 

P6 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
T. 7 N.

R 88 W. R 87 W. 

R 91 W. R 89 W.

R 93 W. R 92 W.

R 90 W.

107 30' 

Hole drilled by the U. S. Geological SurveyOil and gas wellData point used only for elevation of the Trout Creek  Sandstone Member of the Iles Formation

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Figure 3. Location of Yampa coal fi eld public data points used for the coal assessment. Data points are identifi ed by map number in Appendix 2.
by the U.S. Bureau of the Census in 1990. Areas of surface 

and mineral ownership were obtained from 1:24,000-scale 

digital compilations provided by the Craig District Offi ce of 

the BLM. Maps showing areas of active and inactive coal 

leases were also obtained from the Craig District Offi ce BLM, 

confi rmed by the Colorado State Offi ce of the BLM, and 

digitized. Digital maps generated from ARC/INFO coverages 

of geologic features include stratigraphic boundaries, faults, 

fold axes, and strike and dip measurements. These geologic 

data were digitized by Green (1992) from the 1:500,000-scale 

geologic map of Colorado compiled by Tweto (1979). That 

part of the geologic map of Colorado covering the Yampa 

coal fi eld was compiled from the 1:250,000-scale geologic 

map of the Craig 1°×2° quadrangle, also compiled by Tweto 

(1976), which is based on 1:62,500-scale geologic maps by 

Hancock (1925) and Bass and others (1955). Figure 4 shows 

the 7.5′ quadrangle map coverage for the coal fi eld. Appendix 

7 contains the ArcView project that was used for the coal 

resource assessment, and Appendix 8 contains the stratigraphic 

database that was used in the assessment.

Acknowledgments

We would like to thank Janet Hook, Robert Ernst, and 

Jerry Strahan of the Craig District Offi ce of the BLM for 

supplying geophysical logs of coal exploration drill holes 

and maps showing active and inactive coal leases, and Matt 

McColm of the Colorado State Offi ce of the BLM for confi rming the lease maps. In addition, several mining companies 

granted permission for us to use selected priority data in our 

assessment, and we here extend our appreciation for this consideration. We also would like to thank USGS employees Ron 

Affolter for contributing coal-quality data, Laura Biewick for 

providing GIS support, Dorsey Blake for computer programming support, and Gary Stricker for computer programming 

support. USGS contract employees Tim Gognat, Jon Haacke, 

Al Heinrich, Tracey Mercier, and Marin Popov are acknowledged for their technical support. And last, we would like to 

thank USGS employees Mark Kirschbaum and Bob Hettinger 

for their peer reviews of the manuscript, and Rick Scott for 

his editorial work.

Geologic Setting

Cretaceous Paleogeography

During the Cretaceous Period, a large, north-trending 

epicontinental seaway, the Western Interior Seaway, occupied 

what is now central North America (fi g. 5). The seaway 

stretched from Mexico to Alaska, and, in what is now the 

central part of the United States, the width of the seaway 

extended from western Colorado to eastern Nebraska. A stable 

cratonic platform bordered the seaway on the east, and the 

tectonically active Sevier orogenic belt bordered the seaway 

on the west. Sediments moving eastward from the highlands 

were deposited along the fl uctuating shoreline, resulting in a 

complex package of Cretaceous sedimentary formations.

General Stratigraphy of Cretaceous 

Sedimentary Rocks in Northwestern Colorado

In ascending order, the Cretaceous lithostratigraphic units 

in northwestern Colorado are as follows: Lower Cretaceous 

Cedar Mountain Formation and Dakota Sandstone, Upper Cretaceous Mancos Shale, Mesaverde Group (Iles Formation and 

Williams Fork Formation), Lewis Shale, Fox Hills Sandstone, 

and Lance Formation. The Dakota Sandstone overlies the 

Upper Jurassic Morrison Formation, and a major unconformity 

separates the Lance Formation from the overlying Paleocene 

Fort Union Formation. The oldest Cretaceous unit exposed in 

the vicinity of the Yampa coal fi eld is the Dakota, which crops 

out on the west side of Steamboat Springs about 6 mi east of 

the coal fi eld, and near Juniper Hot Springs about 3 mi west 

of the coal fi eld. The youngest Cretaceous unit exposed the 

vicinity of the coal fi eld is the Lance Formation, which forms 

low hills just north of the coal fi eld.

Mesaverde Group in the Yampa Coal Field

Holmes (1877) applied the named Mesaverde Group to 

a thick interval of sandstone, mudrock (siltstone, mudstone, 

shale, and claystone), and coal in southwestern Colorado. 

Fenneman and Gale (1906b) noted a similar interval of rocks 

in the Yampa coal fi eld and extended the name Mesaverde 

into northwestern Colorado. Based on lithologic comparison, 

their correlation was correct. However, it is now known that 

the Mesaverde in northwestern Colorado is slightly younger 

than the Mesaverde in southwestern Colorado (Cobban and 

Reeside, 1952). Fenneman and Gale lowered the Mesaverde 

to formation status and included in it two regional sandstones, 

which they named the Trout Creek Sandstone and the Twentymile Sandstone Members. In addition, they noted that coal 

in the Mesaverde could be described as occurring in either 

a lower, a middle, or an upper coal group. The lower group 

contains all the coal below the Trout Creek, the middle group 

contains all the coal between the Trout Creek and the Twentymile, and the upper group contains all of the coal above the 

Twentymile.

Hancock (1925), working in the western part of the coal 

fi eld, raised the Mesaverde back to group status and subdivided it into the Iles Formation and overlying Williams Fork 

Formation, and defi ned the Trout Creek as a member at the top 

of the Iles and the Twentymile as a member more or less in 

the middle of the Williams Fork. Bass and others (1955) later 

extended these names into the eastern part of the coal fi eld. 

Masters (1966) introduced the name Mount Harris member 

for the lower part of those rocks between the Trout Creek 

P8 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
0 

Monument Butte Hamilton Pagoda Hayden Gulch Dunckley

Rattl

Juniper Hot Springs

Horse Gulch Round Bottom Castor Gulch Breeze Mountain Hayden Mount Harris

Lay

Lay SE Pine Ridge Craig Ralph White Lake Rock Spring Gulch Hooker Mountain Wolf 

Figure 4. Index map of 7.5′ quadrangles, Yampa coal fi eld.
Alluvial plain

and highlands

Coastal

plain

Peat

swamps

Western Interior

Seaway Thrust fault

30 Paleolatitude o

Sevier Highlands

Western

Interior

Seaway

Yampa 

coal field

45 o

30 o

30 o

45 o

Figure 5. Paleogeographic map of the central part of North America during the late Campanian (79–72 Ma) of the Late Cretaceous. The 

Yampa coal fi eld is shown in relation to the western shoreline, coastal plain, and peat swamps associated with the Western Interior Seaway.

Modifi ed from Roberts and Kirschbaum (1995).

P10 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
and the Twentymile, and reintroduced an earlier name, Holderness member, for those rocks in the Williams Fork above the 

Twentymile; neither of these names are used today.

In northwest Colorado, the Mesaverde (fi g. 6) comprises 

an eastward-thinning, wedge-shaped package of marine and 

nonmarine rocks that overlies and intertongues with the 

Mancos Shale, which contains Baculities perplexus in its 

upper part, and underlies and intertongues with the Lewis 

Shale, which contains Baculities clinolobatus (Izett and others, 

1971). Toward the east, the Mesaverde presumably pinches out 

into marine rocks of the Upper Cretaceous Pierre Shale, but 

evidence of this transition was lost to erosion when the Park 

Range was uplifted during the Tertiary. Toward the west, the 

Mesaverde becomes increasingly more nonmarine to the point 

that, in central Utah, equivalent strata are composed almost 

exclusively of conglomerate.

Detailed Stratigraphy of the Upper Cretaceous 

(Upper Campanian) Williams Fork Formation 

in the Yampa Coal Field

The Williams Fork Formation was named by Hancock 

(1925) for coal-bearing strata in the upper part of the 

Mesaverde Group in the western part of the Yampa coal fi eld 

(fi g. 7). These rocks are well exposed along the Williams Fork 

River and in the Williams Fork Mountains.

Mudrock is the most common lithology in the Williams 

Fork, followed by sandstone and lesser amounts of carbonaceous shale and coal. The mudrock occurs in various shades 

of brownish gray, is fi nely laminated, and usually contains 

varying amounts of carbonaceous debris. Fossil root traces are 

common. The sandstone is calcareous and appears light gray 

on fresh surfaces but typically weathers yellowish gray. The 

rock is composed of moderately well sorted, surrounded to 

subangular grains of quartz, chert, feldspar, and dark rock fragments that give fresh surfaces a salt-and-pepper appearance. 

Sandstone bodies include: (1) relatively thin, ripple-laminated 

sandstones that can be traced laterally, (2) relatively thick, 

trough cross-stratifi ed sandstones that are lenticular, and (3) 

relatively massive, cliff-forming sandstones of regional extent. 

In comparison to the other two types of sandstone bodies, 

regional sandstones are better sorted and contain a higher 

percentage of quartz grains, and the grains are more rounded. 

The carbonaceous shale is black on fresh surfaces and medium 

to dark brown on weathered surfaces. This lithology commonly grades laterally into coal. Coal occurs in thin to thick, 

lenticular beds that commonly pinch out or split laterally along 

strike. In some areas, the coal has burned, and the rocks 

directly adjacent to the burned bed are baked to a distinctive 

brick-red color.

Except for the thicker sandstone bodies, rocks in the Williams Fork Formation are poorly exposed throughout the coal 

fi eld. The formation rests conformably on the top of the Trout 

Creek Sandstone Member of the Iles Formation. Because the 

Trout Creek is usually well exposed, identifying the lower contact of the Williams Fork is relatively easy. The upper contact 

of the Williams Fork with the overlying Lewis Shale is also 

conformable, but identifying this contact can be more diffi cult. 

In the western part of the coal fi eld, the uppermost part of 

the Williams Fork is characterized by three, vertically stacked, 

thick sandstone bodies, and this juxtaposition of sandstone in 

the Williams Fork and shale in the Lewis makes identifying the 

contact possible. However, in the eastern part of the coal fi eld, 

these sand bodies are absent, and mudrock in the Williams 

Fork abuts shale in the Lewis. Here, identifying the contact can 

be very diffi cult.

In the western part of the coal fi eld, Hancock (1925) 

reported that the Williams Fork is approximately 1,600 ft 

thick, and Johnson (1987) reported the formation to be approxiimately 1,880 ft thick in the Round Bottom quadrangle southwest of Craig. In the eastern part of the coal fi eld, Bass and 

others (1955) reported the formation to range from 1,600 ft 

thick near Mount Harris to nearly 2,000 ft thick at the western 

margin of their study area. Only four drill holes used in the 

assessment penetrate the entire Williams Fork, and all four 

are located in the western part of the coal fi eld. From the 

geophysical logs of these holes, the thickness of the formation 

averages 1,915 ft.

North of the coal fi eld, a regional cross section by Roehler and Hansen (1989), which extends from the vicinity of 

Mount Harris, Colo., north-northwest to Cow Creek in the 

eastern Washakie Basin in southern Wyoming, shows that the 

Williams Fork is roughly equivalent to the uppermost part of 

the Allen Ridge Formation, the Pine Ridge Sandstone, and 

the Almond Formation. Northwest of the coal fi eld, a regional 

cross section by Roehler (1987), which extends from the vicinity of Mount Harris, Colo., northwest to Rock Springs, Wyo., 

shows that the Williams Fork is roughly equivalent to the 

upper part of the Ericson Sandstone and the Almond Formation. West of the coal fi eld, the term Williams Fork Formation 

is used to the vicinity of Pinyon Ridge, about 27 mi northwest 

of Meeker, Colo. (Hail, 1974). South of the coal fi eld, the term 

Williams Fork is used to the vicinity of Coal Basin, just east 

of Redstone, Colo., about 66 mi southeast of Meeker (Collins, 

1976).

In the pages that follow, thickness ranges are cited for 

sandstone units and for other stratigraphic intervals, and the 

reader will note considerable variability in these values. Some 

of this variability is natural, resulting from lateral changes 

in depositional facies. But three other factors can cause variability. First, measuring stratigraphic sections in the fi eld is 

diffi cult because the rocks are almost always poorly exposed. 

Even determining the thickness of regional sandstone units 

is problematic because the lower contact is usually gradational. Second, because of the poor exposure, the presence 

of normal faults can go undetected, and these faults have a 

tendency to thicken stratigraphic section. Third, the Williams 

Fork is composed of a variety of lithologies, and these units 

can change thickness over short distances. Because each lithology compacts differently, the thickness of a given stratigraphic 

interval can vary considerably.

Geology and Resource Assessment of the Middle and Upper Coal Groups, Yampa Coal Field, Northwestern Colorado P11
Three White sandstones

Big White sandstone

Twentymile Sandstone Membe

of Williams Fork Formation

Sub-Twentymile sandstone

Trout Cr

Mem

F

Tow Creek Sandstone Member of

Iles Formation

MANCOS SHALE

MESAVERDE GROUP

LEWIS SHALE

NW 

NET SHOREL

NET SHORELIN

Nonmarine deposits Nearshore marine deposits Marine deposits

Figure 6. Generalized northwest-southeast cross section of the Mesaverde Group in the Yampa coal fi eld showing the stratigraphic positions of major sands

from Seipman (1985).
Big White sandstone

Three White sandstones

Twentymile Sandstone Member

Sub-Twentymile sandstone

Yampa bed

Trout Creek Sandstone Member

0

400'

600'

800'

1000'

1200'

1400'

1600'

1800'

BIC

CZ

BIB

BZ

BIA

DZ

BIC

CZ

BIB

BZ

BIA

AZ

D coal zone

Barren interval C

C coal zone

Barren interval B

B coal zone

Barren interval A

A coal zone

AZ

AZ

DZ

DZ

200'

Iles Formation

Williams

Fork

Formation

middle

coal

group

upper

coal

group

Figure 7. Stratigraphic column for the Williams Fork Formation in the Yampa coal fi eld showing the stratigraphic positions 

of major sandstone units, coal zones, and barren intervals. 

Geology and Resource Assessment of the Middle and Upper Coal Groups, Yampa Coal Field, Northwestern Colorado P13
Trout Creek Sandstone Member (Iles Formation)

The Trout Creek Sandstone Member of the Iles Formation 

was named by Fenneman and Gale (1906b) for exposures 

along Trout Creek in the eastern part of the Yampa coal fi eld. 

Although the Trout Creek lies just below the Williams Fork 

Formation, it is discussed in this report because it is a signifi -

cant lithostratigraphic unit in the region. The Trout Creek is an 

impressive, cliff-forming unit of regional extent. Sandstone in 

the Trout Creek is very fi ne to medium grained and moderately 

well sorted, and the rocks become coarser grained and better 

sorted upward in the unit. The rock is almost white on fresh 

surfaces but weathers light yellowish gray. Bedding thickness 

ranges from thin to thick, with thickness increasing upward 

in the unit. Although the unit is best described as massive, 

especially in its upper part, hummocky and large-scale trough 

cross-stratifi cation are commonly observed. Marine trace fossils and the large bivalve Inoceramus sp. are locally present. 

The Trout Creek transitionally overlies an interval of marine 

shale containing Exiteloceras jenneyi (Izett and others, 1971) 

and is overlain by coal-bearing, nonmarine rocks. At many 

places a coal bed sits directly on the top of the Trout Creek. 

Fenneman and Gale (1906b) and Bass and others (1955) 

reported the Trout Creek to be about 100 ft thick in the eastern 

part of the coal fi eld, and Johnson (1987) reported that, in the 

subsurface of the Round Bottom 7.5′ quadrangle in the western 

part of the coal fi eld, the unit ranges from 67 to 79 ft thick. 

Siepman (1985), in his regional study of the unit, found that 

it ranges from 140 ft thick near Mount Harris to 31 ft thick 

at Middle Creek in the eastern part of the coal fi eld. Based on 

information compiled during the assessment, the thickness of 

the unit ranges from 28 to 145 ft, with an average thickness 

of about 67 ft. Toward the northwest, the Trout Creek pinches 

out in the subsurface of the Sand Wash Basin (Siepman, 1985; 

Roehler, 1987). Toward the southwest, the Trout Creek is well 

exposed in the Danforth Hills (Hancock and Eby, 1930), and, 

25 mi to the west in the Pinyon Ridge area, the unit is present 

in the 7.5′ Rough Gulch quadrangle (Hail, 1974). The Trout 

Creek pinches out west of Pinyon Ridge, but its nonmarine 

equivalent might be present in the western half of the Rangely 

7.5′ quadrangle (Cullins, 1971). Toward the south, the Trout 

Creek is equivalent to the Rollins Sandstone Member of the 

Iles Formation in the southern Piceance Basin of west-central 

Colorado (Collins, 1976).

Yampa Bed

Brownfi eld and Johnson (1986) introduced the informal 

term “Yampa bed” for a regionally signifi cant tonstein (altered 

volcanic ash) in the lower part of the Williams Fork Formation 

in the middle part of the A coal zone (fi g. 7; pl. 1, fi gs. C and 

D). Where rarely exposed on the surface or observed in drill 

core, the unit is seen to be a grayish-white, structureless claystone that weathers blocky. Typically, the unit is sandwiched 

between two coal beds, and both the lower and upper contacts 

are sharp. In the subsurface, the unit becomes an important 

regional marker bed that is easily identifi ed on the geophysical 

logs of coal and oil and gas exploration drill holes. In the case 

of coal exploration logs, the unit displays low natural gamma 

and very low single-point resistance. Based on information 

compiled during the assessment, the thickness of the Yampa 

bed ranges from less than 1 ft to 6 ft thick, but the unit can 

be absent locally. The average thickness of the unit is about 

3 ft. In the western and central parts of the Yampa coal fi eld, 

the unit lies between 113 and 259 ft above the top of the 

Trout Creek Sandstone Member, with an average value of 178 

ft. However, in the eastern part of the coal fi eld, the Trout 

Creek rises stratigraphically, and, in this area, the stratigraphic 

separation is less than 20 ft—on some geophysical logs, the 

Yampa bed appears to rest directly on the Trout Creek (pl. 1, 

fi g. C). The Yampa bed has also been identifi ed in the Danforth 

Hills and in the subsurface of the Sand Wash Basin.

Sub-Twentymile Sandstone

The informal term “sub-Twentymile sandstone” was 

introduced by Kiteley (1983) for a sandstone unit that lies 

about 150 ft below the base of the Twentymile Sandstone 

Member of the Williams Fork Formation in the east-central 

part of the Yampa coal fi eld (fi g. 7; pl. 1, fi g. C). Most of 

what is known about this unit comes from the subsurface, 

but it probably has many physical characteristics in common 

with the Trout Creek and Twentymile Sandstone Members. 

Based on information compiled during the assessment, the 

unit averages about 30 ft in thickness, contains one to three 

sandstone bodies, and is overlain by the B coal zone. Masters 

(1966) defi ned an informal sandstone unit, the Hayden Gulch 

sandstone, at this same stratigraphic level, and this sandstone 

is undoubtedly equivalent to the sub-Twentymile. Siepman 

(1985) recognized the sub-Twentymile and included it at the 

top of his sub-Twentymile unit. The sub-Twentymile sandstone 

pinches out toward the east, and it loses its distinctiveness 

toward the west by splitting into a number of smaller sandstone bodies, but the overlying B coal zone continues through 

the western part of the coal fi eld.

Twentymile Sandstone Member of the 

Williams Fork Formation

The Twentymile Sandstone Member of the Williams Fork 

Formation was named by Fenneman and Gale (1906b) for 

exposures in Twentymile Park in the eastern part of the Yampa 

coal fi eld. Based on information compiled during the assessment, the stratigraphic distance between the top of the Trout 

Creek Sandstone and the base of the Twentymile ranges from 

575 to 1,091 ft, with an average of about 839 ft. Thickness 

values greater than 1,000 ft occur on the eastern side of the 

coal fi eld, presumably because of a thickening of the marine 

shale under the Twentymile. The Twentymile typically forms 

P14 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
distinctive cliffs of yellowish-gray-weathering sandstone. Lithologically, the Twentymile is very similar to the Trout Creek. 

Grain size ranges from very fi ne to medium, and the fragments 

are moderately well sorted. The rocks are light gray on fresh 

surfaces and become coarser grained and better sorted in 

the upward direction. Bed thickness also increases upward. 

Hummocky and large-scale trough cross-stratifi cation are commonly observed, as are marine trace fossils. Unlike the Trout 

Creek, the Twentymile often consists of two to three individual 

sandstone bodies separated by fi ner grained material. The 

Twentymile transitionally overlies a thick interval of marine 

shale containing Baculities reesidei (Izett and others, 1971) 

and is overlain by coal-bearing, nonmarine rocks. At many 

places a coal bed sits directly on the top of the Twentymile. 

Bass and others (1955) reported that the Twentymile is about 

100 to 200 ft thick in the eastern part of the coal fi eld. Siepman 

(1985) reported that the unit ranges from 184 ft thick in Fish 

Creek Canyon in the eastern part of the coal fi eld to 28 ft thick 

at Duffy Mountain in the western part of the coal fi eld. Based 

on information compiled during the assessment, the thickness 

of the Twentymile ranges from 12 to 133 ft, with an average 

thickness of about 63 ft. Although the thickness varies, in 

general, values less than 30 ft tend to occur in the western part 

of the coal fi eld, and values greater than 100 ft tend to occur 

in the eastern part of the coal fi eld. The Twentymile is less 

laterally extensive than the Trout Creek. It begins to loose its 

identity on the western edge of the coal fi eld and is known to 

pinch out toward the northwest in the subsurface of the Sand 

Wash Basin (Siepman, 1985). Moreover, the Twentymile is not 

present to the southwest in the Danforth Hills.

Big White Sandstone

The informal term “Big White sandstone” was introduced 

by W.R. Grace and Company for a poorly exposed sandstone 

that lies above the Twentymile Sandstone Member in the central part of the Yampa coal fi eld. In the western part of the 

coal fi eld, a somewhat discontinuous sandstone is present at 

the same stratigraphic level as the Big White, and in the 

Round Bottom 7.5′ quadrangle Johnson (1987) referred to 

it as the unnamed upper sandstone member of the Williams 

Fork Formation. Several geologists with the USGS who have 

worked in the area refer to this informal unit as the Fuhr 

Gulch sandstone. In the eastern part of the coal fi eld, another 

sandstone is present at the same stratigraphic level as the 

Big White, and this informal unit was indirectly defi ned as 

the Fish Creek sandstone by Campbell (1923) in his description of the overlying Fish Creek coal bed. With little doubt, 

all three sandstones are equivalent and represent a poorly 

exposed, regional unit (fi g. 7; pl. 1, fi gs. B and E). Little is 

known about the physical characteristics of the Big White. 

However, Johnson (1987), in his discussion of the unnamed 

upper sandstone member of the Williams Fork in the Round 

Bottom 7.5′ quadrangle, describes the unit at the mouth of 

Fuhr Gulch as a light-gray-weathering, very fi ne to fi negrained sandstone. Here, the unit is 39 ft thick and lies about 

200 ft above the Twentymile. Based on information compiled 

during the assessment, the stratigraphic distance between the 

top of the Twentymile and the base of the Big White (or its 

lateral equivalents) ranges from 90 to 248 ft, with an average 

value of about 179 ft. The thickness of the unit ranges from 5 

to 54 ft, with an average value of about 31 ft.

Three White Sandstones

In the western part of the Yampa coal fi eld, the upper 

part of the Williams Fork Formation contains three, thick, 

conspicuous sandstone bodies that are informally referred to 

by several geologists with the USGS who have worked in the 

area as the “Three White sandstones” (fi g. 7; pl. 1, fi g. B). 

Lithologically, the three sandstones resemble the Twentymile 

Sandstone Member in almost every detail. In addition, each 

sandstone overlies a thin interval of fi ner grained rocks of 

possible marine affi nity and each sandstone is overlain by 

nonmarine rocks that are usually coal bearing. In some places, 

a coal bed lies directing on the sandstone. Each of the three 

sandstones is 50 to 60 ft thick, but exceptions are common. 

Where best exposed along the Yampa River southwest of Craig 

(T. 6 N., R. 91 W., secs. 19 and 30), the base of the lower 

sandstone lies about 310 ft above the top of the Big White 

sandstone—the stratigraphic distance between the base of the 

lower sandstone and the top of the upper sandstone is about 

320 ft—and the base of the Lewis Shale lies about 115 ft above 

the top of the upper sandstone. Toward the west, the lower 

and middle sandstones pinch out, but the upper sandstone 

continues to the edge of the coal fi eld. Toward the east, the 

three sandstones continue for several miles east of the Yampa 

River, but, farther east, the sandstones are diffi cult to identify 

on the surface. In the subsurface, evidence of their existence 

is lacking because all of the coal exploration drill holes were 

spudded stratigraphically below the expected level of the lower 

sandstone. It should be mentioned that, where the Three White 

sandstones are well exposed along the Yampa River, another 

thick sandstone body exists at the very top of the Williams 

Fork in sharp contact with the Lewis. This so-called sub-Lewis 

sandstone is less distinct than those below, and it lacks many 

of the characteristics shared by the other three. Moreover, it 

is diffi cult to trace laterally both on the surface and in the 

subsurface. On the western edge of the coal fi eld, a single 

coal bed appears in the subsurface high above the stratigraphic 

level of the highest coal associated with the upper sandstone, 

and this coal bed might lie above the sub-Lewis sandstone. If 

this is true, then the sub-Lewis sandstone is probably a poorly 

developed fourth sandstone in the series.

Geology and Resource Assessment of the Middle and Upper Coal Groups, Yampa Coal Field, Northwestern Colorado P15
Depositional Environments Represented 

in the Williams Fork Formation

During the Late Cretaceous, the western edge of the 

Western Interior Seaway was continually modifi ed by sediment infl ux from tectonically active areas to the west. According to Haun and Weimer (1960), as much as 11,000 vertical 

feet of sediment were deposited in the seaway during this 

time. In what is now northwestern Colorado, this western 

tectonism is referred to as the Sevier orogenic belt, and periods of increased tectonic activity can be related to periods 

of increased sediment progradation. Because of the interplay 

between sediment progradation (regression) and marine fl ooding (transgression), the position of the shoreline fl uctuated 

back and forth with time. Depositional dip was toward the 

southeast and depositional strike rotated from northeast trending to northwest trending during deposition of the Williams 

Fork Formation (Zapp and Cobban, 1960). 

The sediments deposited in northwestern Colorado during 

this time are now contained in the Iles and Williams Fork Formations of the Mesaverde Group (fi g. 6). Masters (1966) recognized three large-scale, regressive cycles in the Mesaverde: 

(1) from the base of the Iles to the base of the marine shale 

underlying the Trout Creek Sandstone Member, (2) from the 

base of the Trout Creek to the base of the marine shale underlying the Twentymile Sandstone Member, and (3) from the 

base of the Twentymile Sandstone to the top of the Williams 

Fork. In each cycle, the top of the coal-bearing package and 

the base of the overlying marine shale are separated by a 

transgressive disconformity. In general, the Iles represents a 

net shoreline regression and the Williams Fork represents a net 

shoreline transgression. However, in detail, the Williams Fork 

shows evidence of several shoreline fl uctuations, as evidenced 

by the vertical juxtaposition of the formation’s three major 

depositional settings: offshore marine, nearshore marine, and 

fl uvial.

Offshore Marine Mudrock

The westward-thinning tongues of mudrock that directly 

underlie the Trout Creek and Twentymile Sandstones Members 

were deposited on an open-marine shelf, as evidenced by the 

presence of marine body fossils and deep-marine trace fossils. 

Most likely, this same environment is represented in the strata 

that directly underlie the sub-Twentymile sandstone in the 

eastern part of the coal fi eld, and a somewhat shallower marine 

environment is probably represented in the strata that directly 

underlie the Three White sandstones in the western part of the 

coal fi eld. The characteristics of the strata that directly underlie 

the Big White sandstone are poorly known, but it is quite 

possible that these rocks are also marine.

Nearshore Marine Sandstone

The sandstones contained in the Trout Creek Sandstone 

Member, sub-Twentymile sandstone, Twentymile Sandstone 

Member, Big White sandstone, and in the Three White sandstones were deposited in a nearshore marine environment. This 

conclusion is supported by an upward increase in grain size 

and an upward increase in bed thickness, hummocky crossstratifi cation followed upward by trough cross-stratifi cation, 

and the occurrence of shallow-marine trace fossils, especially 

Ophiomorpha. Relatively complete stratigraphic sections of 

the Trout Creek and Twentymile reveal that the units are composed of a basal transitional part, deposited below wave base, 

and an overlying shoreface part, deposited above wave base 

but below low tide level. Some exposures also contain a higher 

foreshore part, deposited between low- and high-tide levels—

some rare exposures are capped by a backshore part, deposited 

above high-tide level. Many workers, most recently Seipman 

(1985), believe that the Trout Creek and Twentymile were 

deposited along a wave-dominated, deltaic strand plain and 

barrier-island system in a microtidal setting.

Nonmarine Deposits

The strata that directly overly the nearshore marine sandstones probably accumulated in lagoonal settings, whereas 

all of the higher strata most likely accumulated as fl uvial 

deposits on a coastal plain that sloped gently seaward with 

little topographic relief. Two main fl uvial environments are 

represented in the coastal-plain system: channel and overbank. 

Lenticular, fi ning-upward sandstone bodies represent the active 

channel fi ll of high-sinuosity streams, and the much more 

subtle lenticular bodies of mudrock represent abandoned-channel fi ll. Interbedded strata deposited in the overbank environment include: (1) intervals of very fi ne grained sandstone and 

mudrock representing levee deposits, (2) intervals of mudrock 

containing abundant fossil root traces representing fl ood-plain 

deposits, and (3) tabular bodies of ripple-laminated, fi ne- to 

very fi ne grained sandstone representing splay deposits. Coal 

beds positioned on or just above the nearshore marine sandstones perhaps represent peat that accumulated in lagoons that 

separated barrier islands from the mainland. Coal beds positioned higher in the stratigraphic section probably represent 

peat that accumulated in swamps that existed in interchannel 

areas on the coastal plain. The nonmarine successions that 

overlie the Trout Creek Sandstone Member, sub-Twentymile 

sandstone, Twentymile Sandstone Member, and the Big White 

sandstone each consist of a lower coal-bearing part (coal zone) 

and an overlying part that does not contain coal (barren interval). Most likely, the coal-bearing part represents an environment low on the coastal plain where the gradient was at its 

lowest and the water table was at its highest. The overlying 

P16 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
part that does not contain coal is marine in its upper portion, 

especially in the eastern part of the Yampa coal fi eld, but the 

nonmarine lower portion perhaps represents an environment 

higher on the coastal plain where conditions did not favor the 

formation of swamps.

Brief History of the Deposition of the 

Mesaverde Group in the Yampa Coal Field

Prior to the deposition of the Mesaverde Group (fi g. 6), 

the western shoreline of the Western Interior Seaway was 

positioned about 75 mi west of what is now the Yampa coal 

fi eld (Zapp and Cobban, 1960), and, in the area of the coal 

fi eld, marine mud—now contained in the Mancos Shale—was 

accumulating. The lowest unit of the Mesaverde, the Tow 

Creek Sandstone Member of the Iles Formation (Crawford and 

others, 1920), was deposited when a major eastward migration 

of the sea moved the shoreline to the area of the coal fi eld, 

and nearshore marine sand was deposited over marine mud. 

As the shoreline continued to move eastward beyond the coal 

fi eld, nonmarine rocks now contained in the main body of the 

Iles were deposited over the Tow Creek, and this part of the 

Iles contains some coal. The depositional history of the main 

body of the Iles is not well documented, but several minor 

oscillations of the shoreline occurred during this time, and 

rocks representing these events are now contained in this part 

of the formation (Kiteley, 1980). Toward the end of Iles time, 

the shoreline moved westward back across the coal fi eld, 

fl ooding the area with seawater, and marine mud was deposited 

over the nonmarine sediments. This event is now recorded 

in the marine shale that directly underlies the Trout Creek 

Sandstone Member of the Iles. At the very end of Iles time, 

the shoreline again moved eastward to the area of the coal 

fi eld and the nearshore marine sand of the Trout Creek was 

deposited (Siepman, 1985).

The fi rst phase of Williams Fork deposition occurred as 

the shoreline continued to move eastward beyond the coal 

fi eld: nonmarine sediments accumulated just behind the beach 

or low on the coastal plain, and this interval now contains 

coal (A coal zone). Following this, sediments were probably 

deposited higher on the coastal plain, and this higher interval 

lacks coal (lower part of barren interval A). On the eastern 

side of the coal fi eld, a minor westward shift of the shoreline 

caused an interval of marine mud to be deposited, followed by 

a minor eastward shift of the shoreline that allowed nearshore 

marine sand to be deposited—these two events are now represented by rocks contained in the sub-Twentymile sandstone 

and its underlying marine shale (upper part of barren interval 

A). As the shoreline continued to move eastward, nonmarine 

sediments accumulated above the sub-Twentymile, and this 

interval now contains coal (B coal zone). The nonmarine rocks 

directly above this interval lack coal (lower part of barren 

interval B). Finally, the shoreline again moved westward back 

across the coal fi eld, fl ooding the area with seawater, and 

marine mud was deposited over the nonmarine sediments. 

This mud is now represented by the marine shale (upper part 

of barren interval B) that lies directly under the Twentymile 

Sandstone Member of the Williams Fork.

The last phase of Williams Fork deposition occurred 

when the shoreline again moved eastward across the area of 

the coal fi eld, and the nearshore marine sand and overlying 

nonmarine rocks now contained in the Twentymile and upper 

part of the Williams Fork were deposited. As occurred earlier, 

the fi rst nonmarine sediments were deposited just behind the 

beach or low on the coastal plain, and this interval now contains coal (C coal zone). In the interval above, coal is not 

present because the sediments were probably deposited higher 

on the coastal plain (barren interval C). At this point, the depositional history of the Williams Fork becomes obscure. What 

is known is that (1) a signifi cant sandstone, the Big White 

sandstone, was deposited more or less across the entire coal 

fi eld, and (2) the interval overlying the sandstone contains coal 

(D coal zone). Most likely, the Big White represents another 

couplet of shoreline shifts and subtle marine characteristics 

that will eventually be described in the unit, and the rocks 

directly below the sandstone will prove to have a marine affi nity. The depositional history at the close of Williams Fork 

time is more clear. A major westward migration of the sea 

caused the area to be covered by seawater, and marine mud 

was deposited, which is now contained in the Lewis Shale. 

This signaled the end of Mesaverde deposition in northwestern 

Colorado. However, the event was interrupted at least three 

times by minor oscillations of the shoreline, during which time 

the Three White sandstones and their associated rocks were 

deposited.

Post-Mancos Shale Regional Cretaceous 

Stratigraphy in Northwestern Colorado

The Cretaceous formations above the Mesaverde Group 

in the area of the western Williams Fork Mountains (the Lewis 

Shale, Fox Hills Sandstone, and Lance Formation) have not 

been recognized to the southwest in the Danforth Hills (fi g. 

8). Moreover, the thickness of strata assigned to the Williams 

Fork Formation increases from 1,900 ft in the Williams Fork 

Mountains to 4,775 ft in the Danforth Hills. The depositional 

conditions that lead to this conundrum have been pondered by 

geologists for many years. West of the Danforth Hills, in the 

vicinity of Rangely, Colo., the post-Mancos Shale stratigraphic 

section is much thinner, suggesting that Tertiary erosion has 

removed a signifi cant amount of Cretaceous rock. Because 

much of the post-Mancos depositional history has been lost to 

erosion in this area, solving the riddle must rely on evidence 

obtained from the Williams Fork Mountains and Danforth 

Hills.

Part of the solution involves the Axial Basin anticline, 

the structural feature that separates the southeastern part of 

the Sand Wash Basin, including the Williams Fork Mountains, 

Geology and Resource Assessment of the Middle and Upper Coal Groups, Yampa Coal Field, Northwestern Colorado P17
Upper unit

North

Rangely

South

Pinyon

Ridge

Central

Danforth Hills

Coal unitLower unitSego Ss

Upper coal zone

Lion Canyon SsLion Canyoncoal groupGoff coal groupFairfield coal groupTrout Creek Ss MbrRim Rock ssBarren intervalUpper barrenzone

Middle coal zoneLower coal zoneTrout Creek Ss MbrBasal ss

0

1000'2000'3000'

0

1000'2000'3000'

0

1000'2000'3000'5000'4000'6000'

Mesaverde

Gp

Williams

Fork Fm

0

1000'2000'3000'4000'5000'6000'

Fox Hills Ss

??

1

2

3

Iles Fm

Williams

Fork Fm

Iles Fm

Lance Fm

Iles Fm

Williams

Fork Fm

Lewis Sh

1

Craig

Meeker Rangely

2

3

4

Location map of cross section in northwestern Colorado

Figure 8. Generalized regional cross section of the Mesaverde Group and younger Cretaceous formations in northwestern Colorado. No horizontal scale im
from the northeastern part of the Piceance Basin, including the 

Danforth Hills. This feature is probably related to an underlying weakness in the crust, and tectonic activity in this area 

could possibly date from the Precambrian (Stone, 1986). If 

the area of the present-day Axial Basin was active during the 

Late Cretaceous, it is fair to assume that the shape of the 

western coastline of the Western Interior Seaway was modifi ed 

in response to the tectonism and that the Late Cretaceous 

depositional history in this small area is somehow unique. 

Presumably, sometime during the late Tertiary, the area of the 

Axial Basin was uplifted above the surrounding terrain, and 

the post-Mancos rocks were subjected to differential erosion. 

As a result, the soft shales of the Mancos were exposed in 

the core of the fold, and continued erosion of these rocks has 

resulted in the topographic depression (or basin) seen today. 

Because the post-Mancos rocks have been lost to erosion, the 

complete depositional history of this area will never be known. 

Indeed, it will never be known if any post-Mancos rocks were 

even deposited.

The fi rst geologist to publish his thoughts on the subject 

was Gale (1910), who postulated that either the Lewis, Fox 

Hills, and Lance were never deposited in the area of the Danforth Hills, or they were deposited but subsequently removed 

by Tertiary erosion. Sears (1925), and later Masters (1959), 

thought that a regional facies change could explain both the 

absence of these units as well as the increased thickness of 

the Williams Fork Formation. Both workers suggested that the 

Lewis sea did not transgress into the area of the Danforth 

Hills, and therefore no marine shale was deposited. If this is 

true, then the thick shale unit (Lewis Shale) that separates and 

defi nes the top of the Williams Fork Formation from the base 

of the overlying Cretaceous units (Fox Hills and Lance) in the 

Williams Fork Mountains is simply not present in the Danforth 

Hills. Thus, rocks equivalent to the Fox Hills and Lance are 

actually present in the Danforth Hills but remain unidentifi ed 

in the upper part of the Williams Fork Formation. By this 

hypothesis, the Lion Canyon Sandstone Member of the Williams Fork Formation in the Danforth Hills, known to contain 

brackish-water bivalves, might represent deposition at, or near, 

the locality of maximum transgression of the Lewis sea. The 

Lion Canyon might therefore be a retrogradational and progradational stack of nearshore marine sandstones that includes 

equivalents of the Three White sandstones in the upper part 

of the Williams Fork Formation and the Fox Hills Sandstone, 

respectively, in the Williams Fork Mountains.

In conclusion, the coal in the upper part of the Williams 

Fork Formation in the Danforth Hills, the Lion Canyon coal 

group, is possibly equivalent to coal in the Lance in the Williams Fork Mountains, and the Mesaverde Group coal in the 

Rangely area is probably equivalent to the Fairfi eld coal group 

of the Williams Fork Formation in the Danforth Hills.

Post-Cretaceous Deformational History 

of Northwestern Colorado

Near the end of the Cretaceous, the Western Interior 

Seaway withdrew from what is now northwestern Colorado, 

and marine and coastal-plain deposition ceased. This event was 

followed closely by compressional tectonism associated with 

the onset of the Laramide orogeny. In northwestern Colorado, 

the Lance and older rocks were folded, mildly uplifted, and 

eroded, and the peneplain that resulted is now represented 

by a regional unconformity. As the orogeny intensifi ed in 

earliest Tertiary, the Park Range was uplifted and eroded and 

a thin veneer of gravel spread westward as an alluvial fan 

over the erosional surface. This deposit now forms the basal 

conglomerate of the Paleocene Fort Union Formation. With 

the uplift of the Park Range and other Laramide structures, 

the ancestral Sand Wash Basin was defi ned, and all Tertiary 

formations younger than the Fort Union are fi ner grained and 

show lateral facies changes consistent with deposition in a 

slowly subsiding basin. During the middle and late Tertiary, 

extensional tectonism resulted in numerous normal faults and 

volcanism in the region. The various volcanic features and 

deposits located northwest of Steamboat Springs are Miocene 

in age.

Structural Features of the Yampa Coal Field

The Yampa coal fi eld occupies the southeastern corner of 

the Sand Wash Basin (Tweto, 1976), and this is refl ected in 

the gross regional structure of the coal fi eld (fi g. 9). In the 

western and central parts of the coal fi eld, the structural dip is 

toward the north, but farther to the east, the regional structure 

swings counterclockwise until, in the northeastern part of the 

coal fi eld, north of Mount Harris, the dip is toward the west. 

Another regional structure of signifi cance in the area of the 

coal fi eld is the northwest-trending Axial Basin anticline. This 

structure borders the coal fi eld on the southwest and defi nes 

the boundary between the Sand Wash Basin on the north and 

the Piceance Basin on the south. According to Stone (1986), 

this fold is a minor part of a much larger tectonic structure that 

extends from the Uinta Mountains in northeastern Utah to the 

Eagle Basin in north-central Colorado. The anticlinal nature 

of the fold, as seen on Stone’s cross sections, results from 

the doming of strata above a southwest-vergent thrust fault. 

Although movement along this regional trend might date from 

the Precambrian, the current Axial Basin anticline probably 

formed during the Laramide orogeny at the same time that 

smaller, subparallel folds were forming toward the north in the 

coal fi eld.

Geology and Resource Assessment of the Middle and Upper Coal Groups, Yampa Coal Field, Northwestern Colorado P19
8000 8500

8000 7500

8000

7000

6500 8000 

6000 7500 

7000 

7500 6000 

650

7500 8000 

5500 

7000

6500

5500

6000

7000

7000

5000

6500

6500

4500

4000

3500

3000

2500

2000

1500

6000 

7000 5500 

7000 5000

7000

R 88 W. R 87 W. 

R 91 W. R 90 W. R 89 W.

R 93 W. R 92 W.

107 30' 

Fault, bar and ball on downthrown sideSurface outcrop of the Trout Creek Sandstone MemberStructure contour (contour interval 500 ft)

0 5 

3500

7000

Figure 9. Structure contour map drawn on top of the Trout Creek Sandstone Member of the Iles Formation, Yampa coal fi eld. Surface outcrop of the Trout Cr

1:250,000-scale geologic map of the Craig 1°×2° quadrangle compiled by Tweto (1976). Contours generated from surface elevations and subsurface elevations base used in the coal assessment. Only those faults known to offset the top of the Trout Creek are shown.
Folding in the coal fi eld occurred after deposition of 

the Lance Formation but before deposition of the Fort Union 

Formation (Tweto, 1976). In general, folds within the coal 

fi eld can be grouped into a western group and an eastern 

group (fi g. 10). On the east side of the coal fi eld, south and 

east of Hayden, the fold axes trend north-northwest and northnortheast and plunge in a southerly direction. These folds are 

asymmetrical, with their axial planes inclined in a westerly 

direction. Starting from the west, the more signifi cant folds 

are the Sage Creek anticline, the Fish Creek anticline, the 

Twentymile Park syncline, and the Tow Creek anticline. The 

Twentymile syncline is doubly plunging, and a structural basin 

containing Lewis Shale accounts for the broad open area, or 

park, south of Milner. On the western side of the coal fi eld, 

south and west of Craig, fold axes trend and plunge toward 

the northwest. Most of the folds are also asymmetrical, with 

their axial planes inclined toward the northeast. Starting from 

the west, the more signifi cant folds are the Round Bottom 

syncline, the Williams Fork anticline, the Big Bottom syncline, 

and the Breeze Mountain–Buck Peak anticline.

South of the western part of the coal fi eld, folds trend 

and plunge toward the northwest and are asymmetrical with 

their axial planes inclined toward the northeast, thus following 

the structural pattern in the western part of the coal fi eld. The 

dominant fold in this area is the Hart syncline. This structure 

is bounded on the north by the Beaver Creek anticline and 

on the south by the Seely anticline. The axes of these folds 

trend northwest, but the axis of the Hart syncline and the 

Seely anticline eventually veer westward. The Hart syncline 

is a doubly plunging structure, and the resistant Trout Creek 

Sandstone Member holds up the fold as a topographic high 

with a depressed basin in its center. 

Faulting in northwestern Colorado commenced sometime 

in the middle or late Tertiary, and, in the Sand Wash Basin, 

units as young as the Miocene Browns Park Formation have 

been displaced (Tweto, 1976). Undoubtedly, faulting continued 

into the Quaternary, and the region still experiences rare, mild 

earthquakes. Most of the faults in the coal fi eld are high-angle 

normal faults that trend northwest (fi g. 10). Displacements 

are down to the northeast or southwest, and horst-and-graben 

structures are common. Overall, faulting has not disrupted the 

gross structure of the coal fi eld to any signifi cant degree.

Coal Assessment

On the map “Coal Fields of the Conterminous United 

States” (Tully, 1996), the Yampa coal fi eld is shown to be 

in the southeastern corner of the Green River Region of the 

Rocky Mountain Province. Both Cretaceous- and Paleoceneage coal occur in this area, but only the coal in the Mesaverde 

Group is of economic signifi cance at this time. Of the three 

coal groups in the Mesaverde, as defi ned by Fenneman and 

Gale (1906b), only the middle and upper groups in the Williams Fork Formation were considered in this assessment. 

Several large mines are currently extracting coal from these 

two groups, and future coal leasing and subsequent mining 

will most likely be restricted to coal in these two groups. 

The lower coal group, which comprises the coal in the Iles 

Formation, was not considered in this assessment because the 

coal is currently subeconomic. Notable closed mines in the Iles 

include the Pinnacle mine, located about 1 mi southeast of Oak 

Creek; the Bear River mine, located about 1 mi northeast of 

Mount Harris; and the Sun and Rice mines, located in Hayden 

Gulch in the south-central part of the coal fi eld.

The Lance Formation contains a minor amount of coal, 

notably the 3- to 10-ft-thick Lorella bed, positioned about 50 

ft above the base of the formation, and the 10- to 14-ft-thick 

Kimberley bed, positioned about in the middle of the formation (Bass and others, 1955). There is also a signifi cant amount 

of coal in Fort Union Formation, notably the Seymour bed in 

the upper part of the formation—this bed can be as thick as 17 

ft. There is currently no interest in extracting coal from either 

of these formations, and therefore they were not included in 

this assessment.

During deposition of the Williams Fork, the area that 

is now northwestern Colorado was at a latitude of about 42 

degrees north (Roberts and Kirschbaum, 1995) and had a 

humid, subtropical climate. This favorable climate, coupled 

with a high water table characteristic of a lower-coastal-plain 

depositional setting, facilitated the development of a complex 

network of peat swamps that were interspersed with fi negrained siliciclastic sediments. Because of this complexity, 

coal in the Williams Fork is widely distributed, both vertically 

and horizontally, and coal beds commonly pinch out or split 

laterally over relatively short distances, making regional correlations of individual beds diffi cult. Correlation problems are 

made more diffi cult because each mine in the western and 

central parts of the coal fi eld has developed their own bed 

nomenclature. This is not the case on the eastern side of the 

coal fi eld, where there are only three major coal beds and their 

names are in common use by all of the mining companies.

Coal Distribution

Based on regional cross sections (pl. 1, fi gs. B, C, and D), 

coal in the Williams Fork Formation can be grouped into four 

zones, two in the middle coal group and two in the upper coal 

group (fi g. 7). These zones are defi ned in terms of the regional 

sandstone units in the formation and three barren intervals that 

can be traced throughout the coal fi eld. Local variations in 

thickness for coal zones and barren intervals can result from 

differing compaction ratios of the varying non-coal lithologies. 

In analyzing a particular coal zone or barren interval, only 

those drill holes that were commenced above the zone or 

interval and completed below the zone or interval where used. 

This criteria insured that only complete stratigraphic sections 

were used.

Geology and Resource Assessment of the Middle and Upper Coal Groups, Yampa Coal Field, Northwestern Colorado P21
 R. 94 W. R. 93 W. R. 92 W. R. 91 W. R. 90 W. R. 89 W. R. 88 W. 

 R. 87 W. 

1 3

4

2

10

11

5

6

7

8

9

● ●

● ●

●

●

●

●

●

●

●

● ●

●

● ● ●

●

●

●

●

●

Hayden

Craig

Lay

●

Mount Harris

107 30' 

Explanation

SynclineAnticlineWilliams Fork FormationIles Formation

1. Round Bottom syncline2. Williams Fork anticline3. Big Bottom syncline4. Breeze Mountain - Buck Peak anticline5. Sage Creek anticline6. Fish Creek anticline7. Twentymile Park syncline8. Tow Creek anticline9. Hart syncline

10. Beaver Creek anticline11. Seely anticline

Fault (ball on downthrown side) ●

0 5 mi

Figure 10. Generalized geology of the Yampa coal fi eld showing the Iles and Williams Fork Formations and major folds and faults. Modifi ed after the 1:250,00

the Craig 1°×2° quadrangle compiled by Tweto (1976).
A Coal Zone

The A coal zone is defi ned as the interval that extends 

from the top of the Trout Creek Sandstone Member to the top 

of the fi rst coal bed below barren interval A. In the eastern and 

central parts of the coal fi eld, the coal zone is quite distinct, 

but in the western part of the coal fi eld, barren interval A is 

much thinner (pl. 1, fi g. C)—in this area separating the A and 

B coal zones can be problematic. The Yampa bed is positioned 

more or less in the middle of the A coal zone in the western 

and central parts of the coal fi eld, but, along the eastern margin 

of the coal fi eld, the Yampa bed drops stratigraphically and in 

some places appears to set almost on top of the Trout Creek. 

Based on information compiled during the assessment, the 

thickness of the interval between the base of the lowest coal 

bed to the top of the highest coal bed ranges from 202 to 463 

ft, and averages about 350 ft. This interval excludes a variable 

thickness of rock that lies above the Trout Creek and below 

the lowest coal bed.

Based on drill-hole data collected during the assessment, 

the A coal zone contains the most coal beds and has the greatest net thickness of coal of the four coal zones in the Williams 

Fork Formation. The number of coal beds increases from east 

to west. On the eastern side of the coal fi eld, in the Rattlesnake 

Butte, Milner, and Oak Creek 7.5′ quadrangles (fi g. 4), the 

number of coal beds ranges from four to nine, with an average 

of fi ve. On the western side of the coal fi eld, in the Horse 

Gulch and Round Bottom 7.5′ quadrangles, the number of coal 

beds ranges from eight to 23, with an average of 14. The net 

thickness of coal also increases from east to west (fi g. 11). 

On the eastern side of the coal fi eld, in the Rattlesnake Butte, 

Milner, and Oak Creek 7.5′ quadrangles, the net thickness of 

coal ranges from 20 to 27 ft, with an average of 24 ft. On the 

western side of the coal fi eld, in the Horse Gulch and Round 

Bottom 7.5′ quadrangles, the net thickness of coal ranges from 

31 to 97 ft, with an average of 66 ft. In the Hart syncline 

(fi g. 10), south of the main area of the coal fi eld, the average 

number of beds, 13, is similar to the average for the western 

part of the coal fi eld. However, the net thickness of coal, 87 

ft, exceeds the average for the western part of the coal fi eld. 

Figure 11 also shows a trend of net coal greater than 80 ft that 

extends in a northwesterly direction from the western half of 

the Hart syncline. The thickest single coal bed in the A coal 

zone encountered during the assessment, measuring 33 ft, was 

penetrated by drill hole H-32-H (data point 82, fi g. 3; pl. 1, 

fi g. D) in the southeastern part of this trend, and the Eagle 

No. 5 mine (fi g. 1) extracts coal from a thick coal bed in the 

northwestern part of the trend.

In the eastern part of the coal fi eld, the A coal zone maintains its regional thickness, but the coal zone contains only 

three major coal beds: the Wolf Creek, Wadge, and Lennox, 

in ascending order (pl. 1, fi g. C). These names were probably 

established prior to 1900 because the names were in common 

use by the time they were fi rst mentioned in print in 1906 

(Fenneman and Gale, 1906b). Although the term bed is always 

used when discussing these coals, they almost always comprise several beds. Thus, the term “sub coal zone” seems more 

appropriate and is informally used in this report. Based on 18 

geophysical logs of widely spaced drill holes in this part of 

the coal fi eld, the following information is typical of the sub 

zones.

The stratigraphic distance between the top of the Trout 

Creek Sandstone Member and the base of the Wolf Creek sub 

coal zone ranges from 33 to 76 ft, with an average value of 

about 54 ft. The thickness of the sub zone ranges from 12 to 42 

ft, with an average value of about 22 ft. The sub zone always 

comprises two to four coal beds, with the number of beds 

increasing toward the southeast. The beds range in thickness 

from less than 1 ft to 15 ft, and the stratigraphic position of 

the thinnest and thickest beds within the sub zone appears to 

be random. The stratigraphic distance between the top of the 

Wolf Creek sub coal zone and the base of the Wadge sub coal 

zone ranges from 122 to 145 ft, with an average value of about 

132 ft. The thickness of the sub zone ranges from 11 to 34 

ft, with an average value of about 23 ft. The sub zone always 

comprises two to three coal beds ranging in thickness from 

less than 1 ft to 11 ft. Where the sub zone contains two beds, 

the upper bed is always the thickest, averaging about 8 ft. The 

lower bed lies an average of 9 ft below the upper bed and 

averages about 2 ft thick. Toward the southeast edge of the coal 

fi eld, the sub zone locally picks up a third bed as a rider above 

the other two. This bed lies an average of about 11 ft above 

the upper bed and averages about 2 ft thick . The stratigraphic 

distance between the top of the Wadge sub coal zone and the 

base Lennox sub coal zone ranges from 40 to 58 ft, with an 

average value of about 51 ft. This sub zone typically consists 

of a single coal bed, ranging in thickness from less than 1 ft 

to 4 ft, with an average thickness of about 2 ft. Toward the 

southeast edge of the coal fi eld, a rider bed locally appears 

about 4 ft below the main bed, and this bed averages about 

1 ft thick. One local coal company has defi ned a coal bed positioned between and the Wolf Creek and Wadge sub coal zones 

as the Sage Creek coal bed. This bed might be equivalent to 

a higher-than-normal Wolf Creek bed or a lower-than-normal 

Wadge bed.

The number of coal beds in the A coal zone increases 

in the central part of the coal fi eld. In this area, Bass and 

others (1955) defi ned three coal zones, F, G, and H, which 

are included in the A coal zone used in this assessment. Bass’

terms are seldom used today. In the western part of the coal 

fi eld, the A coal zone contains many coal beds. Here, the Eagle 

and Trapper mines have both developed their own nomenclatures for individual beds. These names are not used in this 

assessment because they are diffi cult to use beyond the mine 

property.

The A coal zone is the most economically important 

coal zone in the coal fi eld, especially in the eastern part. Currently, the Foidel Creek mine (fi g. 1), Seneca II-W mine, and 

Yoast mine extract coal from the Wadge sub coal zone. When 

active, the Seneca II extracted coal from both the Wolf Creek 

and Wadge sub coal zones. Two earlier mines, now closed, 

extracted coal from the A coal zone. The Edna mine extracted 

Geology and Resource Assessment of the Middle and Upper Coal Groups, Yampa Coal Field, Northwestern Colorado P23
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Figure 11. Isopach map of net coal in beds equal to or greater than 1.2 ft thick covering the surface and subsurface extent of the A coal zone, Yampa coal fi e

resource polygon for the A coal zone.
coal from the Wadge sub coal zone, and the Energy mine 

extracted coal from the Wadge and, where feasible, the Lennox 

sub coal zones. The only active mine working the A coal zone 

in the western part of the coal fi eld is the Eagle No. 5 mine, 

which extracts coal from the F and E coal beds, as defi ned by 

Eagle nomenclature.

Barren Interval A

Barren interval A is defi ned as the interval that extends 

from the top of the highest coal bed in the A coal zone to 

the bottom of the lowest coal bed in the B coal zone. The 

interval contains a variety of fl uvial units including thick to 

thin interval of mudrock and sandstone. In the eastern part of 

the coal fi eld, the upper part of the barren interval also contains 

the sub-Twentymile sandstone and, possibly, an underlying 

marine shale unit. In the western part of the coal fi eld, in the 

southern part of the Round Bottom 7.5′ quadrangle, the lower 

part of the barren interval contains a prominent sandstone 

referred to as the unnamed lower sandstone member of the 

Williams Fork Formation by Johnson (1987). Geologists working at the Eagle No. 5 mine, where the sandstone is well 

exposed just above the mine portal, refer to the unit as the 

middle sandstone, in reference to its position midway between 

the Trout Creek Sandstone and the Twentymile Sandstone 

Members. The base of the sandstone lies about 380 ft above 

the top of the Trout Creek, and the unit averages 48 ft in thickness (Johnson, 1987). To the west of this area, the sandstone 

splits into several thinner units, and, to the east, the sandstone 

climbs stratigraphically and then pinches out. In the eastern 

part of the coal fi eld, in the Milner and Rattlesnake Butte 7.5′

quadrangles, the B coal zone is missing and barren interval A 

is defi ned as extending up to the base of the Twentymile. Here, 

barren interval A averages about 721 ft thick. In the central 

part of the coal fi eld, in the Castor Gulch, Breeze Mountain, 

and Hayden Gulch 7.5′ quadrangles, the B coal zone is present 

and begins to thicken toward the west. As a result, the barren 

interval thins in that direction, and, in this area, its thickness 

ranges from 271 ft to 485 ft and averages about 358 ft. In the 

western part of the coal fi eld, in the Horse Gulch and Round 

Bottom 7.5′ quadrangles, the B coal zone continues to thicken 

and the barren interval continues to thin, ranging from 40 ft to 

260 ft and averaging about 116 ft.

B Coal Zone

The B coal zone is defi ned as the interval that extends 

from the bottom of the fi rst coal bed above barren interval A to 

the top of the fi rst coal bed below barren interval B. The coal 

zone is not present in the eastern part of the coal fi eld (pl. 1, 

fi g. C). In the central part of the coal fi eld, the coal zone is 

quite distinct, but in the western part of the coal fi eld barren 

interval A is much thinner, and here separating the A and B 

coal zones can be problematic. The thickness of the B coal 

zone, where present, ranges from 1 ft to 460 ft, with an average 

thickness of about 91 ft.

Of the four coal zones in the Williams Fork Formation, 

the B coal zone displays the most dramatic east-to-west 

increase in the number of coal beds and in the net thickness 

of coal (fi g. 12). In the central part of the coal fi eld, in the 

Breeze Mountain 7.5′ quadrangle, the number of coal beds 

ranges from one to three, with an average of about one. On 

the western side of the coal fi eld, in the Horse Gulch 7.5′

quadrangle, the number of coal beds ranges from two to 15, 

with an average of about seven. In the central part of the coal 

fi eld in the Breeze Mountain 7.5′ quadrangle, the net thickness 

of coal ranges from 3 to 15 ft, with an average thickness of 

about 7 ft. On the western side of the coal fi eld, in the Horse 

Gulch 7.5′ quadrangle, the net thickness of coal ranges from 

13 to 77 ft, with an average of about 33 ft. The number of 

coal beds and the total thickness of coal continues to decrease 

toward the east, and the zone probably pinches out somewhere 

east of the north-central part of the Hayden Gulch 7.5′ quadrangle. The thickest coal bed in the coal zone encountered 

during the assessment, 29 ft, was penetrated by drill hole 

Rb-1-81 in the northern part of the Round Bottom 7.5′ quadrangle (data point 59, fi g. 3).

In the central part of the coal fi eld, the I and J coal beds 

of Bass and others (1955) are within the B coal zone. In the 

western part of the coal fi eld, the Hart bed, a term used by both 

the Eagle and Trapper mines, is within the B coal zone. Two 

small mines have also extracted coal from the B coal zone. In 

the central part of the coal fi eld, the J bed was mined at the 

Searcy mine in Searcy Gulch and about a mile to the east at the 

Jim Dunn mine in Peck Gulch.

Barren Interval B

Barren interval B is defi ned as the interval that extends 

from the top of the highest coal bed in the B coal zone to the 

bottom of the Twentymile Sandstone Member. The lowest part 

of the interval contains a variety of fl uvial units, but most of 

the interval is dominated by marine shale that underlies the 

Twentymile. In the eastern part of the coal fi eld where the 

B coal zone is missing, barren interval B does not exist and 

barren interval A extends up to the bottom of the Twentymile. 

In the central part of the of coal fi eld, where the B coal zone 

is present, the thickness of barren interval B ranges from 82 to 

315 ft, with an average of about 162 ft. The thickness of the 

interval in the western part of the coal fi eld, in the area of the 

Horse Gulch 7.5′ quadrangle, ranges from 4 to 133 ft, with an 

average of about 45 ft. The westward thinning of the interval 

is the result of a thinning of the B coal zone coupled with 

decrease in the amount of marine shale under the Twentymile.

Geology and Resource Assessment of the Middle and Upper Coal Groups, Yampa Coal Field, Northwestern Colorado P25
Figure 12. Isopach map of net coal in beds equal to or greater than 1.2 ft thick covering the surface and subsurface extent of the 

B coal zone, Yampa coal fi eld. Outline is the resource polygon for the B coal zone.

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107 45' 107 30'

T. 6 N.

T. 5 N.

T. 4 N.

T. 7 N.

R 91 W. R 90 W. R 89 W. R 88 W.

R 93 W. R 92 W.

40 30' 

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Data-point location

Thickness isopach

(contour interval 15 ft)

Note: 1.2-ft contour

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30

P26 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
C Coal Zone

The C coal zone is defi ned as the interval that extends 

from the top of the Twentymile Sandstone Member to the top 

of the fi rst coal bed below barren interval C. The coal zone is 

not present in the eastern part of the coal fi eld. The thickness 

of the interval between the base of the lowest coal bed and the 

top of the highest coal bed ranges from 2 ft to 145 ft, with 

an average of about 82 ft. This interval excludes a variable 

thickness of rock that lies above the Twentymile and below the 

lowest coal bed in the C coal zone.

The C coal zone is the least economically signifi cant of 

the four coal zones. The number of coal beds and the net 

thickness of coal (fi g. 13) increases toward the west in the 

same fashion as the B coal zone, only less dramatically. In 

the central part of the coal fi eld, in the Breeze Mountain 7.5′

quadrangle, the number of coal beds ranges from one to six, 

with an average of about three. On the western side of the coal 

fi eld, in the Horse Gulch and Round Bottom 7.5′ quadrangles, 

the number of coal beds ranges from two to eight, with and 

average of about four. In the central part of the coal fi eld, in 

the Breeze Mountain 7.5′ quadrangle, the net thickness of coal 

ranges from 2 to 12 ft, with an average of about 8 ft. On the 

western side of the coal fi eld, in the Horse Gulch and Round 

Bottom 7.5′ quadrangles, the net thickness of coal ranges from 

4 to 27 ft, with an average of about 14 ft. The thickest single 

coal bed in the coal zone encountered during the assessment, 

10 ft, was penetrated by drill hole E-16-HG (data point 33, 

fi g. 3) on the eastern edge of the Horse Gulch 7.5′ quadrangle. 

East of the Breeze Mountain 7.5′ quadrangle, the number of 

coal beds and the net thickness of coal decreases, and the 

zone probably pinches out somewhere east of the north-central 

part of the Hayden Gulch 7.5′ quadrangle. Interestingly, in the 

westernmost part of the coal fi eld, the net thickness of coal 

starts to decrease toward the west (fi g. 13). This phenomena 

might be related to the thinning of the Twentymile as the unit 

becomes more fl uvial toward the west.

In the central part of the coal fi eld, the C coal zone 

contains the K coal bed of Bass and others (1955). In the 

western part of the coal fi eld, both the Eagle and Trapper 

mines have developed their own unique nomenclature for coal 

beds in the C coal zone. These names are not used in this 

assessment because they are diffi cult to use beyond the mine 

property. Other than occasional wagon mines, coal has never 

been extracted from the C coal zone.

Barren Interval C

Barren interval C is defi ned as the interval that extends 

from the top of the highest coal bed in the C coal zone to 

the bottom of the Big White sandstone, or its stratigraphic 

equivalents. In areas where the Big White is missing, the top of 

barren interval B is placed at the bottom of the lowest coal bed 

in the D coal zone. Most of the interval comprises a variety 

of fl uvial units, but if the Big White sandstone is marine, as 

is postulated in this report, then any marine rocks that might 

underlie the sandstone would be included at the top of barren 

interval B. The thickness of the interval where the Big White 

is present ranges from 29 to 183 ft, with an average thickness 

of about 79 ft. In areas where the Big White is absent, the 

interval is about 20 ft thicker than its regional average. On the 

eastern side of the coal fi eld, in areas where the C coal zone is 

missing, the bottom of the interval is defi ned as the top of the 

Twentymile Sandstone Member.

D Coal Zone

The D coal zone is defi ned as the interval that extends 

from the top of the Big White sandstone, or its stratigraphic 

equivalents, to the top of the Williams Fork Formation. In 

areas where the Big White is missing, the base is defi ned at 

the bottom of the fi rst coal bed above barren interval C. In 

the western part of the coal fi eld, the coal zone includes the 

Three White sandstones in the upper part of the Williams Fork. 

The thickness of the interval that extends from the base of the 

lowest coal bed to the top of the highest coal bed ranges from 

4 ft to 815 ft, with an average of about 355 ft. This interval 

excludes rock that lies above the Big White sandstone, where 

present, and below the lowest coal bed in the coal zone. In the 

eastern part of the coal fi eld, the Lewis Shale rests directly on 

the only coal bed assigned to the D coal zone. The interval 

between the top of the highest coal bed in the coal zone and the 

top of the Williams Fork ranges from 0 ft in the eastern part of 

the coal fi eld to 277 ft in the western part of the coal fi eld. The 

wide range in thickness is explained by the fact that the Lewis 

climbs stratigraphically toward the west, allowing for a thicker 

section of the Williams Fork. 

The D coal zone is the second most economically important coal zone in the Williams Fork, especially in the western 

part of the coal fi eld. The number of coal beds and the net 

thickness of coal (fi g. 14) increases toward the west in the 

same fashion as the B and C coal zones. In the east-central part 

of the coal fi eld, in the Hayden 7.5′ quadrangle, the number 

of coal beds ranges from one to seven, with an average of 

about four. On the western side of the coal fi eld, in the Horse 

Gulch and Round Bottom 7.5′ quadrangles, the number of coal 

beds ranges from seven to 16, with an average of about 12. 

In the east-central part of the coal fi eld, in the Hayden 7.5′

quadrangle, the net thickness of coal ranges from 4 to 22 ft, 

with an average of about 14 ft. On the western side of the coal 

fi eld, in the Horse Gulch and Round Bottom 7.5′ quadrangles, 

the net thickness of coal ranges from 24 to 52 ft, with an 

average of about 38 ft. East of the Hayden 7.5′ quadrangle, the 

number of coal beds and the net thickness of coal continues 

to decrease to the point where the coal zone contains only 

one coal bed. The thickest single coal bed in the coal zone 

encountered during this assessment, 14 ft, was penetrated by 

drill hole H-36-H (data point 79, fi g. 3) in the central part of 

the Hamilton 7.5′ quadrangle. In the eastern part of the coal 

fi eld, only the Fish Creek coal bed (Campbell, 1923) is present 

Geology and Resource Assessment of the Middle and Upper Coal Groups, Yampa Coal Field, Northwestern Colorado P27
Figure 13. Isopach map of net coal in beds equal to or greater than 1.2 ft thick covering the surface and subsurface extent of the C 

coal zone, Yampa coal fi eld. Outline is the resource polygon for the C coal zone.

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107 45' 107 30'

T. 6 N.

T. 5 N.

T. 4 N.

T. 7 N.

R 91 W. R 90 W. R 89 W. R 88 W.

R 93 W. R 92 W.

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(contour interval 5 ft)

Note: 1.2-ft contour

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P28 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
in the D coal zone (pl. 1, fi g. B). Bass and others (1955) 

did not mention the Fish Creek, but their Dry Creek coal bed 

in the east-central part of the coal fi eld is at about the same 

stratigraphic level as the Fish Creek, and the two coal beds 

might be equivalent. In the central part of the coal fi eld, the 

D coal zone contains the L, M, N, O, P, R, and S coal beds 

of Bass and others (1955). The coal beds mined in this area at 

the Carey and Sleepy Cat mines (Bass and others, 1955) are 

probably within the D coal zone. In the western part of the 

coal fi eld, the Eagle and Trapper mines have both developed 

their own nomenclature for individual beds in the D zone, 

although Eagle’s nomenclature is similar to that used by Bass 

and others in the central part of the coal fi eld. The names used 

by the Eagle and Trapper mines are not used in the assessment 

because they are diffi cult to use beyond the mine property. In 

the eastern part of the coal fi eld, the Fish Creek coal bed was 

mined, where economically feasible, at the now-abandoned 

Energy mine. In the central part of the coal fi eld, coal from 

the D zone was mined at the Carey and Sleepy Cat mines 

(underground). In the western part of the coal fi eld, the Trapper mine extracts coal from the R, Q, M, L, I, and H beds, 

as defi ned by Trapper’s nomenclature. In this same area, the 

Eagle No. 9 mine extracts coal from the P bed, as defi ned by 

Eagle’s nomenclature.

Coal Quality

Most Cretaceous coal in the Yampa coal fi eld is noncoking, high-volatile C bituminous, but some subbituminous A, B, 

and C is reported. Rare anthracite is also present adjacent to 

certain Tertiary igneous intrusions in the northeastern part of 

the coal fi eld (Bass and others, 1955). Coal analyses from the 

eastern part of the coal fi eld, on an as-received basis, return 

average values of 9.4 percent moisture, 41.1 percent volatile 

matter, 51.8 percent fi xed carbon, 6.9 percent ash yield, 0.9 

percent sulfur content, and an average caloric value of 11,580 

Btu/lb. Coal analyses from the western part of the coal fi eld, 

on an as-received basis, return average values of 11.6 percent 

moisture, 42.0 percent volatile matter, 53.8 percent fi xed 

carbon, 4.3 percent ash yield, 0.3 percent sulfur content, and 

an average caloric value of 11,500 Btu/lb (Speltz, 1976).

Summarizing coal analyses contained in a USGS database of specifi c coal beds in the A coal zone in the eastern 

part of the coal fi eld (R.H. Affolter, written commun., 1999), 

the Wolf Creek bed has average as-received values of 10.90 

percent ash yield and 0.72 percent sulfur content, and an 

average caloric value of 10,769 Btu/lb. The Wadge bed has 

average values of 7.97 percent ash yield and 0.58 percent 

sulfur content, and an average caloric value of 11,192 Btu/lb. 

The Lennox bed has average values of 6.73 percent ash yield, 

2.64 percent sulfur content, and an average caloric value of 

11,422 Btu/lb. Little information is available on the quality of 

coal in the A coal zone in the western part of the coal fi eld, 

but as-received data provided by personnel at the Eagle No. 

5 mine to Zook and Tremain (1997) lists Eagle’s F bed as 

subbituminous B, with a range for ash yield between 4.99 and 

10.36 percent and a range for sulfur content between 0.46 to 

0.57 percent. The caloric value is reported to range between 

10,377 and 11,567 Btu/lb, and the coal is a mixture of subbituminous A, B, and C, and high-volatile bituminous C. The 

only other coal zone that is presently being mined in the coal 

fi eld is the D zone in the western part of the coal fi eld. According to personnel at the Trapper mine, the eight beds currently 

being extracted are a mixture of subbituminous A, B, and C, 

and high-volatile bituminous C. Average, as-received values 

for all of the beds mined during September 1998 are ash yield 

7.05 percent and sulfur content 0.40 percent, with a caloric 

value of 9,931 Btu/lb.

Coal Resources

In essence, coal resources are calculated by multiplying 

thickness by areal extent to acquire volume, and then multiplying this value by density to obtain tonnage. However, in detail 

the process of calculating resources is quite involved. Because 

of the poor quality of many of the geophysical logs used in this 

assessment, the thickness of coal beds penetrated by public 

drill holes was measured only to the nearest foot. However, 

some proprietary databases used in the assessment have coal 

beds measured to the nearest tenth of a foot. Following the 

methodology of Wood and others (1983), non-coal partings 

within a coal bed that did not exceed the thickness of the coal 

layer directly above or below were deleted for the purpose of 

resource calculations. To accomplish this, a computer program 

developed by the USGS was used to delete the parting and 

combine the adjacent parts of coal beds. In selecting data 

for use in resource calculations, only those drill holes that 

penetrated the entire thickness of a given coal zone were used. 

That is, holes that were commenced below the top of the zone 

or were completed above the bottom of the zone were not 

used.

The maximum polygon used in calculating coal resources 

(e.g., fi g. 2) was constructed using the outcrop of the top of 

the Trout Creek Sandstone Member of the Iles Formation as 

the west, south, and east sides, and arbitrary township lines 

on the north side. The west side of the northern boundary 

was drawn along the top of T. 7 N., and the east side of the 

boundary was drawn along the top of T. 6 N. North of this line, 

subsurface data are sparse but the Williams Fork Formation 

is undoubtedly deeper than 6,000 ft, which is the economic 

cut-off suggested by Wood and others (1983). This resource 

polygon includes all areas traditionally included in the coal 

fi eld (e.g., fi g. 1) except for the north-trending extension in the 

eastern part of the coal fi eld. This northeastern part of the coal 

fi eld was terminated against the T. 6 N. line because, to the 

north, the exact location of the Trout Creek Member is somewhat uncertain and because the steep geologic structure (fi g. 

9) would probably preclude mining. The maximum resource 

polygon covers about 630 mi2

 (fi g. 2), whereas the area of 

the coal fi eld based on the surface exposure of the Mesaverde 

Geology and Resource Assessment of the Middle and Upper Coal Groups, Yampa Coal Field, Northwestern Colorado P29
Figure 14. Isopach map of net coal in beds equal to or greater than 1.2 ft thick covering the surface and subsurface extent of the D coal 

zone, Yampa coal fi eld. Outline is the resource polygon for the D coal zone.

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T. 6 N.

T. 5 N.

T. 4 N.

T. 7 N.

R 88 W.

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Data-point location

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P30 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Group covers only 520 mi2

 (fi g. 1). This difference results 

from (1) the polygon not including the Iles Formation, and (2) 

the polygon extending north of the north-dipping stratigraphic 

top of the Williams Fork into areas where the formation is 

not exposed at the surface. It should be noted that the coalbearing Lance and Fort Union Formations could be included 

in a broader defi nition of the coal fi eld, but, traditionally, only 

the Mesaverde is taken into account. For each of the four 

coal zones, areas covered by active coal leases (provided by 

the BLM), or areas known to have been mined out (provided 

by the Colorado Geological Survey), were eliminated from 

resource calculations. In regard to coal leases, if the company 

had a specifi c bed under lease then the entire zone containing 

the bed was eliminated. In those cases where the company had 

all of the coal under lease, all four zones where eliminated.

Using the methodology of Wood and others (1983), coal 

tonnages were calculated by multiplying the estimated volume 

of coal by the average density. The volume of coal is the 

product of net-coal thickness and areal extent. The areal extent 

of the A and B coal zones was determined by utilizing structure contours drawn on top of the Trout Creek (fi g. 9), the 

base elevation of the zone above the Trout Creek, and the 

1:250,000-scale digital elevation model (DEM) constructed by 

the USGS. In the case of the C and D coal zones, structure 

contours drawn on top of the Twentymile Sandstone Member 

of the Williams Fork were used. Where a coal zone is partly 

eroded, calculations were stopped at the zero overburden line. 

An average apparent rank of bituminous coal was used, based 

on published analyses and discussions with mine personnel. 

The average density of bituminous coal is 1.32 g/cm3

 or 1,800 

short tons per acre foot, as recommended by Wood and others 

(1983). Resources are reported as net coal, which is the sum 

of all coal beds equal to or greater than 1.2 ft thick. Beds 

thinner than this were considered uneconomic by Wood and 

others. Following Wood and others, resources are reported 

in reliability categories of identifi ed or hypothetical, based 

on the distance that the resource was calculated from a data 

point. Resources reported as identifi ed are located within a 

3-mi radius of a data point and have a higher degree of geologic assurance, and those reported as hypothetical are located 

beyond a 3-mi radius and have a lower degree of geologic 

assurance. Included within the identifi ed reliability category 

are the measured, indicated, and inferred categories, but these 

subdivisions were not used in this assessment. Maximum overburden was determined by subtracting the elevations at the 

base of each coal zone from the surface elevations imported 

from the DEM. Resources are reported in maximum overburden categories of 0–500 ft; 500–1,000 ft; 1,000–2, 000 ft; 

2,000–3,000 ft; and greater that 3,000 ft. Nowhere in the 

resource polygon does the maximum overburden exceed 6,000 

ft. These categories were generated by integrating the maximum overburden and net-coal isopach maps of each coal zone. 

In order to better understand the distribution of coal, maps 

were constructed for each coal zone that show net coal in 

fi ve net-thickness categories: 1.2–2.3 ft, 2.3–3.5 ft, 3.5–7.0 

ft, 7.0–14.0 ft, and greater that 14.0 ft. Only the B and C 

coal zones have entries in all fi ve net-thickness categories. 

The D coal zone has only three of the fi ve categories because 

nowhere in the coal fi eld is the net-coal thickness less than 

3.5 ft, and the A coal zone has only one of the fi ve because 

nowhere in the coal fi eld is the net-coal thickness less than 

14.0 ft. The coal resource for each of the four coal zones is 

reported in tables for areas within Moffat and Routt Counties, 

and for each 7.5′ quadrangle and for each township (Appendix 

3, Appendix 4, Appendix 5, and Appendix 6).

Coal resource numbers cited in the assessment have been 

rounded to two signifi cant fi gures. It is extremely important 

to keep this in mind when examining the numbers provided 

in Appendixes 3, 4, 5, and 6 of this report because totals 

might not equal the sum of their components in any particular 

column because of independent rounding. The actual procedures used to generate the resource numbers in this assessment 

are extensive and complex. Those interested in these details 

should refer to Roberts and others (1998) and Roberts and 

Biewick (1999).

The reader should be aware that certain systematic errors 

can signifi cantly infl uence fi nal resource estimates for a given 

coal fi eld. Errors in preparing the raw data include the diffi culty in differentiating between coal and carbonaceous shale 

on some geophysical logs, and the fact that bed thickness when 

determined from the geophysical curves can vary depending 

on whether the midpoint or the infl ection point is used (the 

midpoint was used in this assessment). Another source of 

error is introduced by using a single coal rank to represent an 

entire coal fi eld, and then accepting an average density for that 

rank. But the biggest source of error occurs during the actual 

calculation of the resources. The computer program assumes 

that a given coal bed is continuous between data points and 

that any change in thickness is uniform. Because of the nature 

of Cretaceous coals in the Rocky Mountains, this is rarely the 

case, and considerable error is probably introduced because of 

this assumption.

A Coal Zone

The A coal zone contains an estimated 42 billion short 

tons of net coal in beds equal to or greater than 1.2 ft thick 

(Appendix 3a). Of this, about half is classifi ed as identifi ed 

and the other half hypothetical. Resources in net-coal thickness 

categories are not listed in Appendix 3a, nor is a fi gure of coalthickness categories provided because net coal in the A zone 

is everywhere greater than 14 ft thick. Resources in maximum 

overburden categories are listed in Appendix 3a and shown 

on fi gure 15. Moffat County contains about 70 percent of the 

A coal zone resource, with the remaining amount in Routt 

County, (Appendix 3a). Private land overlies about 93 percent 

the of the A-zone coal, but about 67 percent of the A-zone 

coal is owned by the Federal Government (Appendixes 3b 

and 3c). Resources for the A coal zone are listed for each 

7.5′ quadrangle and for each township in the coal fi eld (Appendixes 3d and 3e).

Geology and Resource Assessment of the Middle and Upper Coal Groups, Yampa Coal Field, Northwestern Colorado P31
The A coal zone contains more coal than the other three 

zones combined. Much of this coal underlies Moffat County, 

but the only mine in the area that recently extracted A-zone 

coal is currently closed. Nevertheless, the western part of 

the coal fi eld will probably witness increased exploration, leasing, and development of this resource in the future. The eastern part of the coal fi eld in Routt County contains a lesser 

volume of A-zone coal, but two signifi cant beds, the Wolf 

Creek and Wadge, are currently being extracted from three 

mines. Because these mines are already established, this part 

of the coal fi eld is likely to produce most of the A-zone coal, 

at least in the short term.

B Coal Zone

The B coal zone contains an estimated 13 billion short 

tons of net coal in beds equal to or greater than 1.2 ft thick 

(Appendix 4a). Of this, about 40 percent is classifi ed as identifi ed, with the remaining amount being hypothetical. Resources 

in net-coal thickness categories are listed in Appendix 4a

and shown on fi gure 16. Resources in maximum overburden 

categories are listed in Appendix 4a and shown on fi gure 

17. Moffat County contains almost all of the B coal zone 

resource (Appendix 4a). Private land overlies about 85 percent 

of the B-zone coal, but about 75 percent of the B-zone coal 

is owned by the Federal Government (Appendixes 4b and 4c). 

Resources for the B coal zone are listed for each 7.5′ quadrangle and for each township in the coal fi eld (Appendixes 4d 

and 4e).

Although the B coal zone contains only a moderate 

amount of coal, which is limited to the western part of the 

coal fi eld, several beds in the coal zone are thick and laterally 

extensive. Perhaps the most promising area for development 

is the Hart syncline (fi g. 10) where bed thickness commonly 

exceeds 20 ft and overburden is relatively thin (fi g. 17). Unfortunately, the deposit is confi ned to a small area, which limits 

the amount of coal that can ultimately be extracted.

C Coal Zone

The C coal zone contains an estimated 3.7 billion short 

tons of net coal in beds equal to or greater than 1.2 ft thick 

(Appendix 5a). Of this, about half is classifi ed as identifi ed 

and the other half hypothetical. Resources in net-coal thickness 

categories are listed in Appendix 5a and shown on fi gure 18. 

Resources in maximum overburden categories are listed in 

Appendix 5a and shown on fi gure 19. Moffat County contains 

about 86 percent of the C coal zone resource, with the remaining amount in Routt County (Appendix 5a). Private land overlies about 92 percent the of the C-zone coal, but about 73 

percent of the C-zone coal is owned by the Federal Government (Appendixes 5b and 5c). Resources for the C coal zone 

are listed for each 7.5′ quadrangle and for each township in the 

coal fi eld (Appendixes 5d and 5e).

The C coal zone contains substantially less coal than 

any of the other three zones. Although it does contains some 

locally thick coal beds, the zone should not be considered an 

economic entity for the foreseeable future. The coal zone was 

only included to complete the coal assessment of the Williams 

Fork Formation.

D Coal Zone

The D coal zone contains an estimated 17 billion short 

tons of net coal in beds equal to or greater than 1.2 ft thick 

(Appendix 6a). Of this, about 40 percent is classifi ed as identifi ed, with the remaining amount being hypothetical. Resources 

in net-coal thickness categories are listed in Appendix 6a and 

shown on fi gure 20. Resources in maximum overburden cateegories are listed in Appendix 6a and shown on fi gure 21. 

Moffat County contains about 88 percent of the D coal zone 

resource, with the remaining amount in Routt County (Appendix 6a). Private land overlies nearly 100 percent the of the 

D-zone coal, but about 70 percent of the D-zone coal is 

owned by the Federal Government (Appendixes 6b and 6c). 

Resources for the D coal zone are listed for each 7.5′ quadrangle and for each township in the coal fi eld (Appendixes 6c 

and 6d).

The D coal zone is the second most productive coal zone 

in the coal fi eld, although it contains only about one-third of 

the coal present in the A coal zone. Most of the D-zone coal 

underlies Moffat County, and the only operating mine in the 

area extracts coal from this zone. With little doubt, most coal 

exploration, leasing, and development in the western part of 

the coal fi eld will continue to be from this coal zone. Although 

D-zone coal in the eastern part of the coal fi eld, the Fish Creek 

bed, has been mined in the past, its thinness and high sulfur 

content make it uneconomic.

Restrictions to Coal Availability

Certain technical restrictions limit the mining of coal 

underground (T. J. Rohrbacher, oral commun., 1999). The 

three main issues are coal-bed thickness, bed inclination, and 

bed depth. Under current mining practices, coal beds thinner 

than about 2 ft cannot be recovered. And, no more than 14 ft 

of coal can usually be recovered from a bed of any thickness. 

Hypothetically, all of a 14 ft bed can be recovered, but only 

14 ft of a 20 ft bed can be recovered. Underground mining is 

most effective where the bed is inclined less than 6 degrees 

and is very diffi cult where the bed is inclined greater that 12 

degrees. And fi nally, underground mining rarely takes place 

deeper than 3,000 ft. Restrictions that limit surface mining 

are more economic than technical. Under current conditions, 

stripping ratios (overburden to coal) should be less than 10:1 

in order to insure a profi t.

Land-use restrictions can limit coal availability. For 

example, coal resources that underlie cultural features such 

P32 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
R 88 W. R 87 W. 

R 91 W. R 90 W. R 89 W.

R 93 W. R 92 W.

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Figure 15. Isopach map of maximum overburden to the base of the A coal zone, Yampa coal fi eld.
Figure 16. Net-coal thickness categories for the B coal zone, Yampa coal fi eld.

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T. 5 N.

T. 4 N.

T. 7 N.

R 91 W. R 89 W. R 88 W.

R 93 W. R 92 W.

0 5 mi

107 45' 107 30'

40 30' 

40 15' 

R 90 W.

● Data-point location

2.3-3.5 ft

1.2- 2.3 ft

3.5-7.0 ft

7.0-14.0 ft

>14.0 ft

P34 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Figure 17. Isopach map of maximum overburden to the base of the B coal zone, Yampa coal fi eld. 

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T. 5 N.

T. 4 N.

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R 91 W. R 89 W. R 88 W.

R 93 W. R 92 W.

● Data-point location

0-500 ft

500-1000 ft

1000-2000 ft

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> 3000 ft

0 5 mi

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R 90 W.

Geology and Resource Assessment of the Middle and Upper Coal Groups, Yampa Coal Field, Northwestern Colorado P35
Figure 18. Net-coal thickness categories for the C coal zone, Yampa coal fi eld.

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T. 7 N.

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R 91 W. R 90 W. R 89 W. R 88 W.

R 93 W. R 92 W.

● Data-point location

1.2- 2.3 ft

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>14.0 ft

2.3-3.5 ft

0 5 mi

107 45' 107 30'

40 30' 

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P36 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Figure 19. Isopach map of maximum overburden to the base of the C coal zone, Yampa coal fi eld.

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T. 4 N.

R 91 W. R 90 W. R 89 W. R 88 W.

R 93 W. R 92 W.

● Data-point location

0-500 ft

500-1000 ft

1000-2000 ft

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> 3000 ft

0 5 mi

107 45' 107 30'

40 30' 

40 15' 

Geology and Resource Assessment of the Middle and Upper Coal Groups, Yampa Coal Field, Northwestern Colorado P37
Figure 20. Net-coal thickness categories for the D coal zone, Yampa coal fi eld.

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40 15' 

107 30'

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T. 6 N.

T. 5 N.

T. 4 N.

T. 7 N.

R 88 W.

R 91 W. R 90 W. R 89 W.

R 93 W. R 92 W.

● Data-point location

3.5-7.0 ft

7.0-14.0 ft

>14.0 ft

0 5 mi

P38 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Figure 21. Isopach map of maximum overburden to the base of the D coal zone, Yampa coal fi eld.

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T. 5 N.

T. 4 N.

T. 7 N.

40 15' 

107 30'

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107 45'

● Data-point location

0-500 ft

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1000-2000 ft

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> 3000 ft

0 5 mi

Geology and Resource Assessment of the Middle and Upper Coal Groups, Yampa Coal Field, Northwestern Colorado P39
as towns and highways are unavailable for extraction. Environmental restrictions can also limit coal availability. For example, coal resources adjacent to a wildlife habitat such as raptor 

nests might not be available for extraction. Air and water quality are always issues of concern in areas where coal is either 

mined or burned, and, in the case of the Yampa coal fi eld, both 

of are occurring. There is always the possibility that future 

increases in coal production and utilization in this region might 

be limited because of these issues. For example, in the past few 

years the burning of coal in the Yampa Valley has caused some 

concern in regard to acid rain in the nearby Routt National 

Forest. Although this and other environmental problems could 

be lessened by mitigation, they still might limit the amount of 

coal that can be ultimately recovered.

Summary of Coal Resources

The Yampa coal fi eld contains an estimated net coal 

resource of about 76 billion short tons in beds equal to or 

greater than 1.2 ft. This is more coal than the combined 

resources of northwest Colorado’s other two coal fi elds, the 

Danforth Hills north of Meeker and the Lower White River 

north of Rangely. Coal classifi ed as identifi ed makes up about 

46 percent, with the remaining 54 percent classifi ed as hypothetical. Most of the hypothetical coal lies deep below the 

ground surface in the northern part of the maximum resource 

polygon (fi g. 2).

Although there is a signifi cant amount of coal in the coal 

fi eld, this fi gure should be regarded with caution because it 

does not refl ect geologic, land-use, and environmental restrictions that might limit coal availability. For example, of the 

76 billion short tons, about 48 percent is under more than 

3,000 ft of overburden and thus is unavailable for underground 

mining. In addition, coal beds that dip more than 12 degrees 

are unavailable for underground mining at any depth, and such 

resources in the vicinity of the Sage Creek, Fish Creek, and 

Tow Creek anticlines (fi g. 10) are considerable. But even more 

signifi cant, about 90 percent of the coal is under more than 500 

ft of overburden and is thus unavailable for surface mining. 

In addition, the coal in beds greater than 14 ft thick would 

be left behind in underground mines and subeconomic coal 

beds would be wasted during surface mining. An estimate 

of the amount of coal that would be subtracted from the netcoal resource for land-use and environmental concerns would 

require a detailed coal availability study of the entire coal fi eld, 

but suffi ce it to say that the deduction would be signifi cant. To 

conclude, only a small percentage of the 76 billion short tons 

of the net-coal resource could be recovered.

Moffat County contains about 80 percent of the net-coal 

resource in the coal fi eld. This is of interest to the county 

because future mining operations would undoubtedly contribute signifi cantly to the tax base. About 93 percent of the total 

net-coal resource in the coal fi eld underlies private surface. 

This is of interest to land owners because, as new mines 

are developed, compensation for loss of acreage and for disturbance would provide vital income at a time when farming is 

not as profi table as it once was. About 69 percent of the netcoal resource is owned by the Federal Government (fi g. 22). 

This is important to the Nation because royalties paid on coal 

leases provide a source of revenue to the Government.

The future of coal mining in northwestern Colorado 

appears bright. The industry will continue to support the local 

economy by providing jobs and by purchasing goods and 

services from local suppliers. However, during the next decade 

most of the coal produced in the coal fi eld will come from 

areas presently under lease and from coal mines already in 

existence. The A coal zone will continue to dominate production in the eastern part of the fi eld, and the D coal zone will 

continue to dominate in the western part of the coal fi eld. Coal 

mining in the Yampa coal fi eld, combined with coal mining 

in the Danforth Hills and Lower White River coal fi elds, will 

remain an important social and economic factor in this region 

of Colorado well into the 21st century.

P40 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Federal

Non-Federal (State and private)

Coal Ownership

T. 7 N.

R 88 W. R 87 W. 

R 91 W. R 90 W. R 89 W.

R 93 W. R 92 W.

107 30' 

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Figure 22. Federal and non-Federal coal ownership in the Yampa coal fi eld. 
Selected References

Adair, J.S., 1952, Geology of a portion of the Yampa coal fi eld, Routt 

County, Colorado: U.S. Geological Survey unnumbered map, scale 

1:31,680.

Bader, J.W., 1983, Section A-A′, subsurface correlations of some 

Upper Cretaceous and Tertiary rocks from the Cherokee Ridge, 

Wyoming, to the southeast fl ank of the Sandwash Basin, Colorado: 

U.S. Geological Survey Open-File Report 83-0362.

Bader, J.W., Gill, J.R., Cobban, W.A., and Law, B.E., 1983, Biostratigraphic correlation chart of some Upper Cretaceous rocks from 

the Lost Soldier area, Wyoming to west of Craig, Colorado: U.S. 

Geological Survey Miscellaneous Field Studies Map MF-1548.

Bass, N.W., Eby, J.B., and Campbell, M.R., 1955, Geology and mineral 

fuels of parts of Routt and Moffat Counties, Colorado: U.S. Geological Survey Bulletin 1027-D, p. 143–250.

Boreck, D.L., Jones, D.C., Murray, D.C., Schultz, J.E., and Suek, D.C., 

1977, Colorado coal analyses, 1975: Colorado Geological Survey 

Information Series 7.

Boreck, D.L., and Murray, D.K., 1979, Colorado coal reserve depletion 

data and coal mine summaries: Colorado Geological Survey OpenFile Report 79-1, 65 p.

Boyles, M.J., Kauffman, E.G., Kiteley, L.W., and Scott, A.J., 1981, Depositional systems Upper Cretaceous Mancos Shale and Mesaverde 

Group, northwestern Colorado: Society of Economic Paleontologists and Mineralogists, Rocky Mountain Section, Field Trip Guidebook, 146 p.

Bronson, R.J., 1979, Reconnaissance drill hole in the Yampa coal fi eld, 

Routt County, Colorado: U.S. Geological Survey Open-File Report 

79-1593, 3 p.

Brownfi eld, M.E., 1976, Geophysical logs of seventeen holes drilled in 

1976 in the Yampa coal fi eld, northwestern Colorado: U.S. Geological Survey Open-File Report 76-817, 4 p.

Brownfi eld, M.E., 1978a, Reconnaissance drilling during 1976 in Rattlesnake Butte quadrangle, Routt County, Colorado: U.S. Geological 

Survey Open-File Report OF 78-364, 11 p.

Brownfi eld, M.E., 1978b, Reconnaissance drilling during 1977 in the 

Yampa coal fi eld, Moffat and Routt Counties, Colorado: U.S. Geological Survey Open-File Report OF 365, 135 p.

Brownfi eld, M.E., and Anderson, K., 1979, Geologic map and coal 

sections of the Lay SE quadrangle, Moffat County, Colorado: U.S. 

Geological Survey Open-File Report 79-1680, scale 1:24,000.

Brownfi eld, M.E., and Johnson, E.A., 1986, A regionally extensive 

altered air-fall ash for use in correlation of lithofacies in the Upper 

Cretaceous Williams Fork Formation, northwestern Piceance Creek 

and southern Sand Wash Basin, Colorado, in Stone, D.S., ed., New 

Interpretations of Northwest Colorado Geology: Rocky Mountain 

Association of Geologists, p. 165–169.

Brownfi eld, M.E., and Prost, G.L., 1979, Geologic map and coal sections of the Lay quadrangle, Moffat County, Colorado: U.S. Geological Survey Open-File Report 79-1679, scale: 1:24,000.

Campbell, M.R., 1906, Character and use of Yampa coals, in Fenneman, 

N.M., and Gale, H.S., The Yampa Coal Field, Routt County, Colorado: 

U.S. Geological Survey Bulletin 297, p. 82–91.

Campbell, M.R., 1912, Miscellaneous analyses of coal samples from 

various fi elds of the United States: U.S. Geological Survey Bulletin 

471-J, p. 629–655.

Campbell, M.R., 1923, The Twentymile Park district of the Yampa coal 

fi eld, Routt County, Colorado: U.S. Geological Survey Bulletin 748, 

82 p.

Chisholm, F.F., 1887, The Elk Head anthracite coal fi eld of Routt County, 

Colorado: Proceedings of the Colorado Scientifi c Society, v. 2, p. 

147–149.

Cobban, W.A., and Reeside, J.B., Jr., 1952, Correlation of the Cretaceous formations of the Western Interior of the United States: 

Geological Society of America Bulletin, v. 63, p. 1011–1044. 

Collins, B.A., 1976, Coal deposits of the Carbondale, Grand Hogback, 

and southern Danforth Hills coal fi eld, eastern Piceance Basin, 

Colorado: Quarterly of the Colorado School of Mines, v. 71, no. 1, 

138 p.

Colorado State Planning Commission, 1939, Oak Creek and Mt. Harris 

coal fi elds, Routt County, Colorado, scale 1:63,360.

Craise, F.A., 1910, Taking coal from fi ve western veins by one opening: 

Black Diamond, December 31, p. 16. 

Crawford, R.D., Willson, K.W., and Perini, V.C., 1920, Some anticlines 

of Routt County, Colorado: Colorado Geological Survey, Bulletin 23, 

59 p.

Cullins, H.L., 1971, Geologic map of the Rangely quadrangle, Rio 

Blanco County, Colorado: U.S. Geological Survey Geologic Quadrangle Map GQ-903, scale 1:24,000.

Dames and Moore, compiler, 1978a, Coal resource occurrence and 

coal development potential maps of the Wolf Mountain quadrangle, 

Routt County, Colorado: U.S. Geological Survey Open-File Report 

78-624, 28 p., 11 oversized sheets, scale 1:24,000.

Dames and Moore, compiler, 1978b, Coal resource occurrence and 

coal development potential maps of the Hooker Mountain quadrangle, Routt County, Colorado: U.S. Geological Survey Open-File 

Report 78-626, 21 p., 13 oversized sheets, scale 1:24,000.

Dames and Moore, compiler, 1978c, Coal resource occurrence and 

coal development potential maps of the Craig quadrangle, Moffat 

County, Colorado: U.S. Geological Survey Open-File Report 78-627, 

15 p., 4 oversized sheets, scale 1:24,000.

Dames and Moore, compiler, 1978d, Coal resource occurrence and 

coal development potential maps of the Cow Creek quadrangle, 

Routt County, Colorado: U.S. Geological Survey Open-File Report 

78-629, 21 p., 14 oversized sheets, scale 1:24,000.

Dames and Moore, compiler, 1979a, Coal resource occurrence and 

coal development potential maps of the Monument Butte quadrangle, Moffat County, Colorado: U.S. Geological Survey Open-File 

Report 79-281, 19 p., 8 oversized sheets, scale 1:24,000.

Dames and Moore, compiler, 1979b, Coal resource occurrence and 

coal development potential maps of the Hamilton quadrangle, 

Moffat County, Colorado: U.S. Geological Survey Open-File Report 

79-628, 32 p., 43 oversized sheets, scale 1:24,000.

P42 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Dames and Moore, compiler, 1979c, Coal resource occurrence and 

coal development potential maps of the Pine Ridge quadrangle, 

Moffat County, Colorado: U.S. Geological Survey Open-File Report 

79-876, 27 p., 27 oversized sheets, scale 1:24,000.

Dames and Moore, compiler, 1979d, Coal resource occurrence and 

coal development potential maps of the Lay quadrangle, Moffat 

County, Colorado: U.S. Geological Survey Open-File Report 79-877, 

28 p., 22 oversized sheets, scale 1:24,000.

Dames and Moore, compiler, 1979e, Coal resource occurrence and 

coal development potential maps of the Lay SE quadrangle, Moffat 

County, Colorado: U.S. Geological Survey Open-File Report 79-878, 

31 p., 44 oversized sheets, scale 1:24,000.

Dames and Moore, compiler, 1979f, Coal resource occurrence and 

coal development potential maps of the Rock Springs Gulch 

quadrangle, Moffat and Routt Counties, Colorado: U.S. Geological 

Survey Open-File Report 79-876, 18 p., 8 oversized sheets, scale 

1:24,000.

Dames and Moore, compiler, 1979g, Coal resource occurrence and 

coal development potential maps of the Ralph White Lake quadrangle, Moffat and Routt Counties, Colorado: U.S. Geological Survey 

Open-File Report 79-880, 23 p., 8 oversized sheets, scale 1:24,000.

Dames and Moore, compiler, 1979h, Coal resource occurrence and 

coal development potential maps of the Juniper Hot Springs quadrangle, Moffat County, Colorado: U.S. Geological Survey Open-File 

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Appendix 1—Metric Conversion Factors

Metric conversion factors. 

 Customary inch-pound units SI conversion 

 acre ............................................................................ 4,046.87 square meters 

 acre-foot..................................................................... 1,233.49 cubic meters 

 British thermal unit (Btu) .......................................... 1,005.056 joules 

 British thermal unit / pound (Btu / lb) ....................... 2,326 joules / kilogram 

 foot (ft) ...................................................................... 0.3048 meters 

 inch (in) ..................................................................... 0.0254 meters 

 mile (mi) .................................................................... 1.609 kilometers 

 pound (lb) .................................................................. 0.4536 kilograms 

 short ton (ton) ............................................................ 0.9072 metric tons 

 short tons / acre-foot.................................................. 0.7355 kilograms / cubic meter 

 square mile (mi2

)........................................................ 2.59 square kilometers 

Geology and Resource Assessment of the Middle and Upper Coal Groups, Yampa Coal Field, Northwestern Colorado P47
Surface Total Top of Trout Map Point ID Source Longitude Latitude Section Township Range elevation depth Creek Sandstone Total Total Total 

no. (ft) (ft) elev. (ft) coal (ft) # beds coal (ft) # beds coal (ft) # beds 

1 JHS-1-81C 85-37 -107.88328 40.48542 7 T6N R93W 6,450 632 17 3 2 R-1-JHS 85-43 -107.87895 40.48659 7 T6N R93W 6,440 742 5,765 78 23 13 2 3 R-2-JHS 85-43 -107.87787 40.47223 18 T6N R93W 6,494 961 5,882 54 10 4 Y-4 76-383 -107.87664 40.49306 6 T6N R93W 6,418 740 5,716 90 15 22 5 5 Y-18-HG 76-817 -107.87208 40.47783 18 T6N R93W 6,565 1,200 5,420 69 18 41 8 4 2 6 Y-13-HG 76-817 -107.86686 40.45519 19 T6N R93W 6,575 496 6,213 40 12 7 HG-6-85 Fed Reg only -107.86250 40.48583 8 T6N R93W 6,645 1,355 8 HG-5-85 Fed Reg only -107.85750 40.47083 17 T6N R93W 6,635 1,195 5,517 62 13 23 6 9 Y-17-HG 76-817 -107.85706 40.49042 8 T6N R93W 6,640 950 10 HG-5-85C Fed Reg only -107.85583 40.47139 17 T6N R93W 6,635 950 20 5 11 Y-14-HG 76-817 -107.85086 40.46514 17 T6N R93W 6,640 938 5,867 48 8 14 3 7 3 12 R-15-HG 85-37 -107.84934 40.48031 8 T6N R93W 6,620 1,520 8 3 

13 R-18-HG 85-43 -107.84255 40.45944 21 T6N R93W 6,715 1,420 5,413 52 12 23 4 9 3 14 R-1-HG 78-366 -107.82802 40.44422 27 T6N R93W 6,775 1,089 5,800 31 9 24 3 21 4 15 R-17-HG 85-43 -107.82688 40.47250 15 T6N R93W 6,290 1,500 4,829 49 12 58 14 9 4 16 R-2-HG 78-366 -107.82630 40.45163 22 T6N R93W 6,650 1,250 5,440 45 14 18 3 7 2 17 HG-1-81 85-37 -107.82494 40.48325 10 T6N R94W 6,371 2,300 4,156 45 10 77 11 11 4 18 Y-16-HG 76-817 -107.81797 40.45161 22 T6N R93W 6,680 1,000 44 11 13 4 19 Y-15-HG 76-817 -107.81781 40.47000 15 T6N R93W 6,120 800 14 5 20 R-3-HG 78-366 -107.81644 40.45992 22 T6N R93W 6,350 967 25 6 15 6 21 R-6-HG 78-366 -107.81225 40.44813 27 T6N R93W 6,615 1,184 28 5 20 4 22 R-5-HG 78-366 -107.80714 40.45433 23 T6N R93W 6,460 928 9 2 23 R-16-HG 85-37 -107.80467 40.46579 14 T6N R93W 6,320 1,947 4,476 60 19 64 15 17 6 24 R-7-HG 78-366 -107.79813 40.44477 26 T6N R93W 6,370 1,183 48 8 26 6 25 R-4-HG 78-366 -107.79553 40.46033 23 T6N R93W 6,410 1,066 11 4 26 R-8-HG 78-366 -107.78801 40.44167 25 T6N R93W 6,242 1,256 31 9 12 527 R-9-HG 78-366 -107.77263 40.44640 25 T6N R93W 6,438 1,106 12 328 R-12-HG 78-366 -107.77124 40.42660 31 T6N R92W 6,518 1,285 57 10 27 7 20 629 R-13-HG 78-366 -107.77117 40.43518 30 T6N R92W 6,445 915 20 8 17 330 HG-2-81 85-37 -107.76842 40.45783 19 T6N R92W 6,200 2,247 4,050 75 15 54 15 11 2 31 R-10-HG 78-366 -107.76233 40.44133 30 T6N R92W 6,420 1,102 13 332 R-11-HG 78-366 -107.76175 40.43034 31 T6N R92W 6,355 1,501 4,936 61 16 39 9 27 833 E-16-HG 78-229 -107.75253 40.42523 32 T6N R92W 6,320 1,380 4,964 66 11 27 8 21 634 E-5-RDB 78-229 -107.74986 40.39961 8 T5N R92W 6,100 440 5,71635 E-4-RDB 78-229 -107.74353 40.41148 5 T5N R92W 6,660 1,406 5,318 69 16 20 6 14 436 MC-1 85-43 -107.74225 40.39131 8 T5N R92W 6,760 1,002 5,875 97 17 33 437 MC-2 85-43 -107.72803 40.39286 9 T5N R92W 6,710 1,300 5,692 67 14 18 3 8 238 RB-3-81 85-37 -107.72769 40.45083 21 T6N R92W 6,195 2,319 14 4 13 5 39 E-24-MB 79-328 -107.72397 40.37421 21 T5N R92W 7,165 580 6,675 59 1340 E-2-RDB 78-229 -107.71812 40.41287 4 T5N R92W 6,290 1,415 32 6 19 541 MC-3 85-43 -107.71686 40.39172 9 T5N R92W 6,840 1,380 5,758 67 16 46 5 15 542 E-21-RDB 79-328 -107.70864 40.39967 10 T5N R92W 6,500 1,320 5,312 73 15 42 6 10 343 1USADOROUGH O&G -107.70770 40.58140 3 T7N R92W 6,767 4,810 2,06944 E-8-RDB 78-229 -107.70766 40.47614 15 T6N R92W 6,560 1,000 45 E-6-RDB 78-229 -107.69828 40.38735 15 T5N R92W 7,010 1,046 6,030 79 14 23 246 I.U.-1 85-43 -107.69814 40.40322 10 T5N R92W 6,410 1,359 5,142 80.1 18 33.5 4 16.5 447 E-11-RDB 78-229 -107.69759 40.45241 22 T6N R92W 6,380 860 17 548 ILES MTN #2 85-43 -107.69658 40.37919 14 T5N R92W 7,300 995 6,328 95 16 25 549 I.U.-3 85-43 -107.69614 40.37800 15 T5N R92W 7,300 900 6,507 55 1350 BRG-3 85-43 -107.68903 40.43839 26 T6N R92W 6,445 1,500 5,201 93 14 18 5 18 651 BRG-1 85-43 -107.68878 40.45983 23 T6N R92W 6,460 1,763 4,759 84 17 33 5 10 352 E-26-RDB 79-328 -107.68291 40.47312 14 T6N R92W 6,365 943 

A coal zone B coal zone C coal zone 
Surface Total Top of Trout

Map Point ID Source Longitude Latitude Section Township Range elevation depth Creek Sandstone Total Total Tota

no. (ft) (ft) elev. (ft) coal (ft) # beds coal (ft) # beds coal (

A coal zone B coal zone C co

53 E-13-RDB 78-229 -107.68043 40.44091 26 T6N R92W 6,720 961 13 4 21 54 E-22-RDB 79-328 -107.67847 40.37714 14 T5N R92W 7,410 1,120 6,488 82 15 24 355 BRG-2 85-43 -107.67445 40.45651 24 T6N R92W 6,370 1,810 4,788 74 17 33 5 13 56 E-25-MB 79-328 -107.67069 40.36721 24 T5N R92W 7,480 700 6,896 73 1157 E-12-RDB 78-229 -107.66910 40.44640 25 T6N R92W 6,610 1,400 11 3 11 58 RB-2-81C 85-37 -107.66906 40.44640 25 T6N R92W 6,600 1,480 9 2 13 59 RB-1-81 85-37 -107.66760 40.47453 13 T6N R92W 6,382 2,070 4,402 65 11 31 2 14 60 1GOVT O&G -107.64320 40.55990 18 T7N R91W 6,980 5,180 1,82461 CG-1 85-43 -107.62697 40.41352 5 T5N R91W 7,270 1,105 19 562 E-1-RDB 78-229 -107.62631 40.41989 5 T5N R91W 7,090 1,106 17 4 11 63 1 BILSING O&G -107.62611 40.49361 8 T6N R91W 6,338 1,730 4,64864 H-40-H 82-475 -107.60181 40.30272 22 T4N R91W 7,235 631 6,724 89 1965 H-21-P 77-118 -107.59682 40.29234 27 T4N R91W 7,895 400 7,62666 H-34-H 78-366 -107.58900 40.29585 27 T4N R91W 7,725 520 7,305 96 1267 C-1C-H 82-475 -107.58315 40.29916 23 T4N R91W 7,615 884 23 268 H-12-P 77-118 -107.58312 40.29945 23 T4N R91W 7,615 380 23 269 C-1A-H 82-475 -107.58296 40.29840 23 T4N R91W 7,615 875 7,05270 C-1-H 82-475 -107.58284 40.29922 23 T4N R91W 7,610 906 22 271 H-22-P 77-118 -107.57758 40.31530 14 T4N R91W 7,592 500 7,33372 H-14-P 77-118 -107.57603 40.31077 14 T4N R91W 7,695 280 15 273 CG-4 85-43 -107.57476 40.40440 11 T5N R91W 7,240 500 6,87774 CG-3 85-43 -107.57339 40.41067 2 T5N R91W 7,460 1,035 6,495 85 9 9 275 H-26-P 77-118 -107.56361 40.29630 24 T4N R91W 7,785 460 23 276 H-20-P 77-118 -107.56294 40.29247 25 T4N R91W 7,870 480 21 277 H-33-H 78-366 -107.56007 40.28749 25 T4N R91W 8,060 1,005 7,201 99 13 6 278 H-35-H 78-366 -107.55956 40.31138 13 T4N R91W 7,262 1,300 6,202 106 15 22 279 H-36-H 82-475 -107.55753 40.30741 24 T4N R91W 7,350 1,825 5,772 97 12 20 2 11 80 CG-6 85-43 -107.55637 40.39696 12 T5N R91W 7,610 800 7,41981 CG-5 85-43 -107.55509 40.40712 12 T5N R91W 7,680 895 6,865 66 11 5 282 H-32-H 78-366 -107.52975 40.27303 32 T4N R90W 8,135 631 7,666 94 1283 CG-7 85-43 -107.52518 40.39954 8 T5N R90W 7,565 920 7,09284 CG-8 85-43 -107.52413 40.40765 8 T5N R90W 7,565 1,000 6,661 76 17 8 285 CG-9 85-43 -107.50250 40.40642 9 T5N R90W 7,445 940 6,637 66 16 8 286 BM-37 78-365 -107.49822 40.42408 4 T5N R90W 7,320 980 12 1 9.5 87 BM-59 85-43 -107.49239 40.44783 28 T6N R90W 6,895 1,000 11 2 9 88 1-16 STATE O&G -107.49222 40.47889 16 T6N R90W 6,478 1,866 4,61889 BM-20 77-155 -107.49158 40.41308 4 T5N R90W 7,060 580 3 190 BM-19 77-155 -107.49039 40.40686 9 T5N R90W 6,970 569 6,419 61.8 1791 BM-36 78-365 -107.48806 40.42278 4 T5N R90W 7,480 1,000 10.5 2 7.5 92 BM-58 85-43 -107.48597 40.43906 33 T6N R90W 6,945 1,000 11 2 11 93 H-41-P 82-475 -107.48422 40.26056 3 T3N R90W 8,270 960 7,531 58 1294 H-31-P 78-366 -107.48239 40.25342 3 T3N R90W 8,442 950 7,967 61 895 BM-53 85-43 -107.48169 40.42914 34 T6N R90W 7,340 1,500 6.5 1 10 96 BM-50 85-43 -107.47725 40.41639 3 T5N R90W 7,640 715 5 1 6.5 97 BM-49 85-43 -107.47444 40.39992 10 T5N R90W 7,485 960 6,617 72 16 4 198 BM-17 77-155 -107.47303 40.40061 10 T5N R90W 7,480 580 2.5 199 BM-18 77-155 -107.47147 40.40933 10 T5N R90W 7,280 580 8.3 3

100 BM-54 85-43 -107.46847 40.43250 34 T6N R90W 7,330 1,040 9 3 7.5 101 BM-16 77-155 -107.46744 40.39828 11 T5N R90W 7,540 560 5 1102 BM-34 78-365 -107.46211 40.42967 35 T6N R90W 7,480 840 4 1 9 103 BM-39 78-365 -107.45942 40.40883 11 T5N R90W 7,760 760 5 2

104 BM-48 85-43 -107.45744 40.40547 11 T5N R90W 7,360 1,180 6,480 62.5 15 0 0
Surface Total Top of Trout

Map Point ID Source Longitude Latitude Section Township Range elevation depth Creek Sandstone Total Total Tota

no. (ft) (ft) elev. (ft) coal (ft) # beds coal (ft) # beds coal (

A coal zone B coal zone C co

105 BM-44 78-365 -107.45147 40.42875 35 T6N R90W 7,440 880 2.5 1 2 106 BM-31 78-365 -107.45089 40.42017 2 T5N R90W 7,680 820 3 1 7 107 BM-38 78-365 -107.44650 40.41336 1 T5N R90W 7,700 820 4 1 10 108 BM-33 78-365 -107.44519 40.42964 36 T6N R90W 7,320 640 5 109 BM-14 77-155 -107.44394 40.39856 12 T5N R90W 7,480 580 15.5 1110 BM-13 77-155 -107.43569 40.40967 1 T5N R90W 7,800 545 6.5 111 BM-30 78-365 -107.42600 40.42128 6 T5N R89W 7,150 885 13 1112 BM-29 78-365 -107.41775 40.42814 31 T6N R89W 6,960 600 3 1113 BM-22 77-155 -107.41431 40.38594 18 T5N R89W 7,925 580 7.5 1114 BM-12 77-155 -107.41247 40.41906 6 T5N R89W 7,160 580 12 1115 BM-10 77-155 -107.40933 40.40528 8 T5N R89W 7,830 440 10.5 116 1 LYONS O&G -107.40583 40.44194 29 T6N R89W 6,751 2,104 4,743117 BM-28 77-155 -107.40531 40.41992 5 T5N R89W 7,550 580 9.5 118 BM-46 85-43 -107.40144 40.39800 8 T5N R89W 7,640 1,180 6,740 61.5 11 5 1119 HAY COAL 22-4 O&G -107.40111 40.41917 4 T5N R89W 7,345 1,675 5,725 61 9 10 1 8 120 BM-45 85-43 -107.39858 40.40906 8 T5N R89W 7,300 1,005 6,406 66 14 6 1121 BM-23 77-155 -107.39803 40.38472 17 T5N R89W 7,850 580 6 1122 BM-06 77-155 -107.39772 40.40100 8 T5N R89W 7,520 581 10 1123 BM-40 78-365 -107.39667 40.39328 17 T5N R89W 7,740 1,040 6,763 60 13 3 1124 BM-24 78-365 -107.39458 40.37622 20 T5N R89W 7,830 720 9 1125 BM-03 77-155 -107.38966 40.42230 4 T5N R89W 6,950 580 4 1126 BM-25 77-155 -107.38683 40.39997 9 T5N R89W 7,830 500 9 127 BM-01 77-155 -107.38622 40.42806 33 T6N R89W 6,840 570 10 128 BM-26 77-155 -107.38478 40.40997 4 T5N R89W 7,520 580 6 129 BM-42 78-365 -107.38397 40.37522 21 T5N R89W 7,900 800 10 2 9 130 BM-27 77-155 -107.38272 40.41772 4 T5N R89W 7,370 580 8 131 BM-02 77-155 -107.37795 40.41149 4 T5N R89W 7,415 580 6 132 BM-43 78-365 -107.37525 40.40203 9 T5N R89W 7,300 560 4 133 HAY-8 78-365 -107.37382 40.37597 21 T5N R89W 7,770 780 10 134 HAYG-11 78-365 -107.37203 40.35797 27 T5N R89W 7,900 800 2 1135 HAY-9 78-365 -107.36511 40.38699 15 T5N R89W 7,400 800 7 136 HAY-4 77-155 -107.36424 40.39999 10 T5N R89W 7,660 580 10 137 HAY-3 77-155 -107.35735 40.39557 10 T5N R89W 6,900 523138 HAYG-14 85-43 -107.35329 40.34792 35 T5N R89W 7,805 600 7,278 59 15139 HAYG-10 78-365 -107.35095 40.36745 23 T5N R89W 7,320 800 3 1140 HAYG-4 77-155 -107.34315 40.35119 26 T5N R89W 7,660 560 2 1141 HAYG-6 77-155 -107.34277 40.36319 26 T5N R89W 7,960 578 6 142 HAYG-12 78-365 -107.34264 40.34849 35 T5N R89W 7,320 710 6,991143 HAY-2 77-155 -107.34211 40.38684 14 T5N R89W 7,300 580 12 144 HAY-5 77-155 -107.34148 40.39677 11 T5N R89W 6,850 578 9 145 HAYG-3 77-155 -107.33135 40.35369 25 T5N R89W 7,270 560 3 1146 HAY-11 85-43 -107.32789 40.39437 13 T5N R89W 6,890 760 2 147 HAY-7 78-365 -107.32629 40.38649 13 T5N R89W 7,000 753 2 148 HAYG-15A 85-43 -107.32275 40.35119 25 T5N R89W 7,920 1,460 0 0 0 149 HAY-6A 77-155 -107.31944 40.39465 13 T5N R89W 6,820 551150 HAYG-9 78-365 -107.31656 40.36300 25 T5N R89W 7,700 770 0 151 BRESH 14-30 O&G -107.31306 40.44278 30 T6N R88W 6,514 2,638 3,944 80 11 152 Y-25-H 76-817 -107.28722 40.39922 8 T6N R88W 6,800 619 153 Y-22-H 76-817 -107.26739 40.43378 33 T6N R88W 7,528 540 

154 DCU 0-28-6-88-N O&G -107.25750 40.44167 28 T6N R88W 6,517 2,152 4,443 42 10 155 DCU 12-2 HD O&G -107.23750 40.41833 2 T5N R88W 7,443 1,060 6,443

156 FCU 3-2 O&G -107.22942 40.42681 2 T5N R88W 7,225 930 6,375 30 6
Surface Total Top of Trout

Map Point ID Source Longitude Latitude Section Township Range elevation depth Creek Sandstone Total Total Tota

no. (ft) (ft) elev. (ft) coal (ft) # beds coal (ft) # beds coal (

A coal zone B coal zone C co

157 GRACE 1-27 O&G -107.13222 40.45083 27 T6N R87W 6,819 678 6,181158 RB-22 78-1048 -107.12411 40.30019 23 T4N R87W 7,930 315 7,643159 JOSE ROCHE 23-5 O&G -107.11667 40.37889 23 T5N R87W 6,863 1,475 5,460160 RB-20 78-1048 -107.10644 40.29750 23 T4N R87W 8,040 255 7,813161 RB-19 78-1048 -107.09849 40.30148 19 T4N R86W 7,920 215 7,723162 FCU 6-36 O&G -107.09806 40.34056 3 T5N R87W 7,050 1,420 5,755163 RB-18 78-1048 -107.08832 40.30811 19 T4N R86W 7,746 315 7,456164 RB-17 78-1048 -107.05394 40.32948 9 T4N R86W 7,620 335 7,297165 M-3 78-365 -107.03078 40.43356 34 T6N R86W 6,860 1,000 6,151 21 4166 M-4 78-365 -107.02483 40.42433 3 T5N R86W 6,670 1,005 5,906 30 4167 RB-14 78-365 -107.01531 40.35067 34 T5N R86W 7,140 1,230 5,917 23 6168 M-5 78-365 -107.01433 40.42028 3 T5N R86W 6,640 807 6,290 21 5169 RB-12 78-365 -107.00822 40.32658 11 T4N R86W 7,540 1,185 6,471 23 5170 RB-15 78-365 -107.00494 40.34450 35 T5N R86W 7,560 1,250 6,394 25 6171 RB-13 78-365 -107.00089 40.33346 11 T4N R86W 7,460 1,130 6,399 21 5172 OC-1 78-365 -106.99892 40.32492 14 T4N R86W 7,280 775 6,624 26 5173 OC-2 78-365 -106.98694 40.34314 36 T5N R86W 7,070 776 6,480 20 6174 OC-3 78-365 -106.98517 40.35303 36 T5N R86W 7,070 717 6,476 27 9175 CC-1 78-365 -106.96639 40.40506 7 T5N R85W 6,720 700 6,356
Appendix 3—Estimated Remaining Coal Resources in the A Coal Zone,

Williams Fork Formation, Yampa Coal Field

Appendix 3a. Estimated coal resources (in millions of short tons) in beds 1.2 ft thick or greater, by county, 

as expressed in reliability and maximum overburden categories. Resources in net-coal thickness categories 

are not listed in Appendix 3a, nor is a figure of coal-thickness categories provided because net coal in the A 

zone is everywhere greater than 14 ft. Does not include mined-out areas or areas where A-zone coal is 

included in an active coal lease. Totals might not equal the sum of their components in any particular 

column because of independent rounding. 

 

 Maximum overburden (ft) 

County Reliability 0-500 500-1,000 1,000-2,000 2,000-3,000 >3,000 Total 

Moffat Identified 2,500 2,100 6,300 2,500 610 14,000 

 Hypothetical 0 12 1,100 2,700 11,000 15,000 

Moffat Total 2,500 2,100 7,400 5,200 11,000 29,000 

 

Routt Identified 900 1,100 3,100 2,000 410 7,400 

 Hypothetical 370 320 1,200 1,400 2,900 6,100 

Routt Total 1,300 1,400 4,300 3,300 3,300 14,000 

Total 3,800 3,500 12,000 8,500 15,000 42,000 

 

Appendix 3b. Estimated coal resources in maximum overburden categories by surface ownership. 

Non-Federal surface includes State and private. 

 

 Maximum overburden (ft) 

Surface owner 0-500 500-1,000 1,000-2,000 2,000-3,000 >3,000 Total 

Federal 800 700 670 350 720 3,200 

Non-Federal 3,000 2,800 11,000 8,200 14,000 39,000 

 

Total 3,800 3,500 12,000 8,500 15,000 42,000 

 

Appendix 3c. Estimated coal resources in maximum overburden categories by coal ownership. 

Non-Federal coal includes State and private. 

 

 Maximum overburden (ft) 

Coal owner 0-500 500-1,000 1,000-2,000 2,000-3,000 >3,000 Total 

Federal 3,300 2,700 6,700 5,400 10,000 28,000 

Non-Federal 470 820 5,000 3,100 4,600 14,000 

 

Total 3,800 3,500 12,000 8,500 15,000 42,000 

 

P52 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Appendix 3d. Estimated coal resources in maximum overburden categories by 7.5’ quadrangle. 

 

 Maximum overburden (ft) 

7.5’ quadrangle 0-500 500-1,000 1,000-2,000 2,000-3,000 >3,000 Total 

Breeze Mountain 180 470 1,700 1,600 0.25 3,900 

Castor Gulch 250 200 2,200 150 0 2,800 

Cow Creek 78 41 14 0 0 130 

Craig 0 0 300 740 2,200 3,200 

Dunckley 170 62 59 0 0 290 

Hamilton 950 530 260 0 0 1,700 

Hayden 0 73 1,300 1,800 890 4,100 

Hayden Gulch 220 410 550 0 0 1,200 

Hooker Mountain 13 9 99 140 0 260 

Horse Gulch 340 260 900 750 130 2,400 

Juniper Hot Springs 84 59 0 0 0 140 

Lay 0 45 180 140 73 440 

Lay SE 0 0.91 310 970 3,100 4,400 

Milner 220 110 460 0 0 790 

Monument Butte 170 40 0 0 0 210 

Mount Harris 120 130 780 390 0 1,400 

Oak Creek 200 59 2.6 0 0 260 

Pagoda 450 120 0 0 0 570 

Pine Ridge 0 0 0 190 3,200 3,400 

Ralph White Lake 0 0 11 720 2,900 3,600 

Rattlesnake Butte 78 180 320 0 0 580 

Rock Spring Gulch 0 0 0 21 2,000 2,000 

Round Bottom 250 720 2,200 1,000 140 4,300 

Wolf Mountain 24 0 0 0 0 24 

 

Total 3,800 3,500 12,000 8,500 15,000 42,000 

 

Geology and Resource Assessment of the Middle and Upper Coal Groups, Yampa Coal Field, Northwestern Colorado P53
Appendix 3e. Estimated coal resources in overburden categories by township. 

 

 Maximum overburden (ft) 

Township 0-500 500-1,000 1,000-2,000 2,000-3,000 >3,000 Total 

3N 90W 110 48 0 0 0 160 

4N 85W 53 0 0 0 0 53 

4N 86W 120 90 26 0 0 230 

4N 87W 91 47 53 0 0 190 

4N 88W 110 110 0.13 0 0 220 

4N 90W 810 330 72 0 0 1,200 

4N 91W 380 220 190 0 0 780 

5N 85W 79 1.9 0 0 0 81 

5N 86W 100 180 410 0 0 700 

5N 87W 100 130 610 0 0 840 

5N 88W 140 220 950 52 0 1,400 

5N 89W 250 530 1,200 98 0 2,100 

5N 90W 210 280 390 0 0 890 

5N 91W 270 140 87 0 0 510 

5N 92W 390 660 450 0 0 1,500 

5N 93W 91 0.51 0 0 0 91 

6N 86W 100 43 33 0 0 180 

6N 87W 120 48 380 75 0 620 

6N 88W 0.85 11 250 1,100 620 2,000 

6N 89W 0 0 330 1,900 770 3,000 

6N 90W 0 0 1,500 1,000 0 2,500 

6N 91W 1.4 62 2,100 450 8.6 2,600 

6N 92W 39 74 1,400 1,200 410 3,100 

6N 93W 200 280 790 580 110 2,000 

6N 94W 26 0 0 0 0 26 

7N 89W 0 0 0 29 2,900 2,900 

7N 90W 0 0 0.2 550 2,200 2,800 

7N 91W 0 0 4 380 2,200 2,600 

7N 92W 0 0 0 13 3,000 3,000 

7N 93W 0 18 420 1,000 2,400 3,900 

Total 3,800 3,500 12,000 8,500 15,000 42,000 

 

P54 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Appendix 4a. Estimated coal resources (in millions of short tons) in beds 1.2 ft thick or greater, by county, as expressed in reliability, net-coal thimaximum overburden categories. Does not include mined-out areas or areas where B-zone coal is included in an active coal lease. Totals mighsum of their components in any particular column because of independent rounding. 0-500 ft maximum overburden 0-500 500-1,000 ft maximum overburden 

Net-coal thickness category Total Net-coal thickness category 

County Reliability 1.2-2.3 2.3-3.5 3.5-7.0 7.0-14.0 >14.0 1.2-2.3 2.3-3.5 3.5-7.0 7.0-14.0 >14

Moffat Identified 0.54 2.1 9 57 390 450 0.25 2.1 14 210 740 

Hypothetical 0 0 0 0 0 0 0 0 0 16 1

Moffat Total 0.54 2.1 9 57 390 450 0.25 2.1 14 220 740 Routt Identified 2.5 4.3 17 27 0.39 51 3.5 7.2 19 29 10 Routt Total 2.5 4.3 17 27 0.39 51 3.5 7.2 19 29 10 Total 3.1 6.5 26 84 390 510 3.8 9.3 33 250 750 

1,000-2,000 ft maximum overburden 1,000-2,000 2,000-3,000 ft maximum overburden 

Net-coal thickness category Total Net-coal thickness category 

County Reliability 1.2-2.3 2.3-3.5 3.5-7.0 7.0-14.0 >14.0 1.2-2.3 2.3-3.5 3.5-7.0 7.0-14.0 >14

Moffat Identified 5.9 7.6 27 83 1,800 2,000 0 0 0 0 1,500 

Hypothetical 2.2 2.8 14 50 340 410 1.8 2.8 13 47 1,500 

Moffat Total 8.1 10 41 130 2,200 2,400 1.8 2.8 13 47 3,000 Routt Identified 0.9 0.77 1.8 1.4 0 4.8 0 0 0 0 0 Routt Total 0.9 0.77 1.8 1.4 0 4.8 0 0 0 0 0 Total 9 11 43 130 2,200 2,400 1.8 2.8 13 47 3,000 

 >3,000 ft maximum overburden >3,000 Total  Net-coal thickness category Total 

County Reliability 1.2-2.3 2.3-3.5 3.5-7.0 7.0-14.0 >14.0 

Moffat Identified 0 0 0 0 79 79 4,900  Hypothetical 3.2 4.8 22 62 5,600 5,700 7,700 Moffat Total 3.2 4.8 22 62 5,700 5,800 13,000 Routt Identified 0 0 0 0 0 0 130 Routt Total 0 0 0 0 0 0 130 Total 3.2 4.8 22 62 5,700 5,800 13,000 
Appendix 4b. Estimated coal resources in maximum overburden categories by surface ownership. 

Non-Federal surface includes State and private. 

 

 Maximum overburden (ft) 

Surface owner 0-500 500-1,000 1,000-2,000 2,000-3,000 >3,000 Total 

Federal 190 200 200 260 410 1,300 

Non-Federal 320 850 2,200 2,800 5,400 11,000 

 

Total 510 1,000 2,400 3,000 5,800 13,000 

Appendix 4c. Estimated coal resources in maximum overburden categories by coal ownership. 

Non-Federal coal includes State and private. 

 

 Maximum overburden (ft) 

Coal owner 0-500 500-1,000 1,000-2,000 2,000-3,000 >3,000 Total 

Federal 410 660 1,800 2,800 4,000 9,700 

Non-Federal 91 390 590 260 1,700 3,100 

 

Total 510 1,000 2,400 3,000 5,800 13,000 

Appendix 4d. Estimated coal resources in maximum overburden categories by 7.5’ quadrangle. 

 

 Maximum overburden (ft) 

7.5’ Quadrangle 0-500 500-1,000 1,000-2,000 2,000-3,000 >3,000 Total 

Breeze Mountain 53 110 79 0 0 250 

Castor Gulch 18 260 260 0 0 540 

Craig 0 5.8 210 300 930 1,400 

Hamilton 86 15 0 0 0 100 

Hayden 4.6 13 0.02 0 0 18 

Hayden Gulch 7 6.6 0 0 0 14 

Horse Gulch 110 270 740 500 2.1 1,600 

Juniper Hot Springs 15 0 0 0 0 15 

Lay 12 37 87 99 0 230 

Lay SE 0.35 29 370 1,300 2,000 3,700 

Monument Butte 5.8 0 0 0 0 5.8 

Pagoda 7.1 0.36 0 0 0 7.4 

Pine Ridge 0 0 6.2 380 2,800 3,200 

Ralph White Lake 0 0 14 33 91 140 

Round Bottom 190 290 610 430 0 1,500 

 

Total 510 1,000 2,400 3,000 5,800 13,000 

P56 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Appendix 4e. Estimated coal resources in maximum overburden categories 

by township. 

 

 Maximum overburden (ft) 

Township 0-500 500-1,000 1,000-2,000 2,000-3,000 >3,000 Total 

4N 90W 21 1.6 0 0 0 22 

4N 91W 65 13 0 0 0 79 

5N 89W 51 66 1.4 0 0 120 

5N 90W 30 35 1.7 0 0 66 

5N 91W 13 11 0 0 0 24 

5N 92W 190 180 2.3 0 0 380 

5N 93W 0.35 0 0 0 0 0.35 

6N 89W 0 3 3.4 0 0 6.4 

6N 90W 0 130 120 0 0 250 

6N 91W 9.6 180 570 93 0 850 

6N 92W 11 130 510 750 45 1,500 

6N 93W 110 240 680 450 7.1 1,500 

7N 89W 0 0 0 0 0.06 0.06 

7N 90W 0 0 34 110 250 390 

7N 91W 0 0 54 270 1,400 1,700 

7N 92W 0 0 0 110 2,800 2,900 

7N 93W 5.2 55 400 1,200 1,300 3,000 

 

Total 510 1,000 2,400 3,000 5,800 13,000 

 

Geology and Resource Assessment of the Middle and Upper Coal Groups, Yampa Coal Field, Northwestern Colorado P57
Appendix 5a. Estimated coal resources (in millions of short tons) in beds 1.2 ft thick or greater, by county as expressed in reliability, ne

thickness, and maximum overburden categories. Does not include mined-out areas or areas where C-zone coal is included in an active lease. Totals might not equal the sum of their components in any particular column because of independent rounding. 0-500 ft maximum overburden 0-500 500-1,000 ft maximum overburden 

Net-coal thickness category Total Net-coal thickness category 

County Reliability 1.2-2.3 2.3-3.5 3.5-7.0 7.0-14.0 >14.0 1.2-2.3 2.3-3.5 3.5-7.0 7.0-14.0 >14.0 Moffat Identified 1.1 1.9 29 200 180 410 1.7 2.5 130 300 170 

Hypothetical 0 0 0 0.87 0 0.87 0.26 0 26 7.6 0 

Moffat Total 1.1 1.9 29 210 180 410 2 2.5 150 310 170 Routt Identified 1 1.3 22 130 0 150 1.1 1.3 32 35 0 

Hypothetical 0 0 0 0 0 0 0 0 2.1 0 0 

Routt Total 1 1.3 22 130 0 150 1.1 1.3 34 35 0 Total 2.1 3.3 52 330 180 570 3.1 3.8 190 350 170 

1,000-2,000 ft maximum overburden 1,000-2,000 2,000-3,000 ft maximum overburden 2,000-3,00

Net-coal thickness category Total Net-coal thickness category Total County Reliability 1.2-2.3 2.3-3.5 3.5-7.0 7.0-14.0 >14.0 1.2-2.3 2.3-3.5 3.5-7.0 7.0-14.0 Moffat Identified 0.08 1.2 47 400 24 470 0 0 3.3 110 120 Hypothetical 5 4.4 110 57 0 170 9 11 200 350 570 

Moffat Total 5 5.6 150 460 24 640 9 11 200 470 690 Routt Identified 1 1.9 45 13 0 61 0 0 0 0 0  Hypothetical 6.4 16 69 0 0 91 8.8 21 65 0 95 Routt Total 7.4 18 110 13 0 150 8.8 21 65 0 95 Total 12 23 270 470 24 800 18 32 270 470 780 

 >3,000 ft maximum overburden >3,000 Total  Net-coal thickness category Total 

County Reliability 1.2-2.3 2.3-3.5 3.5-7.0 7.0-14.0 

Moffat Identified 0 0 0 0 0 1,600  Hypothetical 10 14 240 550 810 1,600 Moffat Total 10 14 240 550 810 3,200 Routt Identified 0 0 0 0 0 280  Hypothetical 0 2 67 0 70 260 Routt Total 0 2 67 0 70 540 Total 10 16 300 550 880 3,700 
Appendix 5b. Estimated coal resources in maximum overburden categories by surface 

ownership. Non-Federal surface includes State and private. 

 

 Maximum overburden (ft) 

Surface owner 0-500 500-1,000 1,000-2,000 2,000-3,000 >3,000 Total 

Federal 130 39 44 32 51 300 

Non-Federal 430 670 760 750 830 3,400 

Total 570 710 800 780 880 3,700 

Appendix 5c. Estimated coal resources in maximum overburden categories by coal 

ownership. Non-Federal coal includes State and private. 

 

 Maximum overburden (ft) 

Coal owner 0-500 500-1,000 1,000-2,000 2,000-3,000 >3,000 Total 

Federal 430 460 600 630 560 2,700 

Non-Federal 130 250 200 160 300 1,000 

Total 570 710 800 780 880 3,700 

Appendix 5d. Estimated coal resources in maximum overburden categories by 7.5’ quadrangle. 

 

 Maximum overburden (ft) 

7.5’ quadrangle 0-500 500-1,000 1,000-2,000 2,000-3,000 >3,000 Total 

Breeze Mountain 120 130 100 0 0 360 

Castor Gulch 49 200 19 0 0 270 

Craig 0 34 110 130 240 510 

Hamilton 20 0 0 0 0 20 

Hayden 56 31 76 14 0 180 

Hayden Gulch 21 0 0 0 0 21 

Horse Gulch 120 100 150 19 0 390 

Juniper Hot Springs 0.66 0 0 0 0 0.66 

Lay 0.42 0 0 0 0 0.42 

Lay SE 0.89 5.7 46 200 67 320 

Pagoda 2.6 0 0 0 0 2.6 

Pine Ridge 0 0 27 210 370 600 

Ralph White Lake 0 1.7 74 140 130 350 

Rock Spring Gulch 0 0 0.82 51 73 120 

Round Bottom 180 200 200 25 0 600 

 

Total 570 710 800 780 880 3,700 

Geology and Resource Assessment of the Middle and Upper Coal Groups, Yampa Coal Field, Northwestern Colorado P59
Appendix 5e. Estimated coal resources in maximum overburden categories by township. 

 

 Maximum overburden (ft) 

Township 0-500 500-1,000 1,000-2,000 2,000-3,000 >3,000 Total 

4N 90W 3.6 0 0 0 0 3.6 

4N 91W 16 0 0 0 0 16 

5N 88W 0 0.2 0.24 0 0 0.44 

5N 89W 150 29 1.3 0 0 180 

5N 90W 42 11 0 0 0 54 

5N 91W 9 0 0 0 0 9 

5N 92W 100 19 0 0 0 120 

6N 88W 0 0 5.8 12 0 18 

6N 89W 0.96 43 140 22 0 210 

6N 90W 27 140 71 0 0 240 

6N 91W 35 210 100 4.9 0 360 

6N 92W 87 170 210 71 0 540 

6N 93W 93 75 120 19 0 300 

7N 89W 0 0 5.1 99 120 220 

7N 90W 0 0 62 120 140 320 

7N 91W 0 0 53 110 290 460 

7N 92W 0 0 0 190 290 480 

7N 93W 0.27 3.8 32 130 35 200 

 

Total 570 710 800 780 880 3,700 

P60 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Appendix 6—Estimated Remaining Coal Resources in the D Coal Zone,

Williams Fork Formation, Yampa Coal Field

Appendix 6a. Estimated coal resources (in millions of short tons) in beds 1.2 ft thick or greater, by county as 

expressed in reliability, net-coal coal thickness, and maximum overburden categories. Does not include mined-out 

areas or areas where D-zone coal is included in an active coal lease. Totals might not equal the sum of their 

components in any particular column because of independent rounding. 

 

 0-500 ft maximum overburden 0-500 500-1,000 ft maximum overburden 500-1,000 

 Net-coal thickness category Total Net-coal thickness category Total 

County Reliability 3.5-7.0 7.0-14.0 >14.0 3.5-7.0 7.0-14.0 >14.0 

Moffat Identified 4.5 21 1,900 1,900 0 0 1,900 1,900 

 Hypothetical 0 0 33 33 0 0 690 690 

Moffat Total 4.5 21 1,900 2,000 0 0 2,600 2,600 

Routt Identified 12 5.4 450 460 17 6.6 320 350 

 Hypothetical 1.1 0 92 93 7 0 47 54 

Routt Total 13 5.4 540 560 24 6.6 370 400 

Total 18 26 2,500 2,500 24 6.6 2,900 3,000 

 

 1,000-2,000 ft maximum overburden 1,000-2,000 2,000-3,000 ft maximum overburden 2,000-3,000 

 Net-coal thickness category Total Net-coal thickness category Total 

County Reliability 3.5-7.0 7.0-14.0 >14.0 7.0-14.0 >14.0 

Moffat Identified 0 0 1,500 1,500 0 400 400 

 Hypothetical 0 0 1,600 1,600 0 3,500 3,500 

Moffat Total 0 0 3,100 3,100 0 3,900 3,900 

 

Routt Identified 20 50 280 350 0 0 0 

 Hypothetical 34 45 500 580 7.6 620 620 

Routt Total 53 94 780 930 7.6 620 620 

Total 53 94 3,900 4,000 7.6 4,500 4,500 

 

 

 >3,000 ft maximum overburden >3000 

 Net-coal thickness category Total Total 

County Reliability >14.0 

Moffat Identified 0 0 5,700 

 Hypothetical 3,400 3,400 9,100 

Moffat Total 3,400 3,400 15,000 

 

Routt Identified 0 0 1,200 

 Hypothetical 150 150 1,500 

Routt Total 150 150 2,700 

 

Total 3,500 3,500 17,000 

Geology and Resource Assessment of the Middle and Upper Coal Groups, Yampa Coal Field, Northwestern Colorado P61
Appendix 6b. Estimated coal resources in maximum overburden categories by surface ownership. 

Non-Federal surface includes State and private. 

 

 Maximum overburden (ft) 

Surface owner 0-500 500-1,000 1,000-2,000 2,000-3,000 >3,000 Total 

 

Federal 190 88 210 190 250 930 

Non-Federal 2,300 2,900 3,800 4,300 3,300 17,000 

Total 2,500 3,000 4,000 4,500 3,500 17,000 

Appendix 6c. Estimated coal resources in maximum overburden categories by coal ownership. 

Non-Federal coal includes State and private. 

 

 Maximum overburden (ft) 

Coal Owner 0-500 500-1,000 1,000-2,000 2,000-3,000 >3,000 Total 

Federal 1,500 1,700 2,800 3,500 2,300 12,000 

Non-Federal 1,000 1,300 1,200 960 1,200 5,700 

Total 2,500 3,000 4,000 4,500 3,500 17,000 

Appendix 6d. Estimated coal resources in maximum overburden categories by 7.5’ quadrangle. 

 

 Maximum overburden (ft) 

7.5’ quadrangle 0-500 500-1,000 1,000-2,000 2,000-3,000 >3,000 Total 

Breeze Mountain 410 780 310 0 0 1,500 

Castor Gulch 880 580 0 0 0 1,500 

Craig 21 310 610 690 1,000 2,700 

Hamilton 19 0 0 0 0 19 

Hayden 310 190 480 0 0 980 

Hayden Gulch 110 0 0 0 0 110 

Hooker Mountain 0 2 11 0 0 13 

Horse Gulch 370 290 520 26 0 1,200 

Lay 49 34 67 33 0 180 

Lay SE 33 120 640 1,300 340 2,400 

Mount Harris 12 19 22 0 0 53 

Pagoda 0.25 0 0 0 0 0.25 

Pine Ridge 0 0 150 960 1,400 2,500 

Ralph White Lake 0 44 610 940 630 2,200 

Rock Spring Gulch 0 0 42 510 160 710 

Round Bottom 310 570 530 23 0 1,400 

 

Total 2,500 3,000 4,000 4,500 3,500 17,000 

P62 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Appendix 6e. Estimated coal resources in maximum overburden categories by township. 

 

 Maximum overburden (ft) 

Township 0-500 500-1,000 1,000-2,000 2,000-3,000 >3,000 Total 

4N 90W 0.02 0 0 0 0 0.02 

4N 91W 19 0 0 0 0 19 

5N 88W 240 36 0 0 0 270 

5N 89W 280 73 0 0 0 350 

5N 90W 140 0 0 0 0 140 

5N 91W 7.1 0 0 0 0 7.1 

5N 92W 73 5.3 0 0 0 78 

6N 88W 20 53 230 25 0 330 

6N 89W 23 240 620 50 0 930 

6N 90W 540 890 250 0 0 1,700 

6N 91W 550 850 190 4.6 0 1,600 

6N 92W 220 370 700 150 0 1,500 

6N 93W 340 260 410 28 0 1,000 

7N 89W 0 0 81 830 400 1,300 

7N 90W 0 14 550 830 640 2,000 

7N 91W 0 28 330 540 1,200 2,100 

7N 92W 0 0 13 1,000 1,100 2,100 

7N 93W 67 140 620 1,000 210 2,100 

8N 90W 0 0 0 0 0.14 0.14 

 

Total 2,500 3,000 4,000 4,500 3,500 17,000 

Geology and Resource Assessment of the Middle and Upper Coal Groups, Yampa Coal Field, Northwestern Colorado P63
Appendix 7—ArcView Project for the 

Yampa Coal Field, Northwestern Colorado

The digital fi les used for the coal resource assessment of the Yampa coal fi eld are presented as views in the ArcView 

project.

The ArcView project and the digital fi les are stored on both discs of this CD-ROM set—Appendix 7 of chapter P resides 

on both discs. Persons who do not have ArcView 3.1 may query the data by means of the ArcView Data Publisher on disc 1. 

Persons who do have ArcView 3.1 may utilize the full functionality of the software by accessing the data that reside on disc 2.

An explanation of the ArcView project and data library—and how to get started using the software—is given by Biewick and 

Mercier (chap. D, this CD-ROM). Metadata for all digital fi les are also accessible through the ArcView project.

Appendix 8—Stratigraphic Database for the 

Yampa Coal Field, Northwestern Colorado

Appendix 8 contains the database used to asses coal resources in the middle and upper coal groups in the Yampa coal 

fi eld. The location, lithologic, and stratigraphic data are available in ASCII format, DBF, and Excel spreadsheet fi les on disc 

2 of this CD-ROM.

P64 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Click on image below to bring up high-resolution image of plate 1.

Plate 1. Subsurface correlations of coal and related rocks in the middle and upper coal groups of the Upper Cretaceous Williams Fork 

Formation in the Yampa coal fi eld, northwestern Colorado.

National Coal

Resource

Assessment

Click here to return to Disc 1 

Volume Table of Contents

Geology and Resource Assessment of the Middle and Upper Coal Groups, Yampa Coal Field, Northwestern Colorado P65