Chapter SD

SUMMARY OF TERTIARY COAL RESOURCES OF

THE DENVER BASIN, COLORADO

By D. J. Nichols

in U.S. Geological Survey Professional Paper 1625-A
SD-ii

Contents

Introduction.........................................................................................................SD-1

Stratigraphy.........................................................................................................SD-1

Description of Coal Zone....................................................................................SD-2

Coal Quality........................................................................................................SD-3

Original Resources..............................................................................................SD-4

Production History..............................................................................................SD-4

Conclusions.........................................................................................................SD-5

References Cited.................................................................................................SD-6

Figures

SD-1. Geologic map of the Denver Basin.

SD-2. Index map of the Denver Basin.

SD-3. Generalized stratigraphy of uppermost Cretaceous and lower Tertiary

rocks in the Denver Basin.

SD-4. Generalized stratigraphy of the Denver lignite zone in the Scranton

district (central Denver Basin) and Ramah-Fondis area (southern

Denver Basin).

SD-5. Lignite bed of the Denver Formation in outcrop in Big Gulch, Elbert

County, Colorado, in the Ramah-Fondis area.

Table

SD-1. Ranges of analyses of Denver Formation lignite (as-received basis)
SD-1

INTRODUCTION

The Denver Basin of northeastern Colorado contains rocks predominantly of

Late Cretaceous and early Tertiary age (fig. SD-1). Coal of Tertiary (early

Paleocene) age is present in the upper part of the Denver Formation in the

basin (fig. SD-2). These coal deposits have low importance in the current

National Coal Resource Assessment. They are unlikely to be utilized within

the next 20-30 years because they are of lower quality than other coal

available in nearby areas. This report briefly summarizes the geology,

occurrence, quality, and production history of these coal resources.

Additional information can be found in the references. Coal deposits of Late

Cretaceous age that also are present in the Denver Basin are not discussed in

this summary.

STRATIGRAPHY

Figure SD-3 shows the generalized uppermost Cretaceous and lower

Tertiary stratigraphy of the Denver Basin. Coal (lignite) of early Paleocene

age is in the “Denver lignite zone” (Kirkham and Ladwig, 1979) within the

Denver Formation. The Denver Formation itself ranges in age from Late

Cretaceous (Maastrichtian) to early Paleocene. It overlies the Arapahoe

Formation of Late Cretaceous age, and it is partially overlain by the mostly

correlative Dawson Arkose, a unit of Maastrichtian to Eocene age present

primarily in the southern part of the basin, and which lacks significant coal

beds (Landis, 1959; Soister, 1978; Soister and Tschudy, 1978; Kirkham and

Ladwig, 1979; Kluth and Nelson, 1988). The Denver Formation ranges in

thickness from 600 to 1,580 ft and consists primarily of claystone, siltstone,

and fine-grained sandstone; it includes minor conglomerate beds and local
SD-2

lava flows. Carbonaceous shale and lignite are present in the upper 300-500

ft of the formation east of the basin axis (Kirkham and Ladwig, 1979).

As shown in figure SD-2, the Denver lignite zone has two principal areas of

occurrence within the basin, the Scranton district to the north, east of the city

of Denver, and the Ramah-Fondis area to the south (Landis, 1959). The

stratigraphy of the lignite zone differs in these two areas, as shown in figure

SD-4, and the names of the significant lignite beds differ as well. The coal

bed names are informal.

DESCRIPTION OF COAL ZONE

Outcrops of the Denver Formation lignite are scarce, and data on the

thickness and lateral extent of beds is based on drill holes (Kirkham, 1978a).

In the Scranton district the principal lignite beds range in thickness from 10

to 30 ft; the E lignite bed (also known as the Watkins bed) reaches a

maximum thickness of 54.5 ft, and it can be traced for as much as 24 mi

(Kirkham and Ladwig, 1979). There is no stratigraphic continuity of lignite

beds between the northern and southern lignite areas, however. The region

between the productive areas is nearly barren of lignite (Kirkham and

Ladwig, 1979).

In the Ramah-Fondis area the principal beds range in thickness from 5 to 10

ft or more except for the Wolf bed, which is the thickest; it ranges from 18 to

28 ft thick (Kirkham and Ladwig, 1979). In both areas, thinner lignite beds

are present also.

Most of the coal beds in the Denver lignite zone contain several non-coal

partings, at least some of which are deposits of volcanic ash; others are
SD-3

claystone, siltstone, or sandstone (fig. SD-5). Parting thicknesses range from

less than 0.1 in to more than 2 ft. The cumulative thickness of partings

amounts to 5-30 percent of the total thickness of individual beds (Kirkham

and Ladwig, 1979).

Detailed isopach maps of the principal lignite beds were published by

Kirkham and Ladwig (1979, plates 2-4) for both the Scranton district and the

Ramah-Fondis area. Brand and Eakins (1980, plates 12-22) published

isopach and structure maps of the lignite beds, an isopach map of

overburden, and cross sections of the Denver lignite zone in the WatkinsLowry area (Scranton district). In the Watkins area the E lignite bed is less

than 200 ft below the surface. Overburden thickness is highly variable in the

Ramah-Fondis area due to erosional downcutting by local streams.

Throughout much of this area the Comanche bed is within 200 ft of the

surface, although west of West Bijou Creek the overburden is more than 300

ft thick. Alluvial valley floors occupy parts of both areas.

COAL QUALITY

Kirkham and Ladwig (1979) state that most analyses of lignite from the

Denver Formation indicate that the rank of the coal is lignite A, although a

few thin intervals within thick beds may rank as high as subbituminous C

coal. The Comanche bed in the Ramah-Fondis area appears to have the

highest quality of all Denver lignite zone deposits. The ranges of typical

analyses are shown in table 1 (data from Tremain and others, 1996); detailed

data are available in Kirkham (1978b) and Khalsa and Ladwig (1981).
SD-4

Table SD-1. Ranges of analyses of Denver Formation lignite (as-received

basis)

Btu’s per pound Moisture (%) Ash (%) Sulfur (%)

 4,000-7,000 22-40 8-30 0.2-0.6

ORIGINAL RESOURCES

Landis (1959) estimated 489 million tons of lignite to have been originally

present in the Scranton district and 474 million tons in the Ramah-Fondis

area. Hornbaker and others (1976) revised these estimates upward to a total

of 12,469 million tons for all Paleocene coal in the Denver Basin. Kirkham

and Ladwig (1979) accepted an estimate of 10-15 billion tons of lignite to be

present in beds 4 ft or more in thickness within 1,000 ft of the surface in the

Denver Formation.

PRODUCTION HISTORY

Mining of coal from the Denver lignite zone apparently began in the late

1800’s. Peak production occurred in the 1920’s and 1930’s (Kirkham and

Ladwig, 1980). Total production from early mines operating in the Scranton

district was 35,789 tons (Kirkham and Ladwig, 1979). Five mines near

Ramah and four near Fondis, Colorado, were in operation between 1909 and

1940; they produced a total of 3,047 tons of lignite (Kirkham and Ladwig,
SD-5

1979). No mining of Denver Formation lignite deposits has taken place since

1940.

CONCLUSIONS

The last mine that extracted lignite from the Denver Formation closed in

1940. These resources probably will not be used in power plants in the next

20-30 years because of the relative abundance of coal of better quality in

nearby areas (Kirkham and Ladwig, 1980). Those areas include western

Colorado and northeastern Wyoming. The present and future importance of

the Denver Basin with regard to energy production is more closely linked to

oil and gas resources than to coal (Higley and others, 1995).
SD-6

REFERENCES CITED

Brand, K.E., and Eakins, Wynn, 1980, Coal resources of the Denver East 1/2 o

x 1o quadrangle, Colorado: Colorado Geological Survey, Resource

Series 13, 25 plates.

Higley, D.K., Pollastro, R.M., and Clayton, J.L., 1995, Denver Basin

Province, in Gautier, D.L., Dolton, G.L., Takahashi, K.I., and Varnes,

K.L., eds., 1995 National Assessment of United States Oil and Gas

Resources—results, methodology, and supporting data: U.S.

Geological Survey Digital Data Series DDS-30, Release 2.

Hornbaker, A.L., Holt, R.D., and Murray, D.K., 1976, 1975 summary of

coal resources in Colorado: Colorado Geological Survey, Special

Publication 9, 17 p.

Khalsa, N.S., and Ladwig, L.R., eds., 1981, Colorado coal analyses 1976-

1979: Colorado Geological Survey, Information Series 10, 364 p.

Kirkham, R.M., 1978a, Location map of drill holes used for coal evaluation

in the Denver and Cheyenne Basins, Colorado: Colorado Geological

Survey, Open-File Report 78-8.

_____ 1978b, Coal mines and coal analyses of the Denver and Cheyenne

Basins, Colorado: Colorado Geological Survey, Open-File Report 78-9.

Kirkham, R.M., and Ladwig, L.R., 1979, Coal resources of the Denver and

Cheyenne Basins, Colorado: Colorado Geological Survey, Resource

Series 5, 70 p., 5 plates.
SD-7

_____ 1980, Energy resources of the Denver and Cheyenne Basins,

Colorado: Colorado Geological Survey, Environmental Geology 12,

258 p., 2 plates.

Kluth, C.F., and Nelson, S.N., 1988, Age of the Dawson Arkose,

southwestern Air Force Academy, Colorado, and implications for the

uplift history of the Front Range: Mountain Geologist, v. 25, no. 1, p.

29-35.

Landis, E.R., 1959, Coal resources of Colorado: U. S. Geological Survey

Bulletin 1072-C, 232 p., 3 plates.

Soister, P.E., 1978, Geologic setting of coal in Denver Basin, in Pruitt, J.D.,

and Coffin, P.E., eds., Energy resources of the Denver Basin: Rocky

Mountain Association of Geologists, 1978 Symposium, p. 183-185.

Soister, P.E., and Tschudy, R.H., 1978, Eocene rocks in Denver Basin, in

Pruitt, J.D., and Coffin, P.E., eds., Energy resources of the Denver

Basin: Rocky Mountain Association of Geologists, 1978 Symposium,

p. 231-235.

Tremain, C.M., Hornbaker, A.L., Holt, R.D., Murray, D.K., and Ladwig,

L.R., 1996, 1995 summary of coal resources in Colorado: Colorado

Geological Survey, Special Publication 41, 19 p.
Eolian deposits

Alluvium

Gravel and alluvium

White River Formation

Wall MountainTuff

Basaltic flows in Denver Formation

Upper Dawson Formation

Denver and Lower Dawson Formations

Arapahoe and Denver Formations

Laramie Formation

Fox Hills Sandstone

Pierre Shale, undivided

Colorado Group

Dakota Group

Mesozoic and Paleozoic, undifferentiated

Fountain Formation

Pikes Peak Batholith

Biotitic gneiss and schist

Holocene

Oligocene

Eocene

Paleocene

Paleocene and Cretaceous

Upper Cretaceous

Lower Cretaceous

Mesozoic and Paleozoic

Middle and Upper Pennsylvanian

Precambrian

Figure SD-1. Geologic map of the Denver Basin.

ADAMS

LINCOLN

ARAPAHOE

BOULDER

DENVER

WELD MORGAN

DOUGLAS

TELLER

ELBERT

EL PASO

JEFFERSON

COLORADO

0

10

20

0

10

20

Miles

Kilometers

Colorado

Springs

Boulder

39 

40 

105 104 
ADAMS

ARAPAHOE

WELD

DOUGLAS

ELBERT

EL PASO

39o

40o

105o104o

Colorado

Springs

Boulder

Scranton district

RamahFondis

area

Denver 

metropolitan 

area

JEFFERSON

COLORADO

0

10

20

0

10

20

mi

km

Map scale

Figure SD-2. Index map of the Denver Basin (orange), Colorado, showing counties, the 

Denver metropolitan area, other major cities, area of occurrence of potentially strippable 

lignite (defined as beds less than 200 ft in depth, shown in gray on map) in the Denver 

Formation, and coalfields where mines were active in the past (black). The basin margin 

is drawn at the base of the coal-bearing part of the Upper Cretaceous Laramie Formation. 

Modified from Landis (1959) and Kirkham and Ladwig (1979, 1980).
Upper 

Cretaceous 

(part)

Paleocene

Eocene

(part)

Laramie Formation

Arapahoe Formation

Dawson Arkose

Denver Formation

Figure SD-3. Generalized stratigraphy of the uppermost Cretaceous and lower Tertiary 

rocks in the Denver Basin. Lignite deposits of early Paleocene age exist in the Denver 

Formation. Modified from Landis (1959) and Kirkham and Ladwig (1979), incorporating 

age data from Soister and Tschudy (1978) and Kluth and Nelson (1988).

S N
Denver

Formation

Denver

Formation

Dawson Arkose

Dawson Arkose

A lignite bed

B lignite bed

C lignite bed

D lignite bed

E lignite bed

unnamed 

 lignite beds

Wolf bed

Comanche bed

upper, middle,

and lower

 Kiowa beds

Bijou bed

Scranton district Ramah-Fondis area

Figure SD-4. Generalized stratigraphy of the Denver lignite zone in the Scranton district (central 

Denver Basin) and Ramah-Fondis area (southern Denver Basin). After Kirkham and Ladwig (1979); 

not to scale.
Figure SD-5. Lignite bed of the Denver Formation in outcrop in Big Gulch, Elbert

County, Colorado, in the Ramah-Fondis area. Note prominent non-coal parting.