Chapter M

Assessment of the Distribution and Resources

of Coal in the Fairfield Group of the 

Williams Fork Formation,

Danforth Hills Coal Field, Northwest Colorado

By M.E. Brownfield,1 L.N.R. Roberts,1 E.A. Johnson,1 and T.J. Mercier2

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

U.S. Department of the Interior

U.S. Geological Survey

National Coal

Resource

Assessment

Click here to return to Disc 1 

Volume Table of Contents

Chapter M 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
Contents

Abstract.......................................................................................................................................................M1

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

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

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

Previous Geologic Studies and Mining Activity ............................................................................. 4

Methods ................................................................................................................................................ 6

Geologic Maps ..................................................................................................................................... 6

Geographical Boundaries .................................................................................................................. 6

Geophysical Logs................................................................................................................................. 6

Acknowledgments............................................................................................................................. 10

Geologic Setting.......................................................................................................................................... 10

Stratigraphy of the Cretaceous and Tertiary Strata of the Danforth Hills Coal Field ............. 10

Structure ............................................................................................................................................. 11

Coal Geology of the Danforth Hills Coal Field ........................................................................................ 11

Stratigraphy ........................................................................................................................................ 11

Coal Distribution in the Fairfield Coal Group ................................................................................. 12

Coal Quality......................................................................................................................................... 13

Methodology................................................................................................................................................ 35

Coal Resources ........................................................................................................................................... 52

References Cited ........................................................................................................................................ 52

Appendix 1—Digital Files for Coal Exploration Drill Holes in the Danforth Hills Coal Field, 

Northwest Colorado, for which Data are Publicly Available

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

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

Appendix 2—ArcView Project for the Geologic Assessment of Coal in the Fairfield Coal Group, 

Williams Fork Formation, Danforth Hills Coal Field, Northwest Colorado

[The digital fi les used for the coal resource assessment of the Fairfi eld coal group 

of the Williams Fork Formation, Danforth Hills coal fi eld, northwest Colorado, 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 2 of chapter M 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 

them—is given by Biewick and Mercier (chap. D, this CD-ROM). Metadata for all digital 

fi les are also accessible through the ArcView project]
Plate

 1. Assessment of the distribution and resources of coal in the Fairfield 

coal group of the Williams Fork Formation Danforth Hills coal field, 

northwest Colorado.................................................................................................................M54

 Figure A. Generalized geologic map of the Danforth Hills coal field

 Figure B. Index map showing location of public drill holes in the 

Danforth Hills coal field, Colorado

 Figure C. Coal correlation in the Fairfield coal group, Danforth Hills 

coal field, Colorado

Figures

 1. Location map of the Danforth Hills coal field........................................................................M2

 2. Generalized geologic map of northwest Colorado ................................................................. 3

 3. Generalized regional cross section for part of the Upper Cretaceous and 

Tertiary rocks in the Lower White River, Danforth Hills, and Yampa 

coal fields, Colorado..................................................................................................................... 4

 4. Generalized stratigraphic column for a portion of the Upper Cretaceous 

rocks for the Danforth Hills coal field ....................................................................................... 5

 5. Index map showing location of 7.5’ quadrangles in the Danforth Hills coal field, 

Colorado ......................................................................................................................................... 7

 6. Map showing total net-coal thickness for the FGA coal zone............................................ 14

 7. Map showing total net-coal thickness for the FGB coal zone............................................ 15

 8. Map showing total net-coal thickness for the FGC coal zone ............................................ 16

 9. Map showing total net-coal thickness for the FGD coal zone............................................ 17

 10. Map showing total net-coal thickness for the FGE coal zone ............................................ 18

 11. Map showing total net-coal thickness for the FGF coal zone............................................. 19

 12. Map showing total net-coal thickness for the FGG coal zone............................................ 20

 13. Map showing overburden thickness for the FGA coal zone ............................................... 21

 14. Map showing overburden thickness for the FGB coal zone ............................................... 22

 15. Map showing overburden thickness for the FGC coal zone ............................................... 23

 16. Map showing overburden thickness for the FGD coal zone ............................................... 24

 17. Map showing overburden thickness for the FGE coal zone................................................ 25

 18. Map showing overburden thickness for the FGF coal zone................................................ 26

 19. Map showing overburden thickness for the FGG coal zone ............................................... 27

 20. Map showing coal-thickness categories for the FGA coal zone ....................................... 28

 21. Map showing coal-thickness categories for the FGB coal zone ....................................... 29

 22. Map showing coal-thickness categories for the FGC coal zone........................................ 30

 23. Map showing coal-thickness categories for the FGD coal zone ....................................... 31

 24. Map showing coal-thickness categories for the FGE coal zone........................................ 32
 25. Map showing coal-thickness categories for the FGF coal zone ........................................ 33

 26. Map showing coal-thickness categories for the FGG coal zone ....................................... 34

Tables

 1. Locations of publically available coal-exploration holes drilled in the 

Danforth Hills coal field, Colorado..........................................................................................M8

 2. Summary of the Fairfield coal zones of the Williams Fork................................................... 13

 3. Coal quality summary for coal collected from the Danforth Hills 

coal field, Colorado..................................................................................................................... 35

 4. Summary of ash content and 36 elements in coal from the Danforth Hills 

coal field, Colorado..................................................................................................................... 36

 5. Identified and hypothetical coal resources for the FGA zone of the 

Fairfield Group, Williams Fork Formation, Danforth coal field ............................................ 37

 6. Identified and hypothetical coal resources for the FGA zone of the 

Fairfield Group, Williams Fork Formation, Danforth Hills coal field by 

county, reliability, overburden, and coal thickness .............................................................. 38

 7. Identified and hypothetical coal resources for the FGB zone of the 

Fairfield Group, Williams Fork Formation, Danforth coal field by 

quadrangle, township, and ownership ................................................................................... 39

 8. Identified and hypothetical coal resources for the FGB zone of the 

Fairfield Group, Williams Fork Formation, Danforth Hills coal field by 

county, reliability, overburden, and coal-thickness.............................................................. 40

 9. Identified and hypothetical coal resources for the FGC zone of the 

Fairfield Group, Williams Fork Formation, Danforth coal field by 

quadrangle, township, and ownership ................................................................................... 41

 10. Identified and hypothetical coal resources for the FGC of the 

Fairfield Group, Williams Fork Formation, Danforth Hills coal field by 

county, reliability, overburden, and coal-thickness.............................................................. 42

 11. Identified and hypothetical coal resources for the FGD zone of the 

Fairfield Group, Williams Fork Formation, Danforth coal field by 

quadrangle, township, and ownership ................................................................................... 43

 12. Identified and hypothetical coal resources for the FGD zone of the 

Fairfield Group, Williams Fork Formation, Danforth Hills coal field by 

county, reliability, overburden, and coal-thickness.............................................................. 44

 13. Identified and hypothetical coal resources for the FGE zone of the 

Fairfield Group, Williams Fork Formation, Danforth coal field by 

quadrangle, township, and ownership ................................................................................... 45

 14. Identified and hypothetical coal resources for the FGE zone of the 

Fairfield Group, Williams Fork Formation, Danforth Hills coal field by 

county, reliability, overburden, and coal-thickness.............................................................. 46

 15. Identified and hypothetical coal resources for the FGF zone of the 

Fairfield Group, Williams Fork Formation, Danforth coal field by 

quadrangle, township, and ownership ................................................................................... 47
 16. Identified and hypothetical coal resources for the FGF zone of the 

Fairfield Group, Williams Fork Formation, Danforth Hills coal field by 

county, reliability, overburden, and coal-thickness.............................................................. 48

 17. Identified and hypothetical coal resources for the FGG zone of the 

Fairfield Group, Williams Fork Formation, Danforth coal field by 

quadrangle, township, and ownership. .................................................................................. 49

 18. Identified and hypothetical coal resources for the FGG zone of the 

Fairfield Group, Williams Fork Formation, Danforth Hills coal field by 

county, reliability, overburden, and coal-thickness.............................................................. 50

 19. Identified and hypothetical coal resources for the 

Fairfield Coal Group of the Upper Cretaceous, Williams Fork Formation, 

Danforth Hills coal field, Colorado by overburden, county, township, 

quadrangle, and ownership...................................................................................................... 51

Metric Conversion Factors

[Data in this volume are reported in customary inch-pound units because the metric system is not currently 

in use by the coal industry of the United States. Readers wishing to convert measurements to the 

International System of units (SI) may use the following factors] 

U.S. customary unit SI conversion 

Acre = 4,046.87 square meters 

Acre-foot = 1,233.49 cubic meters 

British thermal unit (Btu) = 1,055.056 joules 

Btu/lb = 2,326 joules per 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 

Square miles (mi2) = 2.59 square kilometers 

Short ton/acre-foot = 0.7355 kilograms per cubic meter 
Abstract

The assessment of coal resources in the Fairfi eld coal 

group, Danforth Hills coal fi eld, Moffat and Rio Blanco Counties, Colorado, is part of the U.S. Geological Survey’s (USGS) 

“National Coal Resource Assessment” (NCRA) Project, a 

5-year program to identify and characterize coal deposits that 

could potentially provide fuel for the Nation’s coal-derived 

energy needs during the fi rst quarter of the 21st century. For 

this project, the Nation is divided into nine regions, one of 

which encompassed the Rocky Mountains and Colorado Plateau. One of the priority subareas for resource assessment 

in the Rocky Mountains and Colorado Plateau region is the 

Danforth Hills coal fi eld that is located along the northeastern 

margin of the Piceance Basin.

Coal zones targeted for assessment in the Danforth Hills 

coal fi eld are in the Fairfi eld coal group and occur in the lower 

part of the Williams Fork Formation of the Upper Cretaceous 

Mesaverde Group. The coal beds in these zones are laterally 

discontinuous, are considered to be low sulfur (averaging 0.47 

percent), and have an apparent rank of high-volatile C bituminous when compared to many other coal-bearing regions in the 

United States. The coal quantities estimated for the Fairfi eld 

coal group are only in the identifi ed and hypothetical resource 

categories and represent the total net coal in beds greater than 

1.2 ft thick.

The Fairfi eld coal group contains an estimated coal 

resource of 21 billion short tons in seven coal zones of which 

more than 60 percent of the total coal is contained within the 

1,000-ft maximum overburden category. More than 90 percent 

of the total is federally owned. The coal resources estimated 

for Danforth Hills coal fi eld do not include the area inside 

the Colowyo Federal and State coal leases and the Preference 

Right Lease Application (pending Federal coal lease) nor do 

they refl ect economic, land-use, environmental, technological, 

and geologic constraints that may ultimately affect the availability and recoverability of the coal. The amount of recoverable coal is not addressed in this study. Important factors 

affecting recoverability are (1) a signifi cant amount of the 

coal is found at depths greater than 1,000 ft and (2) many of 

the coal beds are in close proximity stratigraphically, which 

may restrict underground mining of some beds. Coal can be 

bypassed due to longwall mining methods related to reduced 

thickness from partings and splits. Currently, coal is being 

mined at the Colowyo mine by dragline, and truck and shovel 

methods, and is transported by rail line to the Denver Rio 

Grande Railroad lines at Craig, Colo.

Introduction

Purpose and Scope

The assessment of the distribution and resources of the 

coal in the Danforth Hills coal fi eld of northwest Colorado is 

part of the U.S. Geological Survey’s National Coal Resource 

Assessment (NCRA) Project, which was initiated in 1994. 

The primary goal of the NCRA project is to characterize the 

resource potential and quality of coal resources for areas in the 

United States that will be utilized for the next few decades. 

The Danforth Hills coal fi eld (fi gs. 1 and 2), in Moffat and Rio 

Blanco Counties, is one of the priority areas within the Rocky 

Mountains and Colorado Plateau region. To restrict the resource 

assessment in the context of a 10- to 20-year development 

period, only coals in the Fairfi eld coal group (Hancock and Eby, 

1930) of the Williams Fork Formation of the Upper Cretaceous 

Mesaverde Group were assessed for this study (fi g. A on pl. 1 

and fi g. 3). The Fairfi eld coal group contains many of the thickest and potentially economic coal beds in the Danforth Hills 

coal fi eld. Study areas were determined by analyzing current 

mining activity, coal ownership, and by discussions with the 

U.S. Bureau of Land Management (BLM). This study area 

was selected because it contains active mining, large amounts 

of federally administered lands, and has potential for future 

Assessment of the Distribution and Resources 

of Coal in the Fairfi eld Coal Group of the 

Williams Fork Formation, 

Danforth Hills Coal Field, Northwest Colorado

By M.E. Brownfi eld, L.N.R. Roberts, E.A. Johnson, and T.J. Mercier

M1
development. Mineral rights to more that 90 percent of coal 

within the study area are owned by the U.S. Government. One 

mine (Kennecott’s Colowyo mine) is presently operating in the 

study area and produces coal from the Fairfi eld coal group.

The assessment of the Fairfi eld coal group in the Danforth 

Hills coal fi eld is based largely on data derived from geologic 

mapping, outcrop measurements, and drilling conducted in the 

study area by the U.S. Geological Survey (USGS) since the early 

1900’s. The coal-resource data has been stored digitally and 

manipulated in a Geographic Information System to calculate 

coal resources within a variety of spatial parameters that were 

deemed useful for land-use planning and potential mining. The 

major coal deposits in the Danforth Hills coal fi eld are present 

in the Upper Cretaceous Iles and Williams Fork Formations of 

the Mesaverde Group (fi gs. 3 and 4). Coal resources reported 

in this study are for total net coal and assessed coal zones in 

the Fairfi eld coal group of the Williams Fork Formation and 

represent only a part of the total in-place coal for the Danforth 

Hills coal fi eld. The Colowyo Coal Company’s Federal and State 

coal leases and their pending Preference Right Lease Application (PRLA) were excluded in this study (fi g. B on pl. 1).

Location

The Danforth Hills coal fi eld (fi g. 1 and fi g. A on pl. 1) 

is situated in northwest Colorado, in Moffat and Rio Blanco 

Counties, and is within the Rocky Mountain Coal Province of 

Tully (1996). The coal fi eld lies north of the White River along 

the northeastern margin of the Piceance Basin (fi g. 1), south and 

west of the Axial Basin, and east of the Lower White River coal 

fi eld along the northern extension of the Grand Hogback (fi g. 

2). The area is characterized by north- and east-trending ridges 

separated by steep canyons on the north, and to the south and 

west by steeply dipping, long and narrow hogbacks. Elevations 

in the coal fi eld range from 6,200 to 8,700 ft. Northward 

drainage is to the Yampa River and southward drainage is to 

the White River. The Flat Tops highlands of the White River 

Plateau (fi g. 2) to the southeast ranges in elevation from 8,500 

to 12,000 ft.

Figure 1. Map showing the locations of the Danforth Hills, Lower White River, and Yampa coal fi elds in Moffat, Rio Blanco, and Routt 

Counties, Colorado.

Colorado

0 50 100 Miles

Piceance Basin

OURAY

MONTROSE

DELTA

GUNNISON

MESA

PITKIN

EAGLE

ROUTT

GARFIELD

RIO BLANCO

MOFFAT

Yampa Danforth Hills

Sand Wash Basin

Lower White River

Dinosaur National 

Monument

Delta

Paonia Crested Butte Somerset

Grand Junction

Grand Mesa

Marble 

Redstone

Woody Creek

Basalt Carbondale Parachute

Rifle Glenwood Springs

New Castle

Rio Blanco

Meeker Rangely

Dinosaur



Axial Basin

M2 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Figure 2. Generalized geologic map of northwest Colorado showing outcrops of the coal-bearing Mesaverde Formation and Group and major 

coal fi elds within the eastern Sand Wash and Piceance Basins.

Crested Butte

Somerset 

Grand Mesa

Carbondale 

Book Cliffs

Lower White River

Grand

Hogback

Danforth Hills

 Yampa 

10 0 50 Miles

Intrusive rocks

Mesaverde Formation or

Group coal-bearing rocks

Map Explanation

Tertiary

Upper Cretaceous

Monocline

Fault - bar on

downthrown side

Anticline

Syncline

Piceance Basin

Eastern

Sand Wash Basin Grand

Hogback

Moncline

Axial Basin Anticline

109 ̊00'

40 ̊30'

40 ̊00'

39 ̊30'

39 ̊00'

108 ̊00' 107 ̊00' White River Plateau

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M3
Previous Geologic Studies and Mining Activity

Since the early 1900’s the USGS has conducted investigations to study the geology and to assess the coal, oil and 

gas, and oil-shale resources in Colorado. Gale (1907, 1909, 

1910) was the fi rst to investigate the coal resources in the 

Danforth Hills coal fi eld. Hancock (1925) and Hancock and 

Eby (1930) conducted the fi rst detailed geologic investigations 

in the Danforth Hills from 1911 to 1913. Detailed geologic 

mapping of the Danforth Hills was completed by Nutt (1981), 

Reheis (1981, 1983a, 1983b), and Izett and others (1983, 

1985). Additional mapping in the Danforth Hills was conducted by Dyni (1966), Collins (1976), and Pipiringos and 

Rosenlund (1977). 

Early mining activity in the Danforth Hills was limited 

because the closest railroad lines were more than 50 miles 

away. However, during the late 1800’s and early 1900’s, several mines in the Danforth Hills coal fi eld produced coal for 

local utilization. In addition to local heating uses, some of the 

coal provided fuel for the Meeker electric plant, nearby lumber 

mills, and blacksmith shops (Hancock, 1925). Gale (1910) 

reported quality analyses of coal from several of the mines. 

Coal is currently mined in the Danforth Hills coal fi eld by 

surface methods at the Colowyo mine, operated by Kennecott 

Corporation. The coal is mined from nine beds in the upper 

two coal zones of the Fairfi eld coal group of the Williams Fork 

Formation by dragline, and by truck and shovel methods, then 

shipped by a private rail to the Denver Rio Grande rail lines at 

Figure 3. Generalized regional cross section showing stratigraphic correlations and facies relationships for part of the Upper Cretaceous 

and Tertiary rocks in the Danforth Hills, Lower White River, and Yampa coal fi elds, northwest Colorado. Modifi ed from Brownfi eld and Johnson 

(1984).

Iles Fm.

Iles Fm.

Williams Fork Fm.

Williams Fork Fm.

Lewis Shale Lance Fm. Fort Union Fm.

Fort Union

Fm.

Wasatch Fm.

Wasatch

Fm.

Eocene Paleocene Upper Cretaceous

Mancos Shale (part)

Fox Hills Sandstone

Lower White River coal field Danforth Hills coal field Western Yampa coal field 

Castlegate Ss.

of the Mesaverde Group

Mesaverde Group

coal unit

lower unit

upper unit

Upper Cretaceous Paleocene-Eocene

Fort Union Fm.

Black Diamond

coal group

Lower

coal group

Fairfield coal group

Goff coal group

Barren interval

Lion Canyon

Ss. Mbr.

Lion Canyon

coal group

Tow Creek Ss. Mbr.

Trout Creek Ss. Mbr.

Twentymile Ss. Mbr.

Mancos Shale (part)

lower coal group

middle coal group

upper coal group

marine shale

marine shale

Sego Ss.

Mancos

Sh. (part)

1000 Ft

Lewis Shale

Wasatch Fm.

(part)

? ?

West East

rimrock ss.

?

?

Lower White

River

Danforth

Hills

Yampa 

Inset

Line of

section

Alluvial, coastal plain, and mire

Upper shoreface 

and estuarine

Lower shoreface and 

offshore marine

Depositional environments

?

?

M4 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Iles Formation

of the Mesaverde Group

Williams Fork Formation

of the Mesaverde Group Wasatch Fm. Fort Union Fm.

Paleocene-Eocene Upper Cretaceous

MancosSh.(part)

Black Diamond

coal group

lower

coal group

Fairfield coal

group

Goff coal

group

barren interval

Lion Canyon Ss. Mbr.- 

Lion Canyon

coal group

Trout Creek Ss. Mbr.

FGA

FGB

FGC

FGD

FGE

FGF

FGG

1000 feet

250 feet

Yampa bed

vvvvvvvvvvv Yampa bed

vvvvvvvvvvv

Alluvial, coastal plain, and mire

Upper shoreface 

and estuarine

Lower shoreface and 

offshore marine

Depositional environments

Figure 4. Generalized stratigraphic column showing depositional environments for a portion the Upper 

Cretaceous and Tertiary rocks in the Danforth Hills coal fi eld, Colorado. Shown are the major divisions 

of the Fairfi eld coal group and the Yampa bed of the Williams Fork Formation. Yampa bed not drawn 

to scale.

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M5
Craig, Colo. Coal production averaged 4.5 million short tons 

per year from 1989 to 1996 (Resource Data International, 

Inc., 1998). In 1997, the Colowyo mine produced 4.3 million 

short tons of coal, accounting for 18 percent of the 24 million 

short tons of coal produced in northwest Colorado (Resource 

Data International, Inc., 1998). Future coal production in the 

Colowyo mine will probably be limited to the upper part of 

the Fairfi eld coal group and potential new mines are expected 

to be located in the Fairfi eld coal group as well. Because of 

limited access to the Danforth Hills area by rail, new mining 

activity will likely be restricted to localities adjacent to the 

Colowyo mine.

Methods

In order to assess the coal resources of the Danforth Hills 

coal fi eld, we created digital fi les for storing data on various 

geologic and other features such as outcrop lines, elevation data, 

coal thickness, faults, fold axes, and extent of Federal coal leases 

and mined-out areas within the study area. Drill-hole data have 

been stored and analyzed in a relational stratigraphic database 

and graphics software package (Stratifact, GRG Corporation, 

Denver, Colo., 1997). Digital fi les of the publicly available drill 

holes are provided in Appendix 1 of this chapter, which is on disc 

2 of this CD-ROM. Mean coal-zone thicknesses and elevation 

data, derived from the Stratifact drill-hole database, were 

integrated with digital elevation data to derive the Fairfi eld coalzone outcrop lines (Roberts and others, chap. C, this CD-ROM). 

These outcrop lines were then used to defi ne assessment areas 

for the study. The drill-hole data were analyzed by USGS 

computer program (G.D. Stricker, written commun., 1998) 

to determine net-coal-bed thickness, after Wood and others 

(1983). The digital fi les were stored, analyzed, and manipulated 

in a Geographic Information System (GIS) using ARC/INFO 

(Environmental Systems Research Institute, Inc.) software. 

Gridding, and subsequent generation of contour and isopach 

maps, was done with EarthVision (Dynamic Graphics, Inc.) 

software, and the contours were converted to ARC/INFO 

coverages using custom programs ISMARC and ConvertISM.AML (Roberts and others, 1998). This software integrated 

the various coverages, allowing us to calculate coal resources 

and characterize coal distribution within a variety of geologic 

and geographic parameters. The various digital coverages used 

in this report are available in the ArcView project in Appendix 

2, and they are explained by Biewick and Mercier (chap. D, this 

CD-ROM). The methodology for reporting the estimated coal 

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

more detail in the methodology chapter of this report (Roberts 

and others, chap. C, this CD-ROM).

Geologic Maps

Digital geologic maps of the study area were generated 

using ARC/INFO coverages that included stratigraphic unit 

boundaries and elevations, faults, fold axes, and coal thicknesses. Data from the 1:500,000-scale geologic map of Colorado (Tweto, 1979; Green, 1992) were used to generate digital regional maps of northwest Colorado (fi g. 2). The studyarea portion of Colorado geologic map was compiled from 

1:250,000-scale geologic maps (Tweto 1975, 1976; Rowley 

and others, 1979) and published at a scale of 1:500,000. The 

geologic map for the Danforth Hills coal fi eld was compiled at 

a scale of 1:62,500 and modifi ed from 1:62,500-scale maps by 

Hancock (1925), Hancock and Eby (1930), Barnum and others 

(1974), and Izett and others (1985), and from 1:24,000-scale 

maps by Nutt (1981), and Reheis (1981, 1983a, 1983b). The 

1:62,500-scale map was then reduced to the map shown on 

plate 1 (see fi g. A on pl. 1).

Geographical Boundaries

Geographic boundary coverages were imported from 

existing public-domain databases. Surface and mineral ownership were obtained from 1:24,000-scale digital compilations 

completed by the Craig District Offi ce, BLM. County and 

State lines were obtained from 1:100,000-scale Topologically 

Integrated Geographic Encoding and Referencing (TIGER) 

fi les produced by the U.S. Bureau of the Census in 1990. 

Surface topography was obtained from 1:24,000 Digital Elevation Model (DEM) fi les for the 7.5-minute quadrangles within 

the study area (fi g. 5). Coal-lease boundaries were obtained 

from the U.S. Bureau of Land Management and compiled 

digitally by the USGS.

Geophysical Logs

More than 640 borehole geophysical logs, supplied in part 

by the BLM, were used in this study. Table 1 lists information 

on 110 of the publicly available exploratory drill holes. Fiftysix of these holes were drilled from 1976 to 1979 by the 

U.S. Geological Survey. Another 52 holes were obtained from 

expired coal leases, and two are oil and gas exploration holes. 

Figure B on plate 1 shows drill-hole locations with index 

numbers that are cross-referenced with the hole number in 

table 1. Data on the other drill holes in the Danforth Hills 

coal fi eld are proprietary and were obtained over a 25-year 

drilling period by several different operators and organizations, 

commonly at different scales. Coal and other lithologic units 

are readily identifi ed on the geophysical logs because good 

natural gamma and density traces are recorded on them. The 

log quality allowed unit boundaries generally to be picked to 

the nearest 1⁄2 ft. A few of the older, lower quality logs allowed 

interpretations to the nearest foot, but a few of the most recent, 

well-calibrated logs allowed unit picks to the nearest one-tenth 

of a foot.

As in most coal studies, the degree of certainty in establishing coal-bed correlations varies with distance between control points (the higher the drilling density, the better the correM6 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
CITADEL PLATEAU 

PRICE CREEK 

EASTON GULCH 

MONUMENT BUTTE 

CEDAR KNOB

JUNIPER MOUNTAIN

DEVILS HOLE GULCH 

THORNBURGH 

MEEKER 

SAWMILL MOUNTAIN 

RATTLESNAKE MESA 

NINEMILE GAP

WHITE ROCK 

AXIAL

Moffat County

Rio Blanco County

Alluvial deposits (Quaternary),

Browns Park, Green River,

Wasatch Fms. (Tertiary), and

Mancos Shale (Cretaceous)

Iles and Williams Fork

Formations and Mancos Shale

Map Explanation

County line

Township boundary

Quadrangle boundary

R. 96 W. R. 95 W.

R. 94 W.

T. 5 N.

T. 6 N.

R. 93 W. R. 92 W.

T. 4 N.

T. 2 N.

T. 1 N.

T. 3 N.

T. 1 S.

1 0 5 Miles

Figure 5. Index map showing location of the Danforth Hills coal fi eld with respect to the 7.5’ topographic quadrangles. Outline of the Danforth 

Hills coal fi eld drawn on the base of the Upper Cretaceous Iles Formation.

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M7
Table 1. Locations of coal exploration drill holes in the Danforth Hills coal field, northwest Colorado, for which data are publicly avaliable. 

[Index number shown on figure B, plate 1. Also shown for the holes are elevations, depth drilled, and quadrangle. Surface elevation and depth drilled are in feet; 

to convert feet to meters, multiply by 0.3048] 

Index 

no. 

Drill hole 

no. 

Latitude Longitude Sec Township Range 7.5’ quadrangle Elevation 

(feet) 

Depth drilled 

(feet) 

1 D-53EG 40.3229 107.96235 17 T. 4 N. R. 94 W. EASTON GULCH 7560 706 

2 D-51EG 40.31652 107.93306 15 T. 4 N. R. 94 W. EASTON GULCH 7080 1510 

3 D-38EG 40.31292 107.97329 18 T. 4 N. R. 94 W. EASTON GULCH 7895 1080 

4 D-44EG 40.29633 107.90723 23 T. 4 N. R. 94 W. EASTON GULCH 6990 1320 

5 D-49EG 40.29474 107.95667 29 T. 4 N. R. 94 W. EASTON GULCH 7260 1425 

6 D-47A 40.28484 107.82436 28 T. 4 N. R. 93 W. AXIAL 6980 715 

7 D-39EG 40.27864 107.93852 33 T. 4 N. R. 94 W. EASTON GULCH 6895 800 

8 D-41EG 40.27829 107.91592 34 T. 4 N. R. 94 W. EASTON GULCH 6980 820 

9 D-42EG 40.27805 107.96646 32 T. 4 N. R. 94 W. EASTON GULCH 7400 700 

10 D-40EG 40.27699 107.92591 34 T. 4 N. R. 94 W. EASTON GULCH 7290 1453 

11 D-47A1 40.27566 107.83014 33 T. 4 N. R. 93 W. AXIAL 7045 975 

12 D-56A 40.27499 107.80896 34 T. 4 N. R. 93 W. AXIAL 7200 1430 

13 D-45EG 40.26531 107.94592 4 T. 3 N. R. 94 W. EASTON GULCH 7050 840 

14 D-50EG 40.26158 107.92715 3 T. 3 N. R. 94 W. EASTON GULCH 7200 620 

15 D-26A 40.25948 107.84076 5 T. 3 N. R. 93 W. AXIAL 7327.5 500 

16 #1 GOSSARD 40.25602 107.82337 4 T. 3 N. R. 93 W. AXIAL 7357 8785 

17 D-11A 40.25235 107.84564 5 T. 3 N. R. 93 W. AXIAL 7560.8 1140 

18 D-03A 40.25068 107.87005 7 T. 3 N. R. 93 W. AXIAL 7620 900 

19 D-31NG 40.2492 107.8599 7 T. 3 N. R. 93 W. NINEMILE GAP 6917 200 

20 D-52D 40.24872 107.95106 9 T. 3 N. R. 94 W. DEVILS HOLE GULCH 7200 600 

21 D-06NG 40.24576 107.79421 11 T. 3 N. R. 93 W. NINEMILE GAP 7240 1583 

22 D-43DH 40.24483 107.97887 7 T. 3 N. R. 94 W. DEVILS HOLE GULCH 7400 560 

23 D-27NG 40.24468 107.85122 8 T. 3 N. R. 93 W. NINEMILE GAP 7774.1 500 

24 D-01NG 40.23941 107.76081 7 T. 3 N. R. 92 W. NINEMILE GAP 7250 1102 

25 D-29NG 40.23922 107.86176 7 T. 3 N. R. 93 W. NINEMILE GAP 7257.8 381 

26 D-34NG 40.23887 107.7917 11 T. 3 N. R. 93 W. NINEMILE GAP 6700 200 

27 D-12NG 40.2385 107.85236 8 T. 3 N. R. 93 W. NINEMILE GAP 7913.6 1240 

28 D-54D 40.23737 107.94241 9 T. 3 N. R. 94 W. DEVILS HOLE GULCH 8120 940 

29 D-07NG 40.23682 107.81922 15 T. 3 N. R. 93 W. NINEMILE GAP 7747 1675 

30 D-35NG 40.23418 107.86255 18 T. 3 N. R. 93 W. NINEMILE GAP 7514.7 380 

31 D-02NG 40.23327 107.8553 17 T. 3 N. R. 93 W. NINEMILE GAP 8018.7 800 

32 D-20NG 40.23306 107.84364 17 T. 3 N. R. 93 W. NINEMILE GAP 7991.1 520 

33 D-18NG 40.23047 107.81049 15 T. 3 N. R. 93 W. NINEMILE GAP 7480 540 

34 D-04NG 40.23037 107.75639 18 T. 3 N. R. 92 W. NINEMILE GAP 7000 1171 

35 D-28NG 40.2273 107.86126 18 T. 3 N. R. 93 W. NINEMILE GAP 7780 280 

36 D-19NG 40.22453 107.84029 17 T. 3 N. R. 93 W. NINEMILE GAP 8095 520 

37 D-24NG 40.22449 107.86777 18 T. 3 N. R. 93 W. NINEMILE GAP 8336.2 220 

38 D-17NG 40.22323 107.82707 16 T. 3 N. R. 93 W. NINEMILE GAP 7827 500 

39 D-32NG 40.22187 107.81128 22 T. 3 N. R. 93 W. NINEMILE GAP 6885 220 

40 D-25NG 40.22185 107.85228 20 T. 3 N. R. 93 W. NINEMILE GAP 8241.8 540 

41 D-37DH 40.22151 107.99056 19 T. 3 N. R. 94 W. DEVILS HOLE GULCH 8080 715 

42 D-33NG 40.22119 107.867 19 T. 3 N. R. 93 W. NINEMILE GAP 8243 600 

43 D-05NG 40.2195 107.76436 24 T. 3 N. R. 93 W. NINEMILE GAP 7345 1235 

44 D-23NG 40.21922 107.86302 19 T. 3 N. R. 93 W. NINEMILE GAP 8441.8 500 

45 D-10NG 40.21869 107.84266 20 T. 3 N. R. 93 W. NINEMILE GAP 8114.3 1480 

46 D-22NG 40.21622 107.8525 20 T. 3 N. R. 93 W. NINEMILE GAP 8228 500 

47 D-48NG 40.21429 107.86422 19 T. 3 N. R. 93 W. NINEMILE GAP 8411 1200 

48 D-16NG 40.21276 107.83113 21 T. 3 N. R. 93 W. NINEMILE GAP 7443.6 518 

49 D-21NG 40.21075 107.84955 20 T. 3 N. R. 93 W. NINEMILE GAP 7983.4 560 

50 D-58NG 40.20518 107.87 30 T. 3 N. R. 93 W. NINEMILE GAP 8155.3 660 

51 D-62NG 40.20318 107.84271 29 T. 3 N. R. 93 W. NINEMILE GAP 7105.1 320 

52 D-61NG 40.20152 107.8511 29 T. 3 N. R. 93 W. NINEMILE GAP 7225.5 275 

53 D-60NG 40.19709 107.87215 30 T. 3 N. R. 93 W. NINEMILE GAP 8006.5 400 

54 D-13NG 40.19594 107.8343 28 T. 3 N. R. 93 W. NINEMILE GAP 7855 500 

55 D-14NG 40.19436 107.84436 29 T. 3 N. R. 93 W. NINEMILE GAP 7815 500 

56 75-M-184 40.18805 107.83736 33 T. 3 N. R. 93 W. NINEMILE GAP 7948.2 1100

M8 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Table 1. Locations of coal exploration drill holes in the Danforth Hills coal field, northwest Colorado, for which data are publicly avaliable—

Continued. 

Index 

no. 

Drill hole 

no. 

Latitude Longitude Sec Township Range 7.5’ quadrangle Elevation 

(feet) 

Depth drilled 

(feet) 

57 K15-CD-79 40.18023 107.85085 32 T. 3 N. R. 93 W. NINEMILE GAP 8125 1085 

58 D-08NG 40.15764 107.75801 7 T. 2 N. R. 92 W. NINEMILE GAP 8490 1231 

59 75-M-172 40.15664 107.82444 9 T. 2 N. R. 93 W. NINEMILE GAP 7701.1 700 

60 74-M-169 40.15588 107.82207 9 T. 2 N. R. 93 W. NINEMILE GAP 7401.3 700 

61 75-M-171 40.15143 107.82865 9 T. 2 N. R. 93 W. NINEMILE GAP 7510.6 100 

62 75-M-174 40.14857 107.82647 16 T. 2 N. R. 93 W. NINEMILE GAP 7622.4 1000 

63 77-M-211 40.14239 107.82757 16 T. 2 N. R. 93 W. NINEMILE GAP 7172.7 2578 

64 74-M-163 40.14037 107.8212 16 T. 2 N. R. 93 W. NINEMILE GAP 7165.5 860 

65 76-M-199 40.13683 107.82968 16 T. 2 N. R. 93 W. NINEMILE GAP 7051.7 2700 

66 HFC-5 40.13563 107.81944 21 T. 2 N. R. 93 W. NINEMILE GAP 7150 679 

67 70-M-002 40.13408 107.80002 23 T. 2 N. R. 93 W. NINEMILE GAP 7407.6 1000 

68 74-M-164C 40.13316 107.79113 23 T. 2 N. R. 93 W. NINEMILE GAP 7434 270 

69 HFC-4A 40.13013 107.83968 20 T. 2 N. R. 93 W. NINEMILE GAP 6978 110 

70 79-23 40.1297 107.82768 21 T. 2 N. R. 93 W. NINEMILE GAP 7249.4 251 

71 79-17 40.12924 107.83619 21 T. 2 N. R. 93 W. NINEMILE GAP 7170.9 2635 

72 75-M-175 40.12905 107.76387 24 T. 2 N. R. 93 W. NINEMILE GAP 7154.3 634 

73 77-M-207 40.12881 107.79258 23 T. 2 N. R. 93 W. NINEMILE GAP 7629.5 2756 

74 76-M-204 40.12812 107.77314 24 T. 2 N. R. 93 W. NINEMILE GAP 7445.7 2020 

75 74-M-152 40.12646 107.78214 24 T. 2 N. R. 93 W. NINEMILE GAP 7567.8 1001 

76 74-M-153 40.12506 107.79494 23 T. 2 N. R. 93 W. NINEMILE GAP 7863.7 1000 

77 74-M-160 40.12425 107.77066 24 T. 2 N. R. 93 W. RATTLESNAKE MESA 7717.9 1050 

78 76-M-198 40.12315 107.78997 23 T. 2 N. R. 93 W. NINEMILE GAP 7619 1995 

79 74-M-151 40.11946 107.82884 28 T. 2 N. R. 93 W. RATTLESNAKE MESA 7414 1100 

80 HRP-1 40.11881 107.84462 29 T. 2 N. R. 93 W. RATTLESNAKE MESA 6925.2 701 

81 76-M-195 40.11747 107.77728 25 T. 2 N. R. 93 W. RATTLESNAKE MESA 7876.8 1485 

82 80-08C 40.11738 107.83514 28 T. 2 N. R. 93 W. RATTLESNAKE MESA 7532.7 1475 

83 79-13 40.11725 107.82793 28 T. 2 N. R. 93 W. RATTLESNAKE MESA 7499 1564 

84 77-NNG-04 40.117 107.84733 29 T. 2 N. R. 93 W. RATTLESNAKE MESA 6940 1600 

85 77-M-210A 40.11663 107.76616 25 T. 2 N. R. 93 W. RATTLESNAKE MESA 7542.1 1250 

86 80-04 40.11642 107.81915 28 T. 2 N. R. 93 W. RATTLESNAKE MESA 7681.9 1700 

87 77-NNG-07C 40.11604 107.84023 29 T. 2 N. R. 93 W. RATTLESNAKE MESA 7541 1800 

88 HRJ-1 40.11598 107.84509 29 T. 2 N. R. 93 W. RATTLESNAKE MESA 6915.5 204 

89 77-NNG-01C 40.11549 107.8538 29 T. 2 N. R. 93 W. RATTLESNAKE MESA 7664 1820 

90 74-M-161 40.11467 107.80488 27 T. 2 N. R. 93 W. RATTLESNAKE MESA 7686.3 780 

91 77-NNG-05C 40.11452 107.84787 29 T. 2 N. R. 93 W. RATTLESNAKE MESA 6940 1120 

92 HRG-1 40.1141 107.84524 29 T. 2 N. R. 93 W. RATTLESNAKE MESA 6910.8 182 

93 D-09RM 40.11371 107.76102 30 T. 2 N. R. 92 W. NINEMILE GAP 7025 761 

94 79-08 40.11341 107.83526 28 T. 2 N. R. 93 W. RATTLESNAKE MESA 7707.8 868 

95 76-M-203 40.11309 107.83714 28 T. 2 N. R. 93 W. RATTLESNAKE MESA 7709.1 1460 

96 74-M-159 40.11283 107.79058 26 T. 2 N. R. 93 W. RATTLESNAKE MESA 8104.9 906 

97 80-06C 40.11281 107.82345 28 T. 2 N. R. 93 W. RATTLESNAKE MESA 7990 1148 

98 77-NNG-10 40.11216 107.84886 29 T. 2 N. R. 93 W. RATTLESNAKE MESA 6960 1220 

99 77-NNG-02C 40.11173 107.85671 29 T. 2 N. R. 93 W. RATTLESNAKE MESA 7883.2 1340 

100 80-03 40.11109 107.83517 28 T. 2 N. R. 93 W. RATTLESNAKE MESA 7851.6 1000 

101 76-M-194A 40.1109 107.77672 25 T. 2 N. R. 93 W. RATTLESNAKE MESA 8170.9 778 

102 77-NNG-09 40.11029 107.83968 29 T. 2 N. R. 93 W. RATTLESNAKE MESA 7720 800 

103 80-12 40.10967 107.83163 28 T. 2 N. R. 93 W. RATTLESNAKE MESA 8024.3 660 

104 77-NNG-03 40.10925 107.85716 29 T. 2 N. R. 93 W. RATTLESNAKE MESA 7880 1220 

105 77-NNG-06A 40.10873 107.84856 29 T. 2 N. R. 93 W. RATTLESNAKE MESA 6920 990 

106 80-11 40.10692 107.82769 28 T. 2 N. R. 93 W. RATTLESNAKE MESA 8143 580 

107 76-M-196 40.10681 107.79196 26 T. 2 N. R. 93 W. RATTLESNAKE MESA 8330.7 1465 

108 68-M-016 40.10678 107.80705 27 T. 2 N. R. 93 W. RATTLESNAKE MESA 7559.5 655 

109 77-M-208B 40.10428 107.77509 36 T. 2 N. R. 93 W. RATTLESNAKE MESA 8102.8 1560 

110 74-M-154 40.09947 107.79502 35 T. 2 N. R. 93 W. RATTLESNAKE MESA 8559 512 

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M9
lation), local stratigraphy, presence or absence of stratigraphic 

markers, and log quality. Although correlations of individual 

coal beds should generally be regarded as indications of stratigraphic position within coal zones, the lithologic and stratigraphic log interpretations resulting from the present study 

are considered to refl ect an accurate representation of the 

stratigraphic framework of coal beds that exist within the 

Danforth Hills area. 

Acknowledgments

We would like to thank Janet Hook, Craig District Offi ce, 

BLM, for supplying coal-exploration drill-hole data, land-use 

data, and leasing information for the study area, and Matt 

McMcolm, Colorado State Offi ce, BLM, for confi rming the 

lease maps. We want to gratefully acknowledge Bruce Barnum 

(Sage Discovery, Golden, Colo.) for his geologic data and 

valuable discussions on the study area. 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 contractors Tim 

Gognat, Al Heinrich, Jon Haacke, and Marin Popov are 

acknowledged for their technical support with drill-hole databases and computer graphics. In addition, we would like to 

thank USGS employees Ronald Affolter, Stephen Roberts, and 

William Keefer for their peer reviews of the manuscript, and 

Rick Scott for his editorial work.

Geologic Setting

Stratigraphy of the Cretaceous and 

Tertiary Strata of the Danforth Hills Coal Field

All of the coal stratigraphic units exposed within the 

Danforth Hills coal fi eld are of Upper Cretaceous and Tertiary 

age (fi g. 3), with all the coal-bearing rocks considered in this 

study confi ned to the Upper Cretaceous Mesaverde Group. 

The lowest unit is the thick marine Mancos Shale of Early 

to Late Cretaceous age, which is overlain by the mostly nonmarine, coal-bearing Iles and Williams Fork Formations of 

the Mesaverde Group. A generalized columnar section for the 

Danforth Hills coal fi eld is shown in fi gure 4. The Mesaverde 

Group generally consists of a thinly to thickly interbedded succession of shale, siltstone, and sandstone deposited largely 

in a terrestrial environment, although regional relations indicate that this sedimentation was directly infl uenced by sealevel changes. Carbonaceous rocks are common, and thick 

beds of coal occur throughout the Williams Fork Formation. 

Rocks of marine or marginal-marine origin do occur within 

the Mesaverde Group, most notably the Trout Creek Sandstone 

Member at the top of the Iles Formation (fi gs. 3 and 4). 

This persistent marginal-marine sandstone is one of the best 

stratigraphic markers in the area. It is directly overlain by the 

Fairfi eld coal group (Hancock and Eby, 1930), which contains 

the most extensive coal resources in the area. 

The Iles Formation averages about 1,500 ft thick in the 

Danforth Hills coal fi eld. Thick ledge-forming sandstones are 

the most notable feature of the Iles when observed in outcrop. 

Thin coals occur throughout the formation and locally reach 

signifi cant thickness and continuity in the Black Diamond coal 

group (Hancock and Eby, 1930) and in the lower coal group 

(see Coal Geology of the Danforth Hills Coal Field section, 

this report). The Trout Creek Sandstone Member at the top 

of the Iles Formation averages about 75 ft in thickness in 

the central part of the Danforth Hills. The Trout Creek is 

a persistent, upward-coarsening, ledge-forming, light-colored 

sandstone that can be mapped over the entire study area. The 

Iles Formation correlates well to other areas of northwest 

Colorado, although the Trout Creek Member thins out and 

disappears to the west (fi g. 3). Thus, the Trout Creek cannot 

be used to separate of the Iles and the overlying Williams Fork 

(fi g. 3) in the Lower White River coal fi eld (Brownfi eld and 

others, chap. N, this CD-ROM).

The Williams Fork Formation is present at the surface 

over most of the study area, and it contains a large majority 

of the coal resources in the area. Hancock and Eby (1930) 

subdivided the Williams Fork into fi ve stratigraphic units: in 

ascending order, these are the Fairfi eld coal group, barren 

interval, Goff coal group, Lion Canyon Sandstone, and Lion 

Canyon coal group. Hancock and Eby (1930) estimated the 

Williams Fork to be 4,500 to 5,000 ft thick and to contain all 

of the signifi cant coal beds; thickness of 3,000 to 3,500 ft were 

considered to be a more reliable range for the present study. 

These large thicknesses relative to other areas of northwest 

Colorado are the result of structural and erosional relationships 

and to facies changes. The lower part of the barren interval 

correlates with the upper coal group of the Yampa coal fi eld 

(fi g. 3). The uppermost part of the Goff coal group of the 

Williams Fork Formation in the Danforth Hills coal fi eld is 

equivalent to the Lewis Shale–Fox Hills Sandstone succession 

(fi g. 3) in the Yampa coal fi eld to the north (Hancock and 

Eby, 1925). Marine units equivalent to the Lewis Shale are 

represented by a thin shale tongue that occurs below the Lion 

Canyon Sandstone, which is present along the western margin 

of the Danforth Hills; this shale, however, has been eroded 

from most of the study area. The shoreward facies of this 

marine unit is represented by the Lion Canyon Sandstone 

Member (fi g. 3), which is equivalent to the Fox Hills Sandstone in the western part of the Yampa coal fi eld. The 1,000 

ft of coal-bearing Williams Fork Formation overlying the Lion 

Canyon Sandstone in the western part of the Danforth Hills 

area represents an extension of the Lance Formation westward 

from the Yampa coal fi eld (Sears, 1925). Thin lenticular coals 

present in the Lance-equivalent rocks are included in the Lion 

Canyon coal group (fi g. 4) of Hancock and Eby (1930). No 

defi nite correlative unit to the Twentymile Sandstone Member 

(fi g. 3), an important marker unit in the Williams Fork to the 

M10 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
northeast in the Yampa coal fi eld, is present in the Danforth 

Hills coal fi eld.

The depositional setting of the Williams Fork Formation 

in the Danforth Hills was especially favorable for the formation of coal. The rocks were deposited along the western 

margin of the late Campanian to Maastrichtian Western Interior Seaway (Roberts and Kirschbaum, 1995), where, regionally, there was a stacking of several thousand feet of coalbearing strata along the coastal plain. During deposition of 

this strata, the area that is now northwest Colorado was at a 

latitude of about 42 degrees north (Roberts and Kirschbaum, 

1995) and had a humid, subtropical climate. This coupled 

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

depositional setting, was conducive to the development of a 

complex network of peat swamps. The resulting coal-bearing 

rocks typically show a cyclic pattern of coal deposition, which 

is now refl ected in the coal zones defi ned during the present 

study. Sedimentary processes associated with near-shore deposition and fl uvial deposition in the Danforth Hills area have 

infl uenced the geometry and distribution of these deposits.

Tertiary rocks in the Danforth Hills coal fi eld are 

restricted to the western margin of the study area along the 

Grand Hogback monocline (fi g. 2). Overlying the Upper Cretaceous rocks is a section of fl uvial and lacustrine rocks 

assigned to the Paleocene Fort Union Formation and Paleocene 

to Eocene Wasatch Formation (fi g. 3). Thin lenticular coals 

have been mapped in the Fort Union (Pipiringos and Rosenlund, 1977; Izett and others, 1985) but were not included in 

this study.

Structure

The Danforth Hills area lies along the northeastern fl ank 

of the Piceance Basin. The Grand Hogback monocline, a major 

structure, forms the eastern margin of the basin (fi g. A on pl. 

1 and fi g. 2). The study area lies northwest of the broad White 

River Plateau and directly south of the Axial Basin (fi gs. 1 and 

2), which can be considered an eastward extension of the Uinta 

Mountain uplift.

The study area is deformed by several major folds, as 

shown on a structure map drawn on the top of the Trout Creek 

Sandstone Member of the Iles Formation (fi g. A on pl. 1). The 

Sulphur Creek syncline trends generally east-west across the 

southern part of the area (fi g. A on pl. 1). The Danforth Hills 

anticline trends generally southeastward along the southwest 

margin of the study area where it is subparallel to the Grand 

Hogback monocline where dips commonly reach 45° (fi g. A 

on pl. 1 and fi g. 2). The anticline then turns eastward, paralleling the Sulphur Creek syncline. Structural relief of 2,000 to 

3,000 ft is common between the axes of these two folds (fi g. 

A on pl. 1). Strata on the fl anks of the Sulphur Creek syncline 

dip 10°–30°.

Structural deformation is less intense in the northern and 

northeastern part of the study area (fi g. A on pl. 1), and 

dips are generally less than 10° and commonly less than 5°. 

The Elkhorn syncline plunges north-northeast across the eastern margin from a structural “saddle” on the trend of the 

Danforth Hills anticline. Subparallel to the northern margin 

is the Collom syncline (Hancock, 1925). The northernmost 

margin of the study area coincides with the south fl ank of the 

Axial Basin anticline (Hancock, 1925).

Large-displacement faults are not common in the Danforth Hills area except for two faults cutting the northern 

extension of the Grand Hogback (fi g A on pl. 1). The northern 

fault has produced a distinct offset in the Trout Creek Sandstone and has an estimated vertical displacement of 510 ft 

(Hancock and Eby, 1930), whereas the southern fault has a 

vertical displacement of 285 ft. However, local faulting related 

to folding along the Danforth Hills anticline is common, and 

fracturing and minor displacements have accompanied the 

removal of thick coals by burning.

Older, published elevation and outcrop data for the Danforth Hills coal fi eld and adjacent areas is of uncertain quality 

because of the small-scale and now-obsolete methods used for 

preparing topographic bases (Gale, 1910). Perhaps the best 

sources for structural information for much of the study area 

are the Meeker quadrangle geologic map (1:62,500 scale) by 

Hancock and Eby (1930) and the Axial quadrangle geologic 

map (1:62,500 scale) by Hancock (1925) who constructed 

structure contours on the top the Trout Creek Sandstone 

Member of the Iles Formation. Geologic mapping and exploration drilling by Nutt (1981), Reheis (1976, 1978a, 1978b, 

1981, 1983a, 1983b), and Izett and others (1985) provided 

additional structural information for some parts of the study 

area. Information derived from an analysis of drill-hole data 

during the present study was used to further update and construct the fi nal structure contour map shown in fi gure A, 

plate 1.

Coal Geology of the 

Danforth Hills Coal Field

Stratigraphy

The coal-bearing intervals in the Iles and Williams Fork 

Formations of the Mesaverde Group in the Danforth Hills were 

stratigraphically subdivided into six coal units (see fi gs. 3 and 

4) by Hancock and Eby (1930). The Iles was subdivided into 

two units, the lower and the Black Diamond coal groups. The 

Williams Fork was subdivided into three coal units and one 

barren interval. In ascending order, these units are Fairfi eld 

coal group, the barren interval, the Goff coal group, and the 

Lion Canyon coal group.

Along the northern and eastern margins of the study 

area, thin coal beds occur in the lower coal group between 

100 to 250 ft above the base of the Iles Formation. The 

lower coal group consists of a few thin coal beds and thick 

beds of carbonaceous shale associated with thick, cliff-forming 

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M11
sandstones north of Meeker, Colo. (fi g. A on pl. 1). These coals 

were used for local consumption in the late 1800’s and are 

presently of little economic value. The principal coal beds of 

the Iles Formation occur in the upper part, within an interval 

from 150 to 350 ft below the top the Trout Creek Sandstone. 

This coal-bearing interval was named for the Black Diamond 

coal mine (Hancock and Eby, 1930) north of Meeker (fi g. A 

on pl. 1). The Black Diamond coal group commonly contains 

four to six coal beds that were extensively developed in the late 

1800’s and early 1900’s owing to their proximity to the town. 

This coal interval thins eastward and also has little current economic value. The Iles Formation is predominately terrestrial 

in origin and consists of thick beds of sandstone interbedded 

with mudstone, carbonaceous shale, and coals deposited in a 

coastal-plain environment.

The Williams Fork Formation contains the thickest and 

economically the most important coal beds in the Danforth 

Hills coal fi eld. Data from drill holes and geologic maps indicates that the formation is about 3,000 to 3,500 ft thick. Thickness of the Fairfi eld coal group at the base of the Williams 

Fork averages 1,300 ft (Hancock and Eby, 1930), but the complete interval was rarely penetrated in the drill holes studied. 

This coal group was named for the Fairfi eld mine near the 

town of Meeker (fi g. A on pl. 1 ). The Fairfi eld coal group 

is equivalent to the Cameo-Wheeler coal zone in the southern 

part of the Piceance Basin and to the Wheeler-Fairfi eld coal 

zone along the southern part of the Grand Hogback (Hettinger 

and others, chap. O, this CD-ROM). It is correlated to the 

middle coal group of the William Fork Formation (fi g. 2) in the 

Yampa coal fi eld (Johnson and others, chap. P, this CD-ROM). 

The Fairfi eld coal group is predominately terrestrial in origin 

and consists of thin to thick beds of sandstone interbedded 

with mudstone, carbonaceous shale, and coal deposited in a 

coastal-plain environment.

A regionally persistent tonstein (altered ash-fall tuff) 

named the Yampa bed by Brownfi eld and Johnson (1986) 

occurs in the lower part of the Fairfi eld coal group of the Williams Fork Formation (pl. 1, fi g. C and fi g. 4). Where exposed 

on the surface or observed in drill core, this unit is a white 

to grayish white structureless claystone. In the subsurface, it 

serves as an important regional marker bed that is easily identifi ed on geophysical logs. The Yampa bed ranges in thickness 

from less than 1 ft to more than 3 ft. In the central and western 

parts of the coal fi eld, the unit lies between 100 and 300 

ft above the top of the Trout Creek Sandstone, respectively. 

However, in the northern part of the coal fi eld the stratigraphic 

separation is less than 100 ft. The age of the Yampa bed, 

72.5±5.1 Ma, was determined using K-Ar dating methods on 

andesine. The tonstein was used to as a datum for the correlation of coal beds in the Fairfi eld coal group throughout the 

Danforth Hill coal fi eld (pl. 1, fi g. C).

The Goff coal group named after the Goff ranch (Hancock and Eby, 1930) averages 700 ft thick and consists of 

sandstone, mudstone, carbonaceous shale, and coal. The unit 

is separated from the Fairfi eld coal group below by approximately 1,000 ft of strata that are virtually barren of coal 

called the barren interval by Hancock and Eby (1930). Drill 

holes and outcrops in the Sulphur Creek syncline area contain 

coals assigned to the Goff coal group. The Lion Canyon coal 

group of Hancock and Eby (1930) averages 1,000 ft thick and 

directly overlies the Lion Canyon Sandstone (fi gs. 3 and 4) 

in the southwestern and western part of the Danforth Hills 

coal fi eld. The Lion Canyon coal group consists of sandstone, 

mudstones, carbonaceous shale, and thin lenticular coal beds. 

The barren interval and the Goff and Lion Canyon coal groups 

were not assessed in this study.

Coal Distribution in the Fairfi eld Coal Group

The Fairfi eld coal group was the only unit for which 

resources were assessed in this study. The coal group directly 

overlies the Trout Creek Sandstone and has average an maximum thicknesses of 1,130 ft and 1,770 ft, respectively, based 

on available drill-hole data. For this study, the Fairfi eld coal 

group was subdivided into seven coal zones in order to focus 

on the most important coal resources and resources were calculated for each coal zone. We were generally able to reliably 

identify and trace the individual zones across the area (fi g. C 

on pl. 1). 

The Fairfi eld coal group includes the FGA, FGB, FGC, 

FGD, FGE, FGF, and FGG coal zones (fi g. C on pl. 1 and fi g. 

4). The average thickness and average stratigraphic distance 

above the Trout Creek are shown for each zone in table 2. 

The range in the number of coal beds with net-coal thickness 

greater than 1.2 ft (Wood and others, 1983) is also shown. The 

Fairfi eld coal group contains at least 26 coal beds that have 

maximum thicknesses greater than 5 ft; 20 of these coal beds 

have a thicknesses greater than 12 ft. The deeper drill holes, 

which penetrated most of the Fairfi eld coal group, consistently 

contain total net-coal thicknesses greater than 100 ft. Total netcoal thickness greater than 200 ft occurs in a few of the deep 

drill holes that penetrated coals of the Fairfi eld, Goff, and Lion 

Canyon coal groups. The thickest net-coal deposits in the study 

area occur where there is a merging of several coal beds. The 

most signifi cant deposits of this type occur in the FGB and 

FGE zones, which locally have net-coal coal thicknesses of 

40 to 80 ft in intervals that have only minor partings. These 

intervals are known only from drill holes and have not been 

observed in outcrop.

The FGA coal zone of the Fairfi eld coal group (FGA coal 

zone, fi g. C, pl. 1) directly overlies the Trout Creek Sandstone 

Member of the Iles Formation; it ranges in thickness from 17 

to 280 ft and contains as many as fi ve coal beds. The FGA 

coal-thickness map (fi g. 6) displays the thickest total net coal 

(>30 ft) in townships T. 2 N., R. 93 W.; T. 4 N., Rs. 92 and 93 

W. The FGB zone ranges in thickness from 6 to 230 ft, with 

at least fi ve coal beds having a net-coal thickness of 20–30 ft 

over much of the area and 60 ft or more in T. 2 N., Rs. 92 

and 93 W. (fi g. 7). Zone FGC, 12 to 195 ft thick, contains as 

many as fi ve coal beds. The coal-thickness map (fi g. 8) shows 

net-coal thickness to range from 10 to 30 ft with the thickest (> 

M12 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
40 ft) occurring in the central part of the Danforth Hills (Tps. 

2 and 3 N., R. 93 W.). The FGD zone ranges in thickness 

from 3.5 to 248 ft and contains as many as four coal beds. 

Figure 9 shows a uniform distribution of total net-coal thickness ranging from 10 to 20 ft thick for this zone over most of 

the study area, and a maximum greater than 30 ft locally in the 

southeastern part. The FGE zone, 7.5 to 500 ft thick, contains 

at least nine coal beds with thicknesses generally ranging from 

10 to 50 ft, but exceeding 60 ft in several areas (fi g. 10). 

In the FGF zone, which ranges in thickness from 3 to 310 

ft, there are as many as seven coal beds with total net coal 

ranging in thickness from 10 to more than 40 ft (fi g. 11). This 

zone contains pods of coal greater than 30 ft thick in several 

townships (Tps. 2, 3, and 4 N., Rs. 93 and 94 W.). The FGG 

zone ranges in thickness from 2.5 to 410 ft and contains at 

least six coal beds. The coal-thickness map (fi g. 12) generally 

displays a uniform distribution of total net coal ranging in 

thickness from 5 to more than 20 ft. The variability in total netcoal thicknesses in the Fairfi eld coal group coal zones within 

the study area is due in part to the lenticularity and the varying 

number of beds within each coal zone.

Overburden-thickness maps (fi gs. 13–19) were 

constructed for each of the Fairfi eld coal zones based on 

depths where the elevation to the base of each zone was 

combined with the digital elevation data for the study 

area. Overburden is thickest along the southwest margin 

of the study area where the generally northwest-striking 

rocks of the Fairfi eld coal group dip from 30° to 50° to 

the southwest. Other areas of thick overburden are related 

to the Collom, Elkhorn, and Sulphur Creek synclines. The 

overburden thickness along the axis of the Sulphur Creek 

syncline is greater than 2,000 ft for the FGA through FGF 

zones, whereas the thinnest overburden areas are generally 

related to the crest of the Danforth Hills anticline and (or) 

near outcrops of the Trout Creek Sandstone. Only the FGE, 

FGF, and FGG zones in the north half of the study area have 

extensive areas where the overburden thickness is less than 

500 ft (fi gs. 17–19). This is the area where the Colowyo strip 

mine is located.

Net-coal-thickness category (Wood and others, 1983, p. 

34) maps (fi gs. 20–26) generally show net-coal-thickness 

trends that are in agreement with the coal isopach maps. The 

FGB, FGC, FGE, and FGF coal zones (fi gs. 21, 22, 24, 25, 

respectively) display the largest areas where total net-coal 

thickness exceeds 14 ft.

Coal Quality

Gale (1910) reported that coal analyses for several mines 

in the southern part of the Danforth Hills coal fi eld showed 

values for the heat of combustion to be 11,210 to 12,000 

Btu/lb, total sulfur content ranges to vary from 0.33 to 1.42 

percent, and ash yields to range from 5.2 to 5.52 percent 

on an as-received basis. Analytical data reported by Hancock 

(1925) for several mines in the northern part of the Danforth 

Hills shows heat of combustion to range from 10,140 to 

11,830 Btu/lb, total sulfur content to range from 0.3 to 1.12 

percent, and ash yields to range from 4.6 to 7.4 percent on 

an as-received basis. Coal quality data from Hancock and 

Eby (1930) for coals in several mines in the Meeker 15′

quadrangle, in the southwestern part of the Danforth Hills, 

suggest that the heat of combustion ranges from 10,790 

to 11,490 Btu/lb, total sulfur content ranges from 0.28 

to 1.36 percent, and ash yields range from 2.2 to 9.6 

percent on an as-received basis. The above analyses yield an 

apparent rank of high-volatile C bituminous using the Parr 

formula (American Society for Testing and Materials, 1997, 

D388-95). The Colowyo mine shipped about 4.6 million 

short tons of coal in 1994 with a with a mean heat of 

combustion of 10,550 Btu/lb, total sulfur content of 0.039 

percent, moisture content of 16.54 percent, and an ash-yield 

content of 5.32 percent (S.K. Allen, Colowyo Coal Company, 

written commun., 1996).

In the present study, the 47 coal samples from the 

Danforth Hills coal fi eld (table 3) were determined to be 

high-volatile C bituminous in apparent rank (Parr formula, 

American Society for Testing and Materials, 1997, D388-95) 

Table 2. Fairfield coal zones of the Williams Fork Formation showing, thickness range, average thickness, number of coal beds, 

general net-coal thickness range, maximum net-coal thickness, and average stratigraphic distance above the Trout Creek 

Sandstone Member of the Iles Formation, Mesaverde Group, Danforth Hills coal field. 

Fairfield 

coal zone 

Thickness range 

(feet) 

Average zone 

thickness 

(feet) 

Average stratigraphic 

distance above Trout Creek 

Sandstone Member (feet) 

Number of coal 

beds in zone 

General net-coal 

thickness range 

(feet) 

Maximum netcoal thickness 

(feet) 

FGG 2.5-410 160 970 1 to 6 5-20 >30 

FGF 3-310 210 760 1 to 7 10-40 >40 

FGE 7.5-500 280 480 1 to 9 10-50 >60 

FGD 3.5-248 120 360 1 to 4 10-20 >30 

FGC 12-195 115 240 1 to 5 10-30 >40 

FGB 6-230 110 130 1 to 5 20-30 >60 

FGA 17-280 130 0 1 to 5 10-20 >30 

Text continues on page 35

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M13
R. 96 W R. 95 W. R. 94 W.

R. 93 W. R. 92 W.

T. 5 N.

T. 4 N.

T. 3 N.

T. 2 N.

T. 1 N.

1 0 5 Miles

10

10

10

10

20

30

30

10

10

10

10

10

20

20

20 10

10

30

30

30

30 20 10

Colowyo coal

leases

PRLA

Moffat County

Rio Blanco County

Alluvial deposits (Quaternary),

Browns Park, Green River,

 Wasatch Fms. (Tertiary), and

Mancos Shale (Cretaceous)

Areal extent of the FGA zone

Colowyo Federal coal leases

and Preference Right Lease

Application (PRLA)

Net-coal thickness,

contour interval 10 feet

10

Map Explanation

County line

Township boundary

Fault - bar on

downthrown side

Iles and Williams Fork Fms.

and Mancos Shale

Figure 6. Map showing total net-coal thickness for the FGA coal zone of the Fairfi eld coal group of the Williams Fork Formation, Danforth Hills 

coal fi eld, Colorado. Outline of the Danforth Hills coal fi eld drawn on the base of the Upper Cretaceous Iles Formation. Areal extent of FGA zone 

shown in light green. Data not shown for the Colowyo Federal and State coal leases or PRLA.

M14 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Alluvial deposits (Quaternary),

Browns Park, Green River,

 Wasatch Fms. (Tertiary), and

Mancos Shale (Cretaceous)

Areal extent of the FGB zone

Colowyo Federal coal leases

and Preference Right Lease

Application (PRLA)

Net-coal thickness,

contour interval 10 feet

10

Map Explanation

County line

Township boundary

Fault - bar on

downthrown side

Iles and Williams Fork Fms.

and Mancos Shale

50

50

40

30 40

60

30

30

40 20

20

20

30

30

30

30

20

20

20

20

30

30 20

20

20

20

30 30

30

30

30

30

20

20

30

30

20

20

20

20

30

30

30

40

40

40

20 30

20

10

10

10

10

30

30

30

20

Colowyo coal

leases

R. 96 W. R. 95 W. R. 94 W.

R. 93 W. R. 92 W.

T. 5 N.

T. 4 N.

T. 3 N.

T. 2 N.

T. 1 N.

Moffat County

Rio Blanco County

1 0 5 Miles

Figure 7. Map showing total net-coal thickness for the FGB coal zone of the Fairfi eld coal group of the Williams Fork Formation, Danforth Hills 

coal fi eld, Colorado. Outline of the Danforth Hills coal fi eld drawn on the base of the Upper Cretaceous Iles Formation. Areal extent of FGB zone 

shown in light green. Data not shown for the Colowyo Federal and State coal leases or PRLA.

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M15
Alluvial deposits (Quaternary),

Browns Park, Green River,

 Wasatch Fms. (Tertiary), and

Mancos Shale (Cretaceous)

Areal extent of the FGC zone

Colowyo Federal coal leases

and Preference Right Lease

Application (PRLA)

Net-coal thickness,

contour interval 10 feet

10

Map Explanation

County line

Township boundary

Fault - bar on

downthrown side

Iles and Williams Fork Fms.

and Mancos Shale

1 0 5 Miles

20

20

20

10

10

30

30

10

30

20

30

30 30

40 30

20

20

40 20

30

30 30

20

40

40

40

40

40

50 20

20

30

10

10

20

20

20

10

10

10

20 20

30

30

20

10 10

10

R. 96 W. R. 95 W. R. 94 W.

T. 5 N.

R. 93 W. R. 92 W.

T. 4 N.

T. 3 N.

T. 2 N.

T. 1 N.

Moffat County

Rio Blanco County

Colowyo coal

leases

PRLA

Figure 8. Map showing total net-coal thickness for the FGC coal zone of the Fairfi eld coal group of the Williams Fork Formation, Danforth Hills 

coal fi eld, Colorado. Outline of the Danforth Hills coal fi eld drawn on the base of the Upper Cretaceous Iles Formation. Areal extent of FGC zone 

shown in light green. Data not shown for the Colowyo Federal and State coal leases or PRLA.

M16 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
20

20 30

30

20

20

20

10

10

10

20 20

30

10 10 10

10

10

10

10

20 10 20 30

10

10

10

30 20

20

20

10

10

10

10

20

20

30

20

10

10 10

15

10

10

10

10

10

1 0 5 Miles

Alluvial deposits (Quaternary),

Browns Park, Green River,

 Wasatch Fms. (Tertiary), and

Mancos Shale (Cretaceous)

Areal extent of the FGD zone

Colowyo Federal coal leases

and Preference Right Lease

Application (PRLA)

Net-coal thickness,

contour interval 10 feet

10

Map Explanation

County line

Township boundary

Fault - bar on

downthrown side

Iles and Williams Fork Fms.

and Mancos Shale

Colowyo coal

leases

PRLA

R. 96 W. R. 95 W. R. 94 W.

T. 5 N.

R. 93 W. R. 92 W.

T. 4 N.

T. 3 N.

T. 2 N.

T. 1 N.

Moffat County

Rio Blanco

County

Figure 9. Map showing total net-coal thickness for the FGD coal zone of the Fairfi eld coal group of the Williams Fork Formation, Danforth Hills 

coal fi eld, Colorado. Outline of the Danforth Hills coal fi eld drawn on the base of the Upper Cretaceous Iles Formation. Areal extent of FGD zone 

shown in light green. Data not shown for the Colowyo Federal and State coal leases or PRLA.

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M17
20

20 30

40

50

60

30

30

40

30

30

4040 50 40

30

20

30

30

30

30

30

40

50

20

20

10 40 50 10

30

30

20

10

20

20

20

50

50

40

20

20 20

60

40

40

40

40

40

40 50

50

10

10

10

10

10

60

10

30 30

10

50

50

40

40

30

30

20

20

20

40

50

10 50 20

50

40 30

30

40

50

60 10 60

60

20

30

50 40

50

60

60

30

50

20

50

50

50

10

60 40

60

20 20 10

30 30 40

1 0 5 Miles

Alluvial deposits (Quaternary),

Browns Park, Green River,

 Wasatch Fms. (Tertiary), and

Mancos Shale (Cretaceous)

Areal extent of the FGE zone

Colowyo Federal coal leases

and Preference Right Lease

Application (PRLA)

Net-coal thickness,

contour interval 10 feet

10

Map Explanation

County line

Township boundary

Fault - bar on

downthrown side

Iles and Williams Fork Fms.

and Mancos Shale

Moffat County

Rio Blanco

County

Colowyo coal

leases

PRLA

R. 96 W. R. 95 W. R. 94 W.

T. 5 N.

R. 93 W. R. 92 W.

T. 4 N.

T. 3 N.

T. 2 N.

T. 1 N.

Figure 10. Map showing total net-coal thickness for the FGE coal zone of the Fairfi eld coal group of the Williams Fork Formation, Danforth Hills 

coal fi eld, Colorado. Outline of the Danforth Hills coal fi eld drawn on the base of the Upper Cretaceous Iles Formation. Areal extent of FGE zone 

shown in light green. Data not shown for the Colowyo Federal and State coal leases or PRLA.

M18 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
30

40

40

20

10

20 20

30 3040

20

20

10 10

10

10

20

20

20

20

10

10

10 10

30

30

10

10

10

30

30

10

10 30 30

10

10

30

10

20 20

20

40

30 30

20

20

20

20

20

30

30

20 30

20

20

20

20

20

30

Moffat County

Rio Blanco County

1 0 5 Miles

Alluvial deposits (Quaternary),

Browns Park, Green River,

 Wasatch Fms. (Tertiary), and

Mancos Shale (Cretaceous)

Areal extent of the FGF zone

Colowyo Federal coal leases

and Preference Right Lease

Application (PRLA)

Net-coal thickness,

contour interval 10 feet

10

Map Explanation

County line

Township boundary

Fault - bar on

downthrown side

Iles and Williams Fork Fms.

and Mancos Shale

T. 2 N.

T. 1 N.

R. 96 W. R. 95 W. R. 94 W.

T. 5 N.

R. 93 W. R. 92 W.

T. 4 N.

T. 3 N.

Colowyo coal

leases

PRLA

Figure 11. Map showing total net-coal thickness for the FGF coal zone of the Fairfi eld coal group of the Williams Fork Formation, Danforth Hills 

coal fi eld, Colorado. Outline of the Danforth Hills coal fi eld drawn on the base of the Upper Cretaceous Iles Formation. Areal extent of FGF zone 

shown in light green. Data not shown for the Colowyo Federal and State coal leases or PRLA.

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M19
10

10

10 10

10

10

10

20

20

10 10

20 20

20

10

10

10

10 10

20

10

10 10

10

10 10

10

10

10

20 10

Colowyo coal

leases

PRLA

Moffat County

Rio Blanco County

1 0 5 Miles

Alluvial deposits (Quaternary),

Browns Park, Green River,

 Wasatch Fms. (Tertiary), and

Mancos Shale (Cretaceous)

Areal extent of the FGG zone

Colowyo Federal coal leases

and Preference Right Lease

Application (PRLA)

Net-coal thickness,

contour interval 10 feet

10

Map Explanation

County line

Township boundary

Fault - bar on

downthrown side

Iles and Williams Fork Fms.

and Mancos Shale

R. 96 W. R. 95 W. R. 94 W.

T. 5 N.

R. 93 W. R. 92 W.

T. 4 N.

T. 2 N.

T. 1 N.

T. 3 N.

Figure 12. Map showing total net-coal thickness for the FGG coal zone of the Fairfi eld coal group of the Williams Fork Formation, Danforth Hills 

coal fi eld, Colorado. Outline of the Danforth Hills coal fi eld drawn on the base of the Upper Cretaceous Iles Formation. Areal extent of FGG zone 

shown in light green. Data not shown for the Colowyo Federal and State coal leases or PRLA.

M20 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
1 0 5 Miles

Alluvial deposits (Quaternary),

Browns Park, Green River,

 Wasatch Fms. (Tertiary), and

Mancos Shale (Cretaceous)

Iles and Williams Fork Fms.

and Mancos Shale

Undivided Quaternary, Tertiary,

Cretaceous

Upper Cretaceous

Map Explanation

Fault - bar on

downthrown side

0-500

500-1000

1000-2000

2000-3000

3000-6000

Overburden categories (in feet)

R. 96 W R. 95 W. R. 94 W.

R. 93 W. R. 92 W.

T. 5 N.

T. 4 N.

T. 3 N.

T. 2 N.

T. 1 N.

Figure 13. Map showing overburden thickness for the FGA coal zone of the Fairfi eld coal group of the Williams Fork Formation, Danforth Hills 

coal fi eld, Colorado. Outline of the Danforth Hills coal fi eld drawn on the base of the Upper Cretaceous Iles Formation. Areal extent of FGA 

zone is drawn on the top of the Trout Creek Sandstone.

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M21
1 0 5 Miles

Alluvial deposits (Quaternary),

Browns Park, Green River,

 Wasatch Fms. (Tertiary), and

Mancos Shale (Cretaceous)

Iles and Williams Fork Fms.

and Mancos Shale

Undivided Quaternary, Tertiary,

Cretaceous

Upper Cretaceous

Map Explanation

Fault - bar on

downthrown side

0-500

500-1000

1000-2000

2000-3000

3000-6000

Overburden categories (in feet)

R. 96 W. R. 95 W. R. 94 W.

R. 93 W. R. 92 W.

T. 5 N.

T. 4 N.

T. 3 N.

T. 2 N.

T. 1 N.

Figure 14. Map showing overburden thickness for the FGB coal zone of the Fairfi eld coal group of the Williams Fork Formation, Danforth Hills 

coal fi eld, Colorado. Outline of the Danforth Hills coal fi eld drawn on the base of the Upper Cretaceous Iles Formation. Areal extent of FGB 

zone is drawn on the top of the Trout Creek Sandstone. 

M22 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
1 0 5 Miles

Alluvial deposits (Quaternary),

Browns Park, Green River,

 Wasatch Fms. (Tertiary), and

Mancos Shale (Cretaceous)

Iles and Williams Fork Fms.

and Mancos Shale

Undivided Quaternary, Tertiary,

Cretaceous

Upper Cretaceous

Map Explanation

Fault - bar on

downthrown side

0-500

500-1000

1000-2000

2000-3000

3000-6000

Overburden categories (in feet)

R. 96 W. R. 95 W. R. 94 W.

T. 5 N.

R. 93 W. R. 92 W.

T. 4 N.

T. 3 N.

T. 2 N.

T. 1 N.

Figure 15. Map showing overburden thickness for the FGC coal zone of the Fairfi eld coal group of the Williams Fork Formation, Danforth 

Hills coal fi eld, Colorado. Outline of the Danforth Hills coal fi eld drawn on the base of the Upper Cretaceous Iles Formation. Areal extent of 

FGC drawn on base of zone.

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M23
1 0 5 Miles

Alluvial deposits (Quaternary),

Browns Park, Green River,

 Wasatch Fms. (Tertiary), and

Mancos Shale (Cretaceous)

Iles and Williams Fork Fms.

and Mancos Shale

Undivided Quaternary, Tertiary,

Cretaceous

Upper Cretaceous

Map Explanation

Fault - bar on

downthrown side

0-500

500-1000

1000-2000

2000-3000

3000-6000

Overburden categories (in feet)

R. 96 W. R. 95 W. R. 94 W.

T. 5 N.

R. 93 W. R. 92 W.

T. 4 N.

T. 3 N.

T. 2 N.

T. 1 N.

Figure 16. Map showing overburden thickness for the FGD coal zone of the Fairfi eld coal group of the Williams Fork Formation, Danforth 

Hills coal fi eld, Colorado. Outline of the Danforth Hills coal fi eld drawn on the base of the Upper Cretaceous Iles Formation. Areal extent of 

FGD drawn on base of zone. 

M24 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Alluvial deposits (Quaternary),

Browns Park, Green River,

 Wasatch Fms. (Tertiary), and

Mancos Shale (Cretaceous)

Iles and Williams Fork Fms.

and Mancos Shale

Undivided Quaternary, Tertiary,

Cretaceous

Upper Cretaceous

Map Explanation

Fault - bar on

downthrown side

0-500

500-1000

1000-2000

2000-3000

3000-6000

Overburden categories (in feet)

1 0 5 Miles

R. 96 W. R. 95 W. R. 94 W.

T. 5 N.

R. 93 W. R. 92 W.

T. 4 N.

T. 3 N.

T. 2 N.

T. 1 N.

Figure 17. Map showing overburden thickness for the FGE coal zone of the Fairfi eld coal group of the Williams Fork Formation, Danforth Hills 

coal fi eld, Colorado. Outline of the Danforth Hills coal fi eld drawn on the base of the Upper Cretaceous Iles Formation. Areal extent of FGE drawn 

on base of zone. Data not shown for the Colowyo Federal and State coal leases or PRLA.

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M25
T. 2 N.

T. 1 N.

R. 96 W. R. 95 W. R. 94 W.

T. 5 N.

R. 93 W. R. 92 W.

T. 4 N.

Alluvial deposits (Quaternary), T. 3 N.

Browns Park, Green River,

 Wasatch Fms. (Tertiary), and

Mancos Shale (Cretaceous)

Iles and Williams Fork Fms.

and Mancos Shale

Undivided Quaternary, Tertiary,

Cretaceous

Upper Cretaceous

Map Explanation

Fault - bar on

downthrown side

0-500

500-1000

1000-2000

2000-3000

3000-6000

Overburden categories (in feet)

1 0 5 Miles

Figure 18. Map showing overburden thickness for the FGF coal zone of the Fairfi eld coal group of the Williams Fork Formation, Danforth 

Hills coal fi eld, Colorado. Outline of the Danforth Hills coal fi eld drawn on the base of the Upper Cretaceous Iles Formation. Areal extent of 

FGF drawn on base of zone. 

M26 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
R. 96 W. R. 95 W. R. 94 W.

T. 5 N.

R. 93 W. R. 92 W.

T. 4 N.

T. 2 N.

T. 1 N.

Alluvial deposits (Quaternary), T. 3 N.

Browns Park, Green River,

 Wasatch Fms. (Tertiary), and

Mancos Shale (Cretaceous)

Iles and Williams Fork Fms.

and Mancos Shale

Undivided Quaternary, Tertiary,

Cretaceous

Upper Cretaceous

Map Explanation

Fault - bar on

downthrown side

0-500

500-1000

1000-2000

2000-3000

3000-6000

Overburden categories (in feet)

1 0 5 Miles

Figure 19. Map showing overburden thickness for the FGG coal zone of the Fairfi eld coal group of the Williams Fork Formation, Danforth 

Hills coal fi eld, Colorado. Outline of the Danforth Hills coal fi eld drawn on the base of the Upper Cretaceous Iles Formation. Areal extent of 

FGG drawn on base of zone. 

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M27
Colowyo coal

leases

PRLA

R. 96 W R. 95 W. R. 94 W.

R. 93 W. R. 92 W.

T. 5 N.

T. 4 N.

T. 3 N.

T. 2 N.

T. 1 N.

1 0 5 Miles

Colowyo Federal coal leases

and Preference Right Lease

Application (PRLA)

2.3-3.5

3.5-7.0

7.0-14.0

>14.0

Coal-thickness categories (in feet)

Township boundary

Fault - bar on

downthrown side

Alluvial deposits (Quaternary),

Browns Park, Green River,

Wasatch Fms. (Tertiary), and

Mancos Shale (Cretaceous)

Iles and Williams Fork Fms.

and Mancos Shale

Map Explanation

Figure 20. Map showing coal-thickness categories for the FGA coal zone of the Fairfi eld coal group of the Williams Fork Formation, Danforth 

Hills coal fi eld, Colorado. Outline of the Danforth Hills coal fi eld drawn on the base of the Upper Cretaceous Iles Formation. Areal extent of FGA 

drawn on base of zone. Data not shown for the Colowyo Federal and State coal leases or PRLA.

M28 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Colowyo coal

leases

PRLA

R. 96 W. R. 95 W. R. 94 W.

R. 93 W. R. 92 W.

T. 5 N.

T. 4 N.

T. 3 N.

T. 2 N.

T. 1 N.

1 0 5 Miles

Colowyo Federal coal leases

and Preference Right Lease

Application (PRLA)

3.5-7.0

7.0-14.0

>14.0

Coal-thickness categories (in feet)

Township boundary

Fault - bar on

downthrown side

Alluvial deposits (Quaternary),

Browns Park, Green River,

Wasatch Fms. (Tertiary), and

Mancos Shale (Cretaceous)

Iles and Williams Fork Fms.

and Mancos Shale

Map Explanation

Figure 21. Map showing coal-thickness categories for the FGB coal zone of the Fairfi eld coal group of the Williams Fork Formation, Danforth 

Hills coal fi eld, Colorado. Outline of the Danforth Hills coal fi eld drawn on the base of the Upper Cretaceous Iles Formation. Areal extent of FGB 

drawn on base of zone. Data not shown for the Colowyo Federal and State coal leases or PRLA.

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M29
Colowyo coal

leases

PRLA

R. 96 W. R. 95 W. R. 94 W.

T. 5 N.

R. 93 W. R. 92 W.

T. 4 N.

T. 3 N.

T. 2 N.

T. 1 N.

Colowyo Federal coal leases

and Preference Right Lease

Application (PRLA)

2.3-3.5

3.5-7.0

7.0-14.0

>14.0

Coal-thickness categories (in feet)

Township boundary

Fault - bar on

downthrown side

Alluvial deposits (Quaternary),

Browns Park, Green River,

Wasatch Fms. (Tertiary), and

Mancos Shale (Cretaceous)

Iles and Williams Fork Fms.

and Mancos Shale

Map Explanation

1 0 5 Miles

Figure 22. Map showing coal-thickness categories for the FGC coal zone of the Fairfi eld coal group of the Williams Fork Formation, Danforth 

Hills coal fi eld, Colorado. Outline of the Danforth Hills coal fi eld drawn on the base of the Upper Cretaceous Iles Formation. Areal extent of FGC 

drawn on base of zone. Data not shown for the Colowyo Federal and State coal leases or PRLA.

M30 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Colowyo coal

leases

PRLA

R. 96 W. R. 95 W. R. 94 W.

T. 5 N.

R. 93 W. R. 92 W.

T. 4 N.

T. 3 N.

T. 2 N.

T. 1 N.

1 0 5 Miles

Colowyo Federal coal leases

and Preference Right Lease

Application (PRLA)

2.3-3.5

3.5-7.0

7.0-14.0

>14.0

Coal-thickness categories (in feet)

Township boundary

Fault - bar on

downthrown side

Alluvial deposits (Quaternary),

Browns Park, Green River,

Wasatch Fms. (Tertiary), and

Mancos Shale (Cretaceous)

Iles and Williams Fork Fms.

and Mancos Shale

Map Explanation

Figure 23. Map showing coal-thickness categories for the FGD coal zone of the Fairfi eld coal group of the Williams Fork Formation, Danforth 

Hills coal fi eld, Colorado. Outline of the Danforth Hills coal fi eld drawn on the base of the Upper Cretaceous Iles Formation. Areal extent of FGD 

drawn on base of zone. Data not shown for the Colowyo Federal and State coal leases or PRLA.

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M31
Colowyo coal

leases

PRLA

R. 96 W. R. 95 W. R. 94 W.

T. 5 N.

R. 93 W. R. 92 W.

T. 4 N.

T. 3 N.

T. 2 N.

T. 1 N.

Colowyo Federal coal leases

and Preference Right Lease

Application (PRLA)

2.3-3.5

3.5-7.0

7.0-14.0

>14.0

Coal-thickness categories (in feet)

Township boundary

Fault - bar on

downthrown side

Alluvial deposits (Quaternary),

Browns Park, Green River,

Wasatch Fms. (Tertiary), and

Mancos Shale (Cretaceous)

Iles and Williams Fork Fms.

and Mancos Shale

Map Explanation

1 0 5 Miles

Figure 24. Map showing coal-thickness categories for the FGE coal zone of the Fairfi eld coal group of the Williams Fork Formation, Danforth 

Hills coal fi eld, Colorado. Outline of the Danforth Hills coal fi eld drawn on the base of the Upper Cretaceous Iles Formation. Areal extent of FGE 

drawn on base of zone. Data not shown for the Colowyo Federal and State coal leases or PRLA.

M32 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Colowyo coal

leases

PRLA

T. 2 N.

T. 1 N.

R. 96 W. R. 95 W. R. 94 W.

T. 5 N.

R. 93 W. R. 92 W.

T. 4 N.

T. 3 N.

1 0 5 Miles

Colowyo Federal coal leases

and Preference Right Lease

Application (PRLA)

2.3-3.5

3.5-7.0

7.0-14.0

>14.0

Coal-thickness categories (in feet)

Township boundary

Fault - bar on

downthrown side

Alluvial deposits (Quaternary),

Browns Park, Green River,

Wasatch Fms. (Tertiary), and

Mancos Shale (Cretaceous)

Iles and Williams Fork Fms.

and Mancos Shale

Map Explanation

1.2-2.3

Figure 25. Map showing coal-thickness categories for the FGF coal zone of the Fairfi eld coal group of the Williams Fork Formation, Danforth 

Hills coal fi eld, Colorado. Outline of the Danforth Hills coal fi eld drawn on the base of the Upper Cretaceous Iles Formation. Areal extent of FGF 

drawn on base of zone. Data not shown for the Colowyo Federal and State coal leases or PRLA.

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M33
Colowyo coal

leases

PRLA

R. 96 W. R. 95 W. R. 94 W.

T. 5 N.

R. 93 W. R. 92 W.

T. 4 N.

T. 2 N.

T. 1 N.

T. 3 N.

1 0 5 Miles

Colowyo Federal coal leases

and Preference Right Lease

Application (PRLA)

2.3-3.5

3.5-7.0

7.0-14.0

>14.0

Coal-thickness categories (in feet)

Township boundary

Fault - bar on

downthrown side

Alluvial deposits (Quaternary),

Browns Park, Green River,

Wasatch Fms. (Tertiary), and

Mancos Shale (Cretaceous)

Iles and Williams Fork Fms.

and Mancos Shale

Map Explanation

1.2-2.3

Figure 26. Map showing coal-thickness categories for the FGG coal zone of the Fairfi eld coal group of the Williams Fork Formation, Danforth 

Hills coal fi eld, Colorado. Outline of the Danforth Hills coal fi eld drawn on the base of the Upper Cretaceous Iles Formation. Areal extent of FGG 

drawn on base of zone. Data not shown for the Colowyo Federal and State coal leases or PRLA.

M34 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
with a calculated mean heat of combustion (moist, mineralmatter-free basis) of 11,030 Btu/lb. Hildebrand and others 

(1981) reported proximate and ultimate data on 19 coal samples 

included in table 3. Nine samples were collected at the Colowyo 

mine, and the other samples were from drill cores within the 

Fairfi eld coal group elsewhere in the study area. The coal has 

a mean heat of combustion of 9,650 Btu/lb, a total sulfur 

content of 0.47 percent, and an ash yield of 11.51 percent on 

an as-received basis (R.H. Affolter, written commun., 1998). 

Ranges in values for proximate and ultimate analyses are given 

in table 3. Means and ranges of selected trace-element data for 

as many as 50 coal samples from the Danforth Hills and the 

Fairfi eld group are given in table 4. The methods for sampling 

and inorganic analysis of coal used to determine the elements 

listed in table 4 are discussed in Golightly and Simon (1989).

Methodology

Digital fi les or coverages of various geologic and other 

features such as outcrop lines, elevation data, coal thickness, 

faults, fold axes, Federal coal leases, and mined-out areas were 

created within the study area. The coal benches and parting 

thicknesses were determined from geophysical logs using the 

natural gamma and density traces. Coal-bed thicknesses from 

the log traces are calculated using a USGS program (G.D. 

Stricker, written commun., 1998) that follows the methodology 

of Wood and others (1983) and excludes bituminous coal beds 

less than 1.2 ft thick. The total net-coal thickness values for 

each zone were used in the resource calculations (see Roberts 

and others, chap. C, this CD-ROM).

Coal resources for the Fairfi eld coal group are reported in 

the identifi ed and hypothetical resource categories (Wood and 

others, 1979). Identifi ed resources are located within a 3-mile 

radius of a data point and include the reliability categories 

of measured, indicated, and inferred. The measured resource 

category has the highest degree of geologic assurance and is 

located within a 0.25-mile radius of a data point. The indicated 

resource category has a more moderate degree of geologic 

assurance and is located within an area bounded by a 0.25- 

to 0.75-mile radius from a data point. The inferred resource 

category has a lower degree of geologic assurance and is 

located within an area bounded by a 0.75- to 3-mile radius 

from a data point. The hypothetical resource category has the 

lowest degree of geologic assurance in this scheme and is 

located within an area beyond a 3-mile radius from a data 

point and to a depth of 6,000 ft. Coal resources estimated 

in this study do not include the area inside the Colowyo 

Federal and State coal leases and the Preference Right Lease 

Table 3. Number of samples, range, arithmetic mean, and standard deviation of proximate and ultimate analyses, heat 

of combustion, forms of sulfur, and ash-fusion temperatures of coal from the Danforth Hills coal field. 

[All values are in percent except Btu/lb and ash-fusion temperatures, and are reported on the as-received basis (R.H. Affolter, written 

commun, 1998)] 

 Number of Range Arithmetic Standard 

 samples Minimum Maximum mean deviation 

Proximate and ultimate analyses 

Moisture 47 2.9 23.8 14.82 3.27 

Volatile matter 47 11.3 34.9 30.86 4.11 

Fixed carbon 47 22.5 50.9 42.82 6.23 

Ash 47 2.59 45.8 11.51 10.29 

Hydrogen 47 2.5 6.16 5.48 0.65 

Carbon 47 33.5 64.4 55.85 7.53 

Nitrogen 47 0.6 1.62 1.31 0.24 

Oxygen 47 6.4 30.6 25.37 3.72 

Sulfur 47 0.3 1.1 0.47 0.20 

Heat of combustion 

Btu/lb 47 5,780 11,200 9,650 1,320 

Forms of sulfur 

Sulfate 41 0.01 0.04 0.01 0.01 

Pyritic 47 0.01 0.41 0.09 0.10 

Organic 47 0.12 0.76 0.37 0.13 

Ash-fusion temperatures,  ̊ F 

Initial deformation 47 2,030 2,910 2,420 220 

Softening temperature 47 2,090 2,910 2,520 220 

Fluid temperature 47 2,140 2,910 2,590 210 

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M35
Application (PRLA). Estimated coal resource tonnages were 

rounded to 2 signifi cant fi gures. Therefore, totals may not 

equal the sum of individual categories because of independent 

rounding.

Estimates of coal resource tonnages for the Fairfi eld coal 

group are based on the methodology of Wood and others 

(1983) which uses a mean density of 1.32 g/cm3 or 1,800 

short tons/acre-ft for bituminous coal. Also, following this 

methodology (1) calculations were made for the 0–500 ft, 

500–1,000 ft, 1,000–2,000 ft, 2,000–3,000 ft, and 3,000–6,000 

ft overburden categories by integrating the overburden maps 

(fi gs. 13–19), net coal isopach maps (fi gs. 6–12), and the areal 

extent of each zone (fi gs. 6–12) and (2) isopach maps that 

show total net coal in the thickness categories of 1.2–2.3, 

2.3–3.5, 3.5–7.0, 7.0–14.0, and greater than 14.0 ft were conText continues on page 52

Table 4. Number of samples, range, arithmetic mean, and standard deviation of ash content and 36 elements in coal 

from the Fairfield coal group of the Williams Fork Formaiton, Danforth Hills coal field, Colorado Plateau. 

[All analyses are in percent or parts per million and are reported on a whole-coal basis. L, less than value shown] 

 Number of Range Arithmetic Standard 

 samples Minimum Maximum mean deviation 

Percent 

Ash 50 2.4 45 13 11 

Si 49 0.32 15 3.3 3.6 

Al 49 0.18 4.2 1.3 0.96 

Ca 49 0.16 2.2 0.49 0.35 

Mg 50 0.009 0.36 0.1 0.068 

Na 50 0.003 1.1 0.078 0.15 

K 49 0.002 0.65 0.12 0.16 

Fe 49 0.084 1 0.31 0.24 

Ti 49 0.009 0.2 0.058 0.045 

Parts per million 

As 50 0.35 11 1.5 1.9 

B 50 21 83 48 15 

Ba 50 81 940 240 170 

Be 46 0.14L 4.4 1.2 1 

Co 50 0.33 8.8 2.3 1.8 

Cr 48 0.1L 47 7.5 8.7 

Cu 50 1.3 33 6.4 5.9 

F 50 20L 510 120 100 

Ga 50 0.62 14 3.2 2.9 

Hg 50 0.010L 0.39 0.046 0.071 

La 44 4.3L 22 6.8 5.3 

Li 50 0.28 63 6.5 10 

Mn 50 0.81 150 21 31 

Mo 46 0.071L 3.1 0.68 0.65 

Nb 47 0.68L 13 2.2 2.8 

Ni 50 0.86 33 7 7.3 

Pb 50 0.72L 57 4.8 8.6 

Sb 50 0.10L 4.4 0.77 0.85 

Sc 50 0.77L 8.8 1.8 1.6 

Se 44 0.25 1.9 0.71 0.31 

Sr 50 11 520 120 110 

Th 50 0.3 10 2.4 1.8 

U 50 0.18L 6.3 1.4 1.2 

V 50 2.1 88 15 16 

Y 50 1 22 5.9 5.1 

Yb 50 0.1 2.2 0.53 0.45 

Zn 50 1.2 100 15 21 

Zr 50 2.4 110 28 25 

M36 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Table 5. Identified and hypothetical coal resources in millions of short tons for the FGA zone of the Fairfield coal group, 

Williams Fork Formation, Danforth Hills coal field reported by quadrangle, township, and ownership categories. 

[Resources are not reported for areas inside the Colowyo Federal coal leases and Preference Right Lease Application (PRLA) 

boundaries. Coal resources rounded to two significant figures] 

 Overburden categories (feet) Grand total 

 0-500 500-1,000 1,000-2,000 2,000-3,000 3,000-6,000 

By quadrangle 

AXIAL 47 55 48 0 0 150 

DEVILS HOLE GULCH 190 100 56 32 100 480 

EASTON GULCH 160 160 230 0 0 560 

MEEKER 14 13 46 23 28 120 

MONUMENT BUTTE 9.8 27 18 0 0 54 

NINEMILE GAP 48 140 160 67 0 410 

PRICE CREEK 15 0.07 0 0 0 15 

RATTLESNAKE MESA 58 38 120 11 0 230 

SAWMILL MOUNTAIN 4.2 0 0 0 0 4.2 

THORNBURGH 32 25 15 0 0 72 

WHITE ROCK 16 35 58 33 120 260 

Total 590 600 750 170 250 2400 

 

By township 

T1N R93W 0.63 0 0 0 0 0.63 

T1N R94W 4.4 2.9 0.72 0 0 8.1 

T2N R92W 26 9.5 0.96 0 0 36 

T2N R93W 66 80 190 78 0 410 

T2N R94W 51 30 88 51 110 330 

T2N R95W 0 0 0.27 3.1 38 41 

T3N R92W 34 45 63 0 0 140 

T3N R93W 23 82 87 0 0 190 

T3N R94W 140 100 35 0 0 280 

T3N R95W 59 46 63 34 100 300 

T4N R92W 12 25 1.1 0 0 37 

T4N R93W 42 49 19 0 0 110 

T4N R94W 110 130 200 0 0 440 

T4N R95W 28 0 0 0 0 28 

T5N R94W 0.45 0 0 0 0 0.45 

Grand total 590 600 750 170 250 2400 

Coal ownership Total Surface ownership Total 

Federal 2100 BLM 640 

Non-Federal 300 Private 1700 

 State 83 

Total 2400 2400 

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M37
Table 6. Identified and hypothetical coal resources in millions of short tons for the FGA zone of the Fairfield coal group, Williams Fork Formation, Danforth Hills 

reliability, overburden, and coal-thickness categories. 

[Resources are not reported for area inside the Colowyo Federal coal leases and Preference Right Lease Application (PRLA) boundaries. Coal resources rounded to two significan

County Reliability 0-500 feet overburden 

coal-thickness categories, in feet 

0-500 

total 

500-1000 feet overburden 

coal-thickness categories, in feet 

 2.3-3.5 3.5-7.0 7.0-14.0 >14.0 2.3-3.5 3.5-7.0 7.0-14.0 

Moffat Identified 0 4.1 110 190 300 0 8.2 150  Hypothetical 0 0.85 14 7.3 22 0 0 24 Moffat total 0 4.9 120 200 330 0 8.2 170 Rio Blanco Identified 2.6 32 130 75 240 1.5 47 120  Hypothetical 0 1.8 15 4.0 21 0 .30 11 Rio Blanco total 2.6 33 150 79 260 1.5 47 130 Total 2.6 38 270 280 590 1.5 55 300 

County Reliability 1,000-2,000 feet overburden 

coal-thickness categories, in feet 

1,000-2,000 

total 

2,000-3,000 feet overburden 

coal-thickness categories, in feet 

 2.3-3.5 3.5-7.0 7.0-14.0 >14.0 3.5-7.0 7.0-14.0 >14.0 

Moffat Identified 0 0.8 170 190 360 0 0 11  Hypothetical 0 0 19 0 19 0 0 0 Moffat total 0 0.8 190 190 380 0 0 11 Rio Blanco Identified 0.33 11 140 180 330 0.22 67 62  Hypothetical 0 0 19 12 31 0 23 2.1 Rio Blanco total 0.33 11 160 190 360 0.22 90 64 Total 0.33 12 350 390 740 0.22 90 75 

County Reliability 3,000-6,000 feet overburden 

coal-thickness categories, in feet 

3,000-6,000 

total 

Grand 

total 

 7.0-14.0 >14.0 

Moffat Identified 0 19 19 1000  Hypothetical 0 6.1 6.1 900 Moffat total 0 25 25 1100 Rio Blanco Identified 5.4 44 49 980  Hypothetical 110 66 180 270 Rio Blanco total 120 110 230 1300 Total 120 135 250 2400 
Table 7. Identified and hypothetical coal resources in millions of short tons for the FGB zone of the Fairfield coal 

group, Williams Fork Formation, Danforth Hills coal field. 

[Resources are reported in overburden categories and are grouped by county, township, and 71⁄2-minute quadrangle. Resources in 

coal- and surface-ownership categories are also reported. Resources are not reported for areas inside the Colowyo Federal coal 

leases and Preference Right Lease Application (PRLA) boundaries. Coal resources rounded to two significant figures] 

 Overburden categories (feet) Grand total 

 0-500 500-1,000 1,000-2,000 2,000-3,000 3,000-6,000 

By quadrangle 

AXIAL 29 45 63 0 0 140 

DEVILS HOLE GULCH 440 240 120 68 230 1100 

EASTON GULCH 210 270 410 0 0 890 

MEEKER 28 27 98 52 71 280 

MONUMENT BUTTE 6.7 18 19 0 0 43 

NINEMILE GAP 230 480 340 170 0 1200 

PRICE CREEK 22 0.09 0 0 0 22 

RATTLESNAKE MESA 110 62 220 22 0 420 

SAWMILL MOUNTAIN 16 0 0 0 0 16 

THORNBURGH 87 45 22 0 0 150 

WHITE ROCK 26 60 92 53 190 420 

Grand total 1200 1200 1400 370 490 4700 

By township 

T1N R93W 0.67 0 0 0 0 0.67 

T1N R94W 10 7.0 1.8 0 0 19 

T2N R92W 140 75 8.4 0 0 220 

T2N R93W 150 220 400 190 0 950 

T2N R94W 99 60 180 120 270 730 

T2N R95W 0 0 0.54 6.1 70 80 

T3N R92W 78 76 82 0 0 240 

T3N R93W 97 240 160 0 0 490 

T3N R94W 350 280 77 0 0 700 

T3N R95W 100 81 100 53 150 480 

T4N R92W 5.6 14 0.89 0 0 20 

T4N R93W 27 37 26 0 0 90 

T4N R94W 130 165 340 0 0 630 

T4N R95W 39 0 0 0 0 39 

T5N R94W 0.32 0 0 0 0 0.32 

Grand total 1200 1200 1400 370 490 4700 

By ownership category 

Coal ownership Total Surface ownership Total 

Federal 4100 BLM 1200 

Non-Federal 600 Private 3400 

 State 120 

Total 4700 4700 

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M39
Table 8. Identified and hypothetical coal resources in millions of short tons for the FGB zone of the Fairfield coal group, Williams Fork Formation, Danforth Hills 

reliability, overburden, and coal-thickness categories. 

[Resources are not reported for areas inside Colowyo Federal coal leases and Preference Right Lease Application (PRLA) boundaries. Coal resources rounded to two significant f

 0-500 feet overburden 

coal-thickness categories, in feet 

0-500 total 500-1000 feet overburden 

coal-thickness categories, in feet 

500-

County Reliability 3.5-7.0 7.0-14.0 >14.0 3.5-7.0 7.0-14.0 >14.0 

Moffat Identified 3.9 17 460 480 1.4 32 520 5 Hypothetical 1.8 4.8 17 24 2.6 14 8.0 Moffat total 5.7 22 480 500 4.0 46 530 5Rio Blanco Identified 0 1.4 670 700 0 20 630 6 Hypothetical 0 0 15 15 0 0 17 Rio Blanco total 0 1.4 720 720 0 20 650 6Grand total 5.7 23 1200 1200 4.0 66 1200 12

County Reliability 1,000-2000 feet overburden 

coal-thickness categories (feet) 

1,000-2,000 

total 

2000-3,000 feet overburden 

coal-thickness categories (feet) 

2,000-3,000 

total 

3,000-6,000 feet overburden 

coal-thickness categories (feet

 7.0-14.0 >14.0 >14.0 >14.0 

Moffat Identified 38 580 610 15 15 24  Hypothetical 5.6 0.63 6.3 0 0 7.3 Moffat total 44 580 620 15 15 31 Rio Blanco Identified 33 680 710 310 310 150  Hypothetical 0 41 41 39 39 310 Rio Blanco total 33 720 750 350 350 460 Grand total 77 1300 1400 370 370 490 
Table 9. Identified and hypothetical coal resources in millions of short tons for the FGC zone of the Fairfield coal 

group, Williams Fork Formation, Danforth Hills coal field. 

[Resources are grouped in overburden categories and are grouped by county, township, and 71⁄2-minute quadrangle. Resources 

in coal- and surface-ownership categories are also reported. Resources are not reported for areas inside Colowyo Federal coal 

leases and Preference Right Lease Application (PRLA) boundaries. Coal resources rounded to two significant figures] 

 Overburden categories (feet) Grand total 

 0-500 500-1,000 1,000-2,000 2,000-3,000 3,000-6,000 

By quadrangle 

AXIAL 66 64 48 0 0 180 

DEVILS HOLE GULCH 360 110 87 61 175 790 

EASTON GULCH 120 210 80 0 0 410 

MEEKER 22 23 96 45 61 250 

MONUMENT BUTTE 30 49 20 0 0 99 

NINEMILE GAP 410 460 210 85 0 1200 

PRICE CREEK 1.7 0 0 0 0 1.7 

RATTLESNAKE MESA 31 32 110 5.2 0 180 

THORNBURGH 91 75 18 0 0 180 

WHITE ROCK 26 20 20 11 33 110 

Grand total 1200 1100 690 210 270 3400 

By township 

T1N R94W 4.9 4.3 0.11 0 0 9.3 

T2N R92W 58 15 0.18 0 0 73 

T2N R93W 160 170 250 890 0 670 

T2N R94W 77 69 170 100 220 640 

T2N R95W 0 0 0.61 3.2 29 33 

T3N R92W 120 160 80 0 0 350 

T3N R93W 220 270 79 0 0 570 

T3N R94W 290 130 0.99 0 0 420 

T3N R95W 46 24 23 11 18 120 

T4N R92W 28 24 0 0 0 52 

T4N R93W 59 46 10 0 0 120 

T4N R94W 88 140 80 0 0 310 

T4N R95W 6.7 0 0 0 0 6.7 

Grand total 1200 1100 690 210 270 3400 

By ownership category 

Coal ownership Total Surface ownership Total 

Federal 3100 BLM 900 

Non-Federal 320 Private 2400 

 State 66 

Grand Total 3400 3400 

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M41
Table 10. Identified and hypothetical coal resources in millions of short tons for the FGC zone of the Fairfield coal group, Williams Fork Formation, Danforth H

county, reliability, overburden, and coal-thickness categories. 

[Resources are not reported for areas inside Colowyo Federal coal leases and Preference Right Lease Application (PRLA) boundaries. Coal resources rounded to two significa

County Reliability 0-500 feet overburden 

coal-thickness categories, in feet 

0-500 total 500-1000 feet overburden 

coal-thickness categories, in feet 

 2.3-3.5 3.5-7.0 7.0-14.0 >14.0 2.3-3.5 3.5-7.0 7.0-14.0 

Moffat Identified 1.6 5.9 74 380 470 0.64 11 120  Hypothetical 0 0 0 49 49 0 0 0 Moffat total 1.6 5.9 74 430 520 0.64 11 120 Rio Blanco Identified 0 0.6 24 610 630 0 3.5 14  Hypothetical 0 0 0 15 15 0 0 0 Rio Blanco total 0 0.6 24 620 645 0 3.5 14 Grand total 1.6 6.5 98 1100 1200 0.64 15 130 

County Reliability 1,000-2,000 feet overburden 

coal-thickness categories, in feet 

1,000-2,000 total 2,000-3,000 feet overburden 

coal-thickness categories, in feet 

 3.5-7.0 7.0-14.0 >14.0 2.3-3.5 3.5-7.0 7.0-14.0 >14.0 

Moffat Identified 9.4 31 190 230 0.36 2.1 0 0  Hypothetical 0 0 2.6 2.6 0 0 0 0 Moffat total 9.4 31 190 230 0.36 2.1 0 0 Rio Blanco Identified 7.6 32 390 430 0 5.5 13 150  Hypothetical 0 0 34 34 0 0 1.1 34 Rio Blanco total 7.6 32 420 460 0 5.5 14 180 Grand total 17 63 610 690 0.36 7.6 14 180 

County Reliability 3,000-6,000 feet overburden 

coal-thickness categories, in feet 

3,000-6,000 total Grand 

total 

 2.3-3.5 3.5-7.0 7.0-14.0 >14.0 

Moffat Identified 2.6 0.21 0 0 2.8 1200  Hypothetical 0.78 0 0 0 0.78 99 Moffat total 3.3 0.21 0 0 3.6 1300 Rio Blanco Identified 5.4 5.1 0.37 78 89 1800  Hypothetical 0.15 3.3 18 150 180 280 Rio Blanco total 5.6 8.3 18 230 270 2100 Grand total 8.9 8.5 18 230 270 3400 
Table 11. Identified and hypothetical coal resources in millions of short tons for the FGD zone of the Fairfield coal 

group, Williams Fork Formation, Danforth Hills coal field. 

[Resources are grouped in overburden categories and are grouped by county, township, and 71⁄2-minute quadrangle. Resources in 

coal- and surface-ownership categories are also reported. Resources are not reported for areas inside Colowyo Federal coal leases 

and Preference Right Lease Application (PRLA) boundaries. Coal resources rounded to two significant figures] 

 Overburden categories, in feet Grand total 

 0-500 500- 1,000 1,000-2,000 2,000-3,000 3,000-6,000 

By quadrangle 

AXIAL 43 39 13 0 0 95 

DEVILS HOLE GULCH 150 43 38 28 84 340 

EASTON GULCH 150 220 21 0 0 390 

MEEKER 23 24 76 27 37 190 

MONUMENT BUTTE 3.8 4.4 0.74 0 0 8.9 

NINEMILE GAP 190 170 110 68 0 540 

PRICE CREEK 0.70 0 0 0 0 0.70 

RATTLESNAKE MESA 60 68 150 2.2 0 280 

THORNBURGH 7.3 5.5 0.64 0 0 13 

WHITE ROCK 28 17 16 7.8 18 87 

Grand total 650 590 430 130 140 1900 

By township 

T1N R94W 5.0 3.2 0.02 0 0 8.2 

T2N R92W 34 7.8 0 0 0 42 

T2N R93W 120 130 260 71 0 580 

T2N R94W 42 48 110 54 120 370 

T2N R95W 0 0 0.29 1.2 11 11 

T3N R92W 12 17 5.9 0 0 35 

T3N R93W 93 100 7.4 0 0 200 

T3N R94W 150 74 0.12 0 0 220 

T3N R95W 40 18 17 7.5 13 96 

T4N R92W 3.8 1.4 0 0 0 5.2 

T4N R93W 43 29 5.2 0 0 77 

T4N R94W 100 160 21 0 0 280 

T4N R95W 4.6 0 0 0 0 4.6 

Grand total 650 590 430 130 140 1900 

By ownership category 

Coal ownership Total Surface ownership Total 

Federal 1700 BLM 500 

Non-Federal 180 Private 1400 

 State 29 

Grand Total 1900 1900 

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M43
Table 12. Identified and hypothetical coal resources in millions of short tons for the FGD zone of the Fairfield coal group, Williams Fork Formation, Danforth H

county, reliability, overburden, and coal-thickness categories. 

[Resources are not reported for areas inside Colowyo Federal coal leases and Preference Right Lease Application (PRLA) boundaries. Coal resources rounded to two significan

County Reliability 0-500 feet overburden 

coal-thickness categories, in feet 

0-500 

total 

500-1000 feet overburden 

coal-thickness categories, in feet 

 2.3-3.5 3.5-7.0 7.0-14.0 >14.0 2.3-3.5 3.5-7.0 7.0-14.0 

Moffat Identified 7.6 14 130 180 330 11 16 170  Hypothetical 1.6 0 0 0 1.6 0 0 0 Moffat total 9.2 14 130 180 330 11 16 170 Rio Blanco Identified 6.8 24 100 180 310 5.0 21 62  Hypothetical 0 0 6.0 0.67 6.6 0 0 8.0 Rio Blanco total 6.8 24 110 180 320 5.0 21 70 Grand total 16 38 240 360 650 16 37 240 

County Reliability 1,000-2,000 feet overburden 

coal-thickness categories, in feet 

1,000-2,000 total 2,000-3,000 feet overburden 

coal-thickness categories, in feet 

 2.3-3.5 3.5-7.0 7.0-14.0 >14.0 2.3-3.5 3.5-7.0 7.0-14.0 

Moffat Identified 3.9 10 25 8.0 48 0.78 1.4 0  Hypothetical 0 0 0 0 0 0 0 0 Moffat total 3.9 10 25 8.0 48 0.78 1.4 0 Rio Blanco Identified 1.8 8 3.8 350 360 2.5 3.8 5.8  Hypothetical 0 0.39 11 3.0 14 0.10 2.1 10 Rio Blanco total 1.8 8.9 15 350 380 2.6 6.0 15 Grand total 5.7 19 40 360 430 3.4 7.4 16 

County Reliability 3,000-6,000 feet overburden 

coal-thickness categories, in feet 

3,000-6,000 total Grand 

total 

 2.3-3.5 3.5-7.0 7.0-14.0 >14.0 

Moffat Identified 2.3 0.21 0 0 2.6 710  Hypothetical 0.78 0 0 0 0.78 2.4 Moffat total 3.1 0.21 0 0 3.3 710 Rio Blanco Identified 7.2 0.81 0 44 52 1100  Hypothetical 3.7 9.1 43 28 84 130 Rio Blanco total 11 9.9 43 72 140 1200 Grand total 14 10 43 72 280 1900 
Table 13. Identified and hypothetical coal resources in millions of short tons for the FGE zone of the Fairfield coal group, 

Williams Fork Formation, Danforth Hills coal field. 

[Resources are grouped in overburden categories and are grouped by county, township, and 71⁄2-minute quadrangle. Resources in coal- and 

surface-ownership categories are also reported. Resources are not reported for areas inside Colowyo Federal coal leases and Preference Right 

Lease Application (PRLA) boundaries. Coal resources rounded to two significant figures] 

 Overburden categories, in feet Grand total 

 0-500 500-1,000 1,000-2,000 2,000-3,000 3,000-6,000 

By quadrangle 

AXIAL 170 140 12 0 0 320 

DEVILS HOLE GULCH 270 100 110 96 350 920 

EASTON GULCH 410 670 0 0 0 1100 

MEEKER 45 57 170 67 110 440 

MONUMENT BUTTE 23 9.9 0.27 0 0 33 

NINEMILE GAP 750 470 180 83 0 1500 

PRICE CREEK 0.17 0 0 0 0 0.17 

RATTLESNAKE MESA 56 97 180 0.14 0 330 

THORNBURGH 30 8.6 0.10 0 0 39 

WHITE ROCK 71 71 97 82 240 560 

Grand total 1800 1600 750 330 700 5200 

By township 

T1N R94W 12.5 4.1 0 0 0 17 

T2N R92W 64 6.2 0 0 0 70 

T2N R93W 240 210 350 83 0 890 

T2N R94W 90 130 270 160 420 1100 

T2N R95W 0 0 2.7 11 97 110 

T3N R92W 83 69 15 0 0 170 

T3N R93W 470 360 4.6 0 0 830 

T3N R94W 320 120 0.14 0 0 440 

T3N R95W 88 77 100 78 180 520 

T4N R92W 28 2.0 0 0 0 30 

T4N R93W 170 86 0.95 0 0 260 

T4N R94W 260 560 0 0 0 820 

T4N R95W 7.3 0 0 0 0 7.3 

Grand total 1800 1600 750 330 700 5200 

By ownership category 

Coal ownership Total Surface ownership Total 

Federal 4500 BLM 1200 

Non-Federal 700 Private 3800 

 State 160 

Grand total 5200 5200 

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M45
Table 14. Identified and hypothetical coal resources in millions of short tons for the FGE of the Fairfield coal group, Williams Fork Formation, Danforth Hil

county, reliability, overburden, and coal-thickness categories. 

[Resources are not reported for areas inside Colowyo Federal coal leases and Preference Right Lease Application (PRLA) boundaries. Coal resources rounded to two sign

County Reliability 0-500 feet overburden 

coal-thickness categories, in feet 

0-500 total 500-1000 feet overburden 

coal-thickness categories, in feet 

 2.3-3.5 3.5-7.0 7.0-14.0 >14.0 2.3-3.5 3.5-7.0 7.0-14.0 >14.0 

Moffat Identified 3.6 3.9 24 810 840 4.0 3.9 9.9 920  Hypothetical 0 0 0.91 7.3 8.2 0 0 0 0 Moffat total 3.6 3.9 25 820 850 4.0 3.9 9.9 920 Rio Blanco Identified 0.37 1.2 14 950 960 0 0.09 7.0 640  Hypothetical 0 0 0 20 20 0 0 0 29 Rio Blanco total 0.37 1.2 14 970 980 0 0.09 7.0 670 Grand total 4.0 5.1 39 1800 1800 4.0 4.0 17 1600 

 - 1,000-2,000 

total 

20003000 feet overburden 

coal-thickness categories (feet) 

2,000-3,000 

total 

3000-6000 feet overburden 

coal-thickness categories (feet

County Reliability 7.0-14.0 >14.0 >14.0 >14.0 

Moffat Identified 9.2 52 61 19 19 25  Hypothetical 0 0 0 0 0 16 Moffat total 9.2 52 61 19 19 41 Rio Blanco Identified 1.7 630 630 250 250 270  Hypothetical 00 48 48 63 63 390 Rio Blanco total 1.7 680 680 310 310 660 Grand total 11 730 740 330 330 700 
Table 15. Identified and hypothetical coal resources in millions of short tons for the FGF zone of the Fairfield coal group, 

Williams Fork Formation, Danforth Hills coal field. 

[Resources are grouped in overburden categories and are grouped by county, township, and 71⁄2-minute quadrangle. Resources in coal- and 

surface-ownership categories are also reported. Resources are not reported for areas inside Colowyo Federal coal leases and Preference Right 

Lease Application (PRLA) boundaries. Coal resources rounded to two significant figures] 

 Overburden categories, in feet Grand total 

 0-500 500-1,000 1,000-2,000 2,000-3,000 3,000-6,000 

By quadrangle 

AXIAL 38 20 0.61 0 0 60 

DEVILS HOLE GULCH 107 60 83 72 250 570 

EASTON GULCH 400 110 0 0 0 510 

MEEKER 31 70 78 36 680 280 

MONUMENT BUTTE 5.9 4.0 0 0 0 9.9 

NINEMILE GAP 350 110 150 4.1 0 610 

RATTLESNAKE MESA 39 82 42 0 0 160 

THORNBURGH 20 4.3 0 0 0 24 

WHITE ROCK 51 46 60 67 170 400 

Grand total 1000 500 410 180 490 2600 

By township 

T1N R94W 5.8 0.12 0 0 0 5.9 

T2N R92W 13 0.09 0 0 0 13 

T2N R93W 120 150 190 4.0 0 460 

T2N R94W 75 120 150 100 280 730 

T2N R95W 0 0.08 5.1 14 84 100 

T3N R92W 49 24 2.6 0 0 76 

T3N R93W 240 34 0 0 0 270 

T3N R94W 170 1.8 0 0 0 170 

T3N R95W 59 51 63 60 120 360 

T4N R92W 1.5 0 0 0 0 1.5 

T4N R93W 32 11 0 0 0 43 

T4N R94W 270 110 0 0 0 380 

Grand total 1000 500 410 180 490 2600 

By ownership category 

Coal ownership Total Surface ownership Total 

Federal 2200 BLM 500 

Non-Federal 390 Private 2000 

 State 61 

Grand total 2600 2600 

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M47
Table 16. Identified and hypothetical coal resources in millions of short tons for the FGF zone of the Fairfield coal group, Williams Fork Formation, Danforth 

county, reliability, overburden, and coal-thickness categories. [Resources are not reported for areas inside Colowyo Federal coal leases and Preference Right Lease Application (PRLA) boundaries. Coal resources rounded to two signifi

County Reliability 0-500 feet overburden 

coal-thickness categories, in feet 

0-500 

total 

500-1000 feet overburden 

coal-thickness categories, in feet 

 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

Moffat Identified 3.6 0.73 16 38 480 540 1.1 0.66 6.42 21  Hypothetical 0 0 0 0 0 0 0 0 0 0 Moffat total 3.6 0.73 16 38 480 540 1.1 0.66 6.4 21 Rio Blanco Identified 0.1 0.61 6.7 39 400 450 0 0.05 0.89 12  Hypothetical 0 0 0 0 45 45 0 0 0 0 Rio Blanco total 0.1 0.61 6.7 39 450 500 0 0.05 0.89 12 Grand total 3.7 1.3 23 77 930 1000 1.1 0.71 7.3 33 

County Reliability 1000-2000 feet overburden 

coal-thickness categories (feet) 

1,000-2,000 

total 

2000-3000 feet overburden 

coal-thickness categories, in feet 

2,000-3,000 

total 

3000-6000 feet overburden 

coal-thickness categories (feet) 

 7.0-14.0 >14.0 >14.0 >14.0 

Moffat Identified 2.2 21 23 13 13 14  Hypothetical 0. 0 0 0.01 0.01 12 Moffat total 2.2 21 23 13 13 26 Rio Blanco Identified 6.0 320 330 99 99 160  Hypothetical 0. 62 62 68 68 300 Rio Blanco total 6.0 380 390 170 170 460 Grand total 8.2 400 410 180 180 490 
Table 17. Identified and hypothetical coal resources in millions of short tons for the FGG zone of the Fairfield coal 

group, Williams Fork Formation, Danforth Hills coal field. 

[Resources are grouped in overburden categories and are grouped by county, township, and 71⁄2-minute quadrangle. Resources in 

coal- and surface-ownership categories are also reported. Resources are not reported for areas inside Colowyo Federal coal leases 

and Preference Right Lease Application (PRLA) boundaries. Coal resources rounded to two significant figures] 

 Overburden categories, in feet 

 0-500 500-1,000 1,000-2,000 2,000-3,000 3,000-6,000 Grand total 

By quadrangle 

AXIAL 48 7.5 0 0 0 56 

DEVILS HOLE GULCH 12 5.9 9.9 8.9 28 64 

EASTON GULCH 160 0 0 0 0 160 

MEEKER 7.0 15 12 5.7 10 50 

MONUMENT BUTTE 11 0.28 0 0 0 11 

NINEMILE GAP 130 34 85 0 0 250 

RATTLESNAKE MESA 17 34 11 0 0 62 

THORNBURGH 9.3 0.10 0 0 0 9.4 

WHITE ROCK 4.2 3.4 4.1 4.7 11 27 

Grand total 390 99 120 19 48 680 

By township 

T1N R94W 0.51 0 00 0 0 0.51 

T2N R92W 3.7 0 0 0 0 3.7 

T2N R93W 46 63 97 0 0 200 

T2N R94W 15 20 22 14 35 100 

T2N R95W 0 0.04 0.48 1.1 6.3 7.9 

T3N R92W 42 11 0 0 0 52 

T3N R93W 94 2.7 0 0 0 97 

T3N R94W 29 0.01 0 0 0 29 

T3N R95W 4.6 3.7 4.2 4.2 7.3 24 

T4N R92W 1.5 0 0 0 0 1.5 

T4N R93W 26 0.25 0 0 0 26 

T4N R94W 130 0 0 0 0 130 

Grand total 390 99 120 19 48 680 

By ownership category 

Coal ownership Total Surface ownership Total 

Federal 600 BLM 110 

Non-Federal 80 Private 560 

 State 12 

Grand total 680 680 

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M49
Table 18. Identified and hypothetical coal resources in millions of short tons for the FGG zone of the Fairfield coal group, Williams Fork Formation, Danforth H

county, reliability, overburden, and coal-thickness categories. [Resources are not reported for areas inside Colowyo Federal coal leases and Preference Right Lease Application (PRLA) boundaries. Coal resources rounded to two significa

County Reliability 0-500 feet overburden 

coal-thickness categories, in feet 

0-500 total 500-1000 feet overburden 

coal-thickness categories, in fee

 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 7.0-1

Moffat Hypothetical 2.2 0 0.00 0 0 2.2 1.6 0 0 0  Identified 0.10 0.96 29 180 44 250 0 0 0.38 13 Moffat total 2.3 0.96 29 180 44 250 1.6 0 0.38 13 Rio Blanco Hypothetical 3.5 2.4 0.61 0 0 6.5 2.2 1.8 0.73 0  Identified 0.72 2.0 30 51 49 130 0.04 0.13 22 43 Rio Blanco total 4.2 4.4 31 51 49 140 2.2 1.9 22 43 Grand total 6.5 5.4 60 230 93 390 3.8 1.9 22 56 

County Reliability 1000-2000 feet overburden 

coal-thickness categories, in feet 

1,000-2,000 

total 

2000-3000 feet overburden 

coal-thickness categories, in feet 

 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 

Moffat Hypothetical 1.5 0 0 0 0 1.5 1.1 0 0  Identified 0 0 0 0 0 0 0 0 0 Moffat total 1.5 0 0 0 0 1.5 1.1 0 0 Rio Blanco Hypothetical 2.9 3.0 2.4 0 0 8.4 3.3 2.6 4.0  Identified 0 0 6.6 38 68 110 0 0 4.5 Rio Blanco total 2.9 3.0 9.0 38 68 120 3.3 2.6 8.5 Grand total 4.3 3.0 9.0 38 68 120 4.4 2.6 8.5 

County Reliability 3000-6000 feet overburden 

coal-thickness categories, in feet 

3,000-6000 

total 

Grand 

total 

 1.2-2.3 2.3-3.5 3.5-7.0 7.0-14 

Moffat Hypothetical 1.8 0 0 0 1.8 8.2  Identified 0 0 0 0 0 260 Moffat total 1.8 0.00 0 0 1.8 270 Rio Blanco Hypothetical 6.1 4.4 22 .63 33 63  Identified 0 0 9.2 4.3 14 350 Rio Blanco total 6.1 4.4 31 4.9 47 410 Grand total 7.9 4.4 31 4.9 49 680 
Table 19. Identified and hypothetical coal resources in millions of short tons for the Fairfield coal group of the Upper 

Cretaceous Williams Fork Formation, Danforth Hills coal field, Colorado. 

[Resources are reported in overburden categories and are grouped by county, township, and 71⁄2-minute quadrangle. Resources in 

coal- and surface-ownership categories are also reported. Resources are not reported for areas inside Colowyo Federal coal leases 

and Preference Right Lease Application (PRLA). Coal resources rounded to two significant figures] 

 Overburden categories, in feet Total 

 0-500 500-1000 1000-2000 2000-3000 3000-6000 

By county 

Moffat 3300 2900 1400 64 130 7800 

Rio Blanco 3600 2800 3100 1300 2300 13000 

Total 6900 5700 4500 1400 2400 21000 

By township 

T1N R93W 1.3 0 0 0 0 1.3 

T1N R94W 43 22 2.7 0 0 68 

T2N R92W 340 110 9.5 0 0 460 

T2N R93W 900 1000 1700 520 0 4100 

T2N R94W 450 480 990 590 1500 4100 

T2N R95W 0 .12 9.9 40 340 390 

T3N R92W 420 400 250 0 0 1100 

T3N R93W 1200 1100 340 0 0 2600 

T3N R94W 1500 690 120 0 0 2300 

T3N R95W 400 300 370 250 590 1900 

T4N R92W 80 66 2.0 0 0 150 

T4N R93W 400 260 61 0 0 720 

T4N R94W 1100 1300 640 0 0 3000 

T4N R95W 86 0 0 0 0 86 

T5N R94W .77 0 0 0 0 77 

Total 6900 5700 4500 1400 2400 21000 

By quadrangle 

AXIAL 450 370 180 0 0 1000 

DEVILS HOLE GULCH 1500 660 480 360 1200 4200 

EASTON GULCH 1600 1600 740 0 0 4000 

MEEKER 170 210 580 260 370 1600 

MONUMENT BUTTE 90 110 58 0 0 260 

NINEMILE GAP 2100 1900 1200 480 0 5700 

PRICE CREEK 45 .16 0 0 0 45 

RATTLESNAKE MESA 370 410 830 41 0 1700 

SAWMILL MOUNTAIN 25 0 0 0 0 25 

THORNBURGH 280 160 54 0 0 490 

WHITE ROCK 220 250 340 250 770 1800 

Total 6900 5700 4500 1400 2400 21000 

By ownership category 

Coal ownership Total Surface ownership Total 

Federal 19000 BLM 5100 

Non-Federal 2500 Private 15000 

 State 530 

Total 21000 21000 

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M51
structed for each of the seven coal zones in the Fairfi eld coal 

group (fi gs. 20–26).

The maximum overburden for the Fairfi eld coal zones 

was determined by integrating structure contours drawn on the 

top of the Upper Cretaceous Trout Creek Sandstone (base of 

the Fairfi eld coal group) of the Iles Formation (fi g. A on pl. 

1), basal elevations for each coal zone, and surface elevations 

imported from 1:24,000 Digital Elevation Models for the 14 

quadrangles within the Danforth Hills (fi g. 5). The areal extent 

of each zone was determined by integrating structure contours 

drawn on top of the Trout Creek Sandstone, the mean base 

elevation for each zone above the Trout Creek (table 3), and 

the Digital Elevation Models for the quadrangles to determine 

a zero overburden line. The zero overburden line is equivalent 

to a basal crop line for the coal zone (see Roberts and others, 

chap. C, this CD-ROM). For this study, the base of the FGA 

and FGB zones was drawn on the top of the Trout Creek 

Sandstone.

Coal Resources

Hancock and Eby (1930) reported an estimated original 

coal resource on a coal-group basis of 10.6 billion short tons 

to an overburden depth of 3,000 ft for the Meeker quadrangle. 

Landis (1959) reported an estimated original coal resource 

on an individual-bed basis of 7.9 billion short tons to an 

overburden depth of 3,000 ft for the Danforth Hills coal fi eld. 

Hornbaker and others (1976) reported an estimated original 

coal resource of 10.5 billion short tons to an overburden depth 

of 6,000 ft for the Danforth Hills coal fi eld.

Based on data derived from the present study, coal 

resources of about 21 billion short tons (table 19) in the identifi ed and hypothetical resource reliability categories (Wood and 

others, 1983) are estimated for the Fairfi eld coal group. This 

estimate includes all coal beds greater than 1.2 ft thick to 

an overburden depth of less than 6,000 ft. The calculated 

coal resources are shown for various categories (coal and 

overburden thickness; resource type, county, township, and 

quadrangle location; coal ownership) in tables 5–18; a summary is given in table 19. Sixty percent of the total coal (13 

billion short tons) is within the 1,000-ft overburden category, 

and more than 32 percent (6.9 billion short tons) is with the 

500-ft overburden category. More than 47 percent of the total 

coal resource is contained in the FGB (4.7 billion short tons) 

and FGE (5.2 billion short tons) coal zones; more than 88 

percent of the coal in these two zones is federally owned and 

administrated by the Bureau of Land Management. The FGE, 

FGF, and FGG zones in the northern two-thirds of the study 

area have signifi cant areas where the overburden is less than 

500 ft. About 32 percent of the total coal in the FGE, FGF, 

FGG zones (3.2 billion short tons), in the northern part of the 

study area, is within the 500-ft maximum overburden category.

Although the Danforth Hills coal fi eld contains estimated 

original resources of 21 billion short tons of coal in the Fairfi eld coal group, this fi gure does not refl ect economic, landuse, environmental, technological, and geologic constraints 

that may affect coal availability and recoverability (T.J. Rohrbacher, written commun., 1998). Some of the economic constraints involve costs to build or move infrastructures such as 

railroads, highways, and primary electrical transmission lines. 

Environmental restrictions include river valleys, towns and 

communities, wildlife habitat, and air-quality issues. Geologic 

constraints include faulting, coal-bed thickness, and the dip 

of the strata. Any combination of these constraints and (or) 

restrictions can reduce the amount of coal that is available and 

recoverable by as much as 10 to 20 percent of the original 

resource (Rohrbacher and others, 1994).

Within the Danforth Hills coal fi eld, the recoverable coal 

will be restricted because many of the deeper coals within 

the Fairfi eld coal group are too close together for longwall 

mining. Longwall mining methods causes controlled collapsing of overburden, including coal beds thus reducing the 

amount of recoverable coal. The thickness of the partings and 

splits can also limit the recovery of the coal being mined. 

Mining techniques can reduce the original resource; for example, longwall methods can restrict the recovery of thick beds 

where mining equipment is engineered for a limited range of 

coal-bed thickness, normally less than 14 ft. Another factor 

that may limit recoverability is that much of the total coal 

resource is deeper than 1,000 ft. Currently, coal is being 

mined, by dragline, and truck and shovel methods, from two 

zones (FGF and FGG) in the Colowyo strip mine. Future 

mining in the Danforth Hills coal fi eld will most likely be 

restricted to the areas adjacent to the Colowyo mine and its 

rail line by both longwall and stripping methods. Although the 

factors just discussed will reduce the amount of coal that can 

ultimately be recovered, we did not estimate the tonnages that 

might be affected.

References Cited

American Society for Testing and Materials, 1997, Standard classifi cation of coals by rank [ASTM designation D-388-95], in Petroleum 

Products, Lubricants, and Fossil Fuels: 1997 Annual Book of ASTM 

standards, v. 5, sec. 5, p. 168–171.

Barnum, B.E., and Bass, N.W., 1974, The Danforth Hills Known Coal 

Leasing Area, Moffat and Rio Blanco Counties, Colorado: U.S. Geological Survey unpublished geologic map and report supporting 

outline map, legal description, and minutes published in Federal 

Register, scale 1:62,500.

Brownfi eld, M.E., and Johnson, E.A., 1984, Selected references 

on the geology of the Danforth Hills coal fi eld, Moffat and 

Rio Blanco Counties, Colorado: U.S. Geological Survey Open-File 

Report 84-768, 28 p.

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, northeastern Piceance Creek 

and southern Sand Wash Basins, Colorado, in Stone, D.S., ed., New 

M52 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Interpretations of Northwest Colorado Geology: Rocky Mountain 

Association of Geologists, p. 293–295.

Gale, H.S., 1907, Coal fi elds of the Danforth Hills and Grand Hogback 

in northwestern Colorado: U.S. Geological Survey Bulletin 316-E, p. 

264–301.

Gale, H.S., 1909, Coal fi elds of northwestern Colorado and northeastern Utah: U.S. Geological Survey Bulletin 341-C, p. 283–315.

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Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M53
Click on image below to bring up high-resolution image of plate 1

Plate 1. Assessment of the distribution and resources of coal in the Fairfi eld coal group of the Williams Fork Formation, Danforth Hills coal 

fi eld, northwest Colorado.

M54 Geologic Assessment of Coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah
Appendix 1—Digital Files for Coal Exploration Drill Holes in the Danforth Hills 

Coal Field, Northwest Colorado, for which Data are Publicly Available

Appendix 1 contains the publicly available drill-hole database (110 holes—shown in table 1) used to asses coal resources in 

the Fairfi eld coal group Williams Fork Formation in the Danforth Hills coal fi eld, northwest Colorado. The location, lithologic, 

and stratigraphic data are available in ASCII format, DBF, and Excel spreadsheet fi les on disc 2 of this CD-ROM.

Appendix 2—ArcView Project for the Geologic Assessment of Coal in the 

Fairfi eld Coal Group, Williams Fork Formation, Danforth Hills Coal Field, 

Northwest Colorado

The digital fi les used for the coal resource assessment of the Fairfi eld coal group of the Williams Fork Formation, Danforth 

Hills coal fi eld, northwest Colorado, 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 2 of chapter M 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 them—is given by Biewick and Mercier (chap. 

D, this CD-ROM). Metadata for all digital fi les are also accessible through the ArcView project.

National Coal

Resource

Assessment

Click here to return to Disc 1 

Volume Table of Contents

Assessment—Distribution, Resources of Coal, Fairfi eld Coal Gp., Williams Fork Fm., Danforth Hills Coal Field, Colo. M55