U.S. Department of the Interior

U.S. Geological Survey

Pamphlet to accompany Scientific Investigations Map 3240

Map Showing Principal Coal Beds and Bedrock Geology 

of the Ucross-Arvada Area, Central Powder River Basin, 

Wyoming
Cover photograph: Hills along the east side of the Powder River in the Arvada NE 71⁄2-minute quadrangle. 

Note the dark continuous zones of coal or carbonaceous shale (photograph by Carol Molnia).
Map Showing Principal Coal Beds and 

Bedrock Geology of the Ucross-Arvada Area, 

Central Powder River Basin, Wyoming

By Carol L. Molnia

Pamphlet to accompany Scientific Investigations Map 3240

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director 

U.S. Geological Survey, Reston, Virginia: 2013

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Suggested citation:

Molnia, C.L., 2013, Map showing principal coal beds and bedrock geology of the Ucross-Arvada area, central 

Powder River Basin, Wyoming: U.S. Geological Survey Scientific Investigations Map 3240, 11 p. pamphlet, 1 sheet, 

scale 1:50,000.
iii

Contents

Geographic and Geologic Setting—Central Powder River Basin.........................................................1

Description of Study Area ...................................................................................................................1

Previous Investigations.................................................................................................................................1

Current Investigation.....................................................................................................................................2

Methodology..........................................................................................................................................2

Stratigraphy ...........................................................................................................................................3

Coal Beds of the Ucross-Arvada Area..............................................................................................5

Smith Coal Bed.............................................................................................................................5

Roland Coal Bed (of Baker, 1929) ..............................................................................................8

Arvada Coal Bed ..........................................................................................................................8

Felix Coal Bed...............................................................................................................................8

Truman Coal Bed..........................................................................................................................9

Healy Coal Bed (also known as Ulm 2) ....................................................................................9

Walters Coal Bed (also known as Ulm 1).................................................................................9

Monument Peak Coal Bed........................................................................................................10

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

References Cited..........................................................................................................................................10

Figures

1. Index map showing location of Powder River Basin, Wyoming and Montana, 

and Ucross-Arvada study area within the Wyoming part of the basin ...............................2

2. Index map showing the geographic setting of the study area .............................................3

3. Generalized stratigraphic section showing relation of principal coal beds in the 

Ucross-Arvada study area ..........................................................................................................4

4. Coquinoid beds which represent the contact between the Tongue River Member 

of the Fort Union Formation and the overlying Wasatch Formation ....................................5

5. Arvada coal bed at locality number 11......................................................................................8

Tables

1. Small interval of the Wasatch Formation in the Clearmont 71⁄2-minute USGS 

quadrangle.....................................................................................................................................6

2. Location information for localities referenced in text............................................................7
iv

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Conversion Factors

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD 29).

Horizontal coordinate information is referenced to the North American Datum of 1927 (NAD 27).

Altitude, as used in this report, refers to distance above the vertical datum.

Inch/Pound to SI
Map Showing Principal Coal Beds and Bedrock Geology 

of the Ucross-Arvada Area, Central Powder River Basin, 

Wyoming

By Carol L. Molnia

Geographic and Geologic Setting—

Central Powder River Basin

The Ucross-Arvada area is part of the Powder River 

Basin, a large, north-trending structural depression between 

the Black Hills on the east and the Bighorn Mountains on 

the west (figs. 1, 2) within the Northern Great Plains physiographic province. The basin is an asymmetric syncline with 

a long, gently dipping eastern flank and a steeply dipping 

western flank. The study area is near the geographic center of 

the basin, on the westward-dipping east limb of the structure. 

Detailed information on the Powder River Basin’s depositional setting, coal resources, coal quality, coal-bed methane 

resources, and coal mining activity is given by Flores and 

others (1999), Scott and others (2010), and Osmonson and 

others (2011). 

In the study area, strata typically dip less than 1 percent 

to the west. However, several small-scale structures cause 

local increases in dip and changes in dip direction. Near some 

faults, dips increase to as much as 50 percent for short distances. Intervals between strata are relatively consistent over 

large areas, but can change significantly over small distances 

because of facies changes.

Description of Study Area

The study area is within the southern half of the Sheridan 

30' × 60' quadrangle, Wyoming and Montana (fig. 2). (See 

Ver Ploeg and Boyd (2003) for a geologic map of the Sheridan 

30' × 60' quadrangle.) Most of the study area is within Sheridan and Johnson Counties, Wyoming; the extreme eastern 

edge of the area includes part of Campbell County, Wyoming.

Most of the Ucross-Arvada area lies within the outcrop 

of the Wasatch Formation of Eocene age (fig. 3); the extreme 

northeast corner falls within the outcrop of the Tongue River 

Member of the Fort Union Formation of Paleocene age. 

Within the Powder River Basin, both the Wasatch Formation 

and the Tongue River Member of the Fort Union Formation 

contain significant coal resources.

The Ucross-Arvada area is located between the modernday coal mining areas around Sheridan, Wyoming, to the west 

and Gillette, Wyoming, to the east. Scott and others (2010) 

carried out an assessment of the coal geology, resources, and 

reserves of the Sheridan coalfield, and Luppens and others 

(2008) carried out a similar assessment of the Gillette coalfield. There are no active coal mines within the study area. 

Major named coal beds (fig. 3) can be traced across large 

parts of the study area. The strata also contain local coal beds 

that are much less extensive, but can reach significant localized thicknesses. Thin coal beds (less than 2.5 ft thick) are 

also common, as are zones of carbonaceous shale. The coal is 

mostly subbituminous in rank (Stricker and others, 2007).

Previous Investigations

The Ucross-Arvada area is located in parts of several 

historically designated Powder River Basin coal fields. All 

lands in Ranges 76, 77, and 78 W., (the approximate eastern 

half of the study area), fall within the Powder River Basin coal 

field of Stone and Lupton (1910). Lands in Rs. 79 through 

82 W. and Townships 54 and 55 N., (the northwestern part of 

the study area), are in the southeastern part of the Sheridan 

coalfield of Taff (1909). The remainder of the study area falls 

within the Buffalo coalfield as defined by Gale and Wegemann (1910). The lands in Ts. 52 and 53 N., Rs. 80, 81, and 

82 W., specifically, are within the Buffalo–Lake DeSmet area 

of Mapel (1959), which contains much of the coal within the 

Buffalo coalfield. Many of the coal beds named in the Spotted Horse coalfield (Olive, 1957) just east of the study area, 

extend into the area.

Although much of the study area has been previously 

represented in the reports referenced above, those publications contained planimetric maps without topographical data 

to show the vertical position of features. Furthermore, the coal 

bed maps in Stone and Lupton (1910), Taff (1909), and Gale 

and Wegemann (1910) are presented at a scale of approximately 1:250,000, which is too small a scale to easily relate 

map features to specific ground features. In addition, these 
2 Map Showing Principal Coal Beds and Bedrock Geology of the Ucross-Arvada Area, Central Powder River Basin, Wyoming

300 KILOMETERS

200 MILES

0

0

NORTH DAKOTA

SOUTH DAKOTA

MONTANA

WYOMING

UNITED STATES

CANADA

Powder River

Basin CAMPBELL

JOHNSON

SHERIDAN

Gillette

Sheridan

Study area

Figure 1. Index map showing location of Powder River Basin, Wyoming and Montana, and Ucross-Arvada study area (black polygons) 

within the Wyoming part of the basin (basin area in yellow). 

early mappers faced the problem that the area had not yet been 

completely surveyed. Taff (1909) stated, “The traverse lines 

between known section corners were long, and even when 

these lines are adjusted to each other and to the known corners 

the locations of many points are only approximately correct.”

It should be noted, however, that three coal bed maps of 

limited extent within this study area were previously published 

on 1:24,000-scale topographic base maps: the northern part of 

the Horse Hill quadrangle (Mapel, 1978a), the northern part 

of the Ucross quadrangle (Mapel, 1978b), and the Clearmont 

quadrangle (Molnia, 1988) (fig. 2). These three maps are 

included within the map of this report for sake of completeness in depicting the area’s coal beds.

Principal coal beds in eight 71⁄2-minute quadrangles 

directly north of this study area, in the Buffalo Creek-Clear 

Creek area, were mapped at 1:50,000-scale by Molnia and 

Orrell (1988) following the same photogrammetric and field 

methods as described below.

Current Investigation

The locations and elevations of coal beds are shown 

on a topographic base map (1:50,000 scale) for an area that 

includes ten 71⁄2-minute quadrangles covering some 500 

square miles. The plotting of data on this base offers many 

advantages over the earlier planimetric maps because it 

enables a more accurate depiction of coal bed location; correlation of map features to ground features; calculation of unit 

thickness, dip, overburden, and interburden (interval between 

coal beds); and modeling of regional structure.

Methodology

The entire study area was mapped by the author during 

1980‒1983, using photogrammetric techniques as described 

in Molnia (1983). By these means, geologic features were 

plotted precisely and automatically onto 1:24,000-scale 

topographic maps with use of true-color aerial photographic 

1:24,000 models. In areas where major coals have burned at 

the outcrop, the resulting red-orange clinker (rocks baked and 

fused by the burning of underlying coal) is in sharp contrast to 

the light-colored underlying rocks and marks the elevation of 

the base of the coal bed. In areas where coals have not burned, 

the elevation of the base of the coal bed was determined by 

tracing outcrops and by identifying intervals to marker beds. 

In both cases, the photogrammetric plotter drew the coalbed 

traces onto the topographic map. 

Parts of the Ucross-Arvada area were also field-mapped 

during 1980‒1983 to check photogrammetric mapping accuracy and to map coal bed outcrops that were not discernible 

on aerial photographs. Because of the size of the study area, 

not all coal beds were followed to their farthest extents in 

the field. Symbols shown on the map indicate places where a 

coal bed appeared to pinch out or split into minor coal beds, 
Current Investigation 3

109°00’

46°00’

45°30’

44°30’

45°00’

44°00’

43°30’

43°00’

42°30’

108°00’ 107°00’ 106°00’ 105°00’ 104°00’

0

0

25 50 75 100 KILOMETERS

25 50 75 100 MILES

1 2 3 4

5 6 7 8 9 10

1. Clearmont

2. Leiter

3. Arvada

4. Arvada NE

5. Horse Hill

6. Ucross

7. Julio Draw

8. Arpan Butte 

9. Jewell Draw

10. Lariat

Index to 71⁄2-minute

quadrangle maps

of the study area

 

BIRNEY BROADUS

RECLUSE

BUFFALO GILLETTE

General Outline of the

Powder River Basin

B L A C K H I L L S

M O U N T A I N S

B I G H O R N

MONTANA

WYOMING

Coal Investigations Map C–114

(Molnia and Orrell, 1988)

 

SHERIDAN

Figure 2. Index map showing the geographic setting of the study area, the Sheridan 30’ × 60’ quadrangle and adjacent 30’ × 60’ 

quadrangles (outlined in gray), and the individual 71⁄2-minute quadrangles (numbered) that constitute the Ucross-Arvada study area. 

Also indicated (striped) is the adjacent U.S. Geological Survey (USGS) Coal Investigations Map C–114 (Molnia and Orrell, 1988).

or could not be mapped farther because of lack of outcrop 

of coal or clinker. Other symbols shown on the map indicate 

places where a coal bed is buried by alluvial deposits. Hinrichs 

(1984) and Hallberg and others (1999) prepared maps of the 

surficial geology of the Sheridan 30' × 60' quadrangle. 

Stratigraphy

The coal beds (fig. 3) mapped in the Ucross-Arvada area 

are in the Tongue River Member of the Fort Union Formation of Paleocene age and the overlying Wasatch Formation of 

Eocene age. These beds represent the youngest of the Wyoming Powder River Basin coal beds; they are stratigraphically 

above the major Wyodak-Anderson coal zone (Ellis and others, 1999), which is also part of the Tongue River Member and 

is mined in the Gillette coalfield. In the study area, the contact 

between the Tongue River Member of the Fort Union Formation and the overlying Wasatch Formation stratigraphic units 

is conformable. The units are fairly similar in color—moderate brown, gray, and tan—and also in lithologic composition. 

Both units include sandstone and siltstone, gray mudstone or 

gray shale, and dusky-red-brown carbonaceous shale. Also 

both have coal beds, coquinoid limestones, and widespread 

deposits of red-orange clinker.

Olive (1957, p. 13) described the formational contact 

between the Wasatch Formation and the Fort Union Formation 

that was chosen within the Spotted Horse coalfield:

“Inasmuch as the Roland bed is not continuous in 

the Spotted Horse field and its top cannot be used 

as a convenient mappable horizon; the top of the 

(Tongue River) member was mapped on the top of 

a persistent, highly fossiliferous (coquinoid) unit 

of shale, sandstone, and limestone which occurs 

5-65 feet above the Roland bed....At most places 

the fossiliferous unit is easily recognized because 

of numerous pelecypod and gastropod shells that 

litter its outcrops; the most conspicuous components 

are beds of coquinal limestone that weather into 

grayish-white ledge-forming blocks.”

In the Recluse, Wyoming, area, directly east and northeast of this study area, Kent and Berlage (1980) also placed 

the Wasatch-Fort Union contact at the top of these same beds 
4 Map Showing Principal Coal Beds and Bedrock Geology of the Ucross-Arvada Area, Central Powder River Basin, Wyoming

Age Stratigraphic

unit

Interval

(ft)

Average

thickness 

of bed (ft)

Coal

bed

Walters (Ulm 1) 20

Monument Peak 17

Healy (Ulm 2)

Truman 4

Felix 3

Arvada 9 

coquinoid beds

Roland (of Baker, 

1929)

3

Smith 6 50–100

50–180

240–380

300–400

100–190

150–200

18

150–300

Wasatch Formation Fort Union Formation

Tongue River Member (part)

PALEOCENE

(part)

EOCENE

VERTICAL SCALE

0

30

0

100

200 60

FEET METERS

Figure 3. Generalized stratigraphic section showing relation of principal coal beds in the Ucross-Arvada study area. Vertical scale 

drawn on the basis of typical range of intervals (shown on left side of column) from base of one coal bed to base of the overlying coal 

bed. See text for description of coal beds. 
Current Investigation 5

of freshwater mollusk fossils. In the Ucross-Arvada study 

area, as in the Buffalo Creek‒Clear Creek area (Molnia and 

Orrell, 1988), the author also placed the Wasatch-Fort Union 

contact at the top of the coquinoid beds (fig. 4), because they 

are a persistent, obvious feature. The Arvada coal bed directly 

overlies the coquinoid beds in many places, and is within 

20 ft of the top of the coquinoid beds in most other places. So 

for the purposes of this map, the trace of the Arvada coal bed 

serves as the approximate contact between the Fort Union and 

Wasatch Formations. 

The measured section (table 1) shows the composition 

and character of a small interval of the Wasatch Formation in 

the Clearmont 71⁄2-minute quadrangle (from Molnia, 1988). 

The trace of the measured section is shown on the accompanying map in T. 55 N., R. 80 W., secs. 26 and 35. The measured 

section begins in a covered interval at an elevation of about 

4,160 ft, estimated to be the elevation of the Truman coal bed 

at this location, and continues to the elevation of the Walters 

(Ulm 1) coal bed at approximately 4,530 ft. 

Coal Beds of the Ucross-Arvada Area

In ascending order; see figure 3 for positions of coal 

beds and table 2 for locality information. In the years since 

the author completed field mapping (1983), Scott and others 

(2010) and Osmonson and others (2011) completed correlation 

of all significant coal beds in the Wyoming part of the Powder River Basin through use of extensive recent drilling data 

from coalbed methane development. This subsurface correlation system resulted in a regional standardization of coal bed 

names that may vary from coal bed names used in this report. 

Any differences in nomenclature are noted in the following 

discussions of each coal bed.

Smith Coal Bed

The only outcrops of the Smith coal bed in the study area 

are near the northeast boundary, in the Arvada NE 71⁄2-minute 

Figure 4. Coquinoid beds which represent the contact between the Tongue River Member of the Fort Union Formation and the 

overlying Wasatch Formation. The Arvada coal bed directly overlies the coquinoid beds in much of the Arvada-Ucross area as well as 

in the Buffalo–Clear Creek area (Molnia and Orrell, 1988). Photograph taken approximately three miles north of the study area, on the 

east side of the Powder River.
6 Map Showing Principal Coal Beds and Bedrock Geology of the Ucross-Arvada Area, Central Powder River Basin, Wyoming

Table 1. Small interval of the Wasatch Formation in the Clearmont 71⁄2-minute USGS quadrangle. Trace of measured section shown on 

map in T. 55 N., R. 80 W., secs. 26 and 35. Thickness in feet (from Molnia, 1988). 

Clinker of Walters coal bed (Ulm 1) at top of hill; elevation of base of clinker approximately 4,530 ft 32

Cover 18

Sandstone, fine, with concretions 3

Shale, gray 3

Siltstone, beige 3

Shale, gray and tan 15

Shale, dusky-red-brown 2

Shale, tan, top of mollusk shell horizons 6

Siltstone, ledge-forming 1

Shale, gray and tan, with shell horizons; forms light band due to whitish-gray (caliche?) veneer 63

Shale, dusky red-brown 5

Coal (local bed), some clinker laterally 1.5

Shale, red-brown and gray 3

Siltstone and shale, gray and tan; forms light-colored band due to whitish-gray veneer 10.5

Shale, dusky-red-brown, with 2 in. coal bed in middle 1

Shale, gray and tan, with mollusk shell horizons 12

Sandstone, whitish-gray, with trough crossbeds and log-shaped concretions 3

Shale, gray and tan 10

Clinker of the Healy coal bed (Ulm 2); elevation at base approximately 4,360 ft 10

Cover 22

Cover, outcrops of coquinoid slabs laterally 4

Cover 10

Shale, dusky-red-brown 1

Shale, carbonaceous 0.3

Shale, dusky-red-brown 0.3

Coal (local bed) 1.2

Shale, dusky-red-brown and gray 6

Shale, gray and tan, with mollusk shells 6

Mudstone, light-tan, forming prominent white band due to whitish-gray veneer; one thin shell zone 20

Siltstone, coarsening-upward, with resistant nodules 4

Mudstone, light-tan, forming prominent white band due to whitish-gray veneer; one thin shell zone 19

Sandstone, resistant 2

Shale, tan and gray 10

Shale, carbonaceous and red-brown, forming dark band, with coals as much as 3 in. thick; silicified wood, shell hash in top 4 in. 6

Shale, dusky-red-brown 2

Shale 24

Cover, base elevation approximately 4,160 ft 65

Total measured section (rounded) 405
Current Investigation 7

Locality number Coal bed Quadrangle Township Range Section Aliquot part

1 Smith, Roland, 

Arvada

Arvada NE 55N 77W 23 W 1/2

2 Arvada Arvada NE 54N 77W 10 NE 1/4

3 Arvada Arvada NE 55N 77W 34 E 1/2

4 Arvada Arvada NE 54N 77W 15 N 1/2

5 Arvada Arvada NE 54N 77W 2 NW 1/4

6 Arvada Arvada NE 54N 77W 3 NE 1/4

7 Arvada Arvada NE 54N 77W 2 SW 1/4

8 Arvada Arvada NE 55N 77W 34 SE 1/4

9 Arvada Arvada NE 55N 77W 34 SE 1/4

10 Arvada Arvada NE 55N 77W 34 SE 1/4

11 Arvada Arvada 54N 77W 21 NW 1/4

12 Arvada Arvada 54N 77W 16 N 1/2

13 Felix Lariat 52N 77W 3 W 1/2

14 Felix Arvada 54N 77W 18 SW 1/4

15 Felix Arvada 54N 78W 12 NW 1/4

16 Felix Arvada 54N 77W 19 E 1/2

17 Felix Arvada 55N 77W 30 S 1/2

18 Felix Leiter 55N 79W 36 NE 1/4

19 Felix Arvada NE 55N 76W 28 unknown

20 Felix Leiter 55N 78W 29 W 1/2

21 Felix Arvada 55N 78W 27 NW 1/4

22 Truman Arpan Butte 54N 78W 31 N 1/2

23 Truman Arpan Butte 53N 78W 6 NW 1/4

24 Truman Arvada 54N 78W 2 N 1/2

25 Truman Jewell Draw 54N 78W 34 NW 1/4

26 Truman Leiter 55N 79W 14 unknown

27 Healy Arpan Butte 53N 78W 19 unknown

28 Healy Arpan Butte 53N 79W 26 unknown

29 Healy Arpan Butte 53N 78W 17 unknown

Mapel 14 Healy Horse Hill 53N 82W 14 SW 1/4

Mapel 1 Healy Horse Hill 53N 82W 2 SE 1/4

Mapel 25 Healy Horse Hill 53N 82W 33 W 1/2

Mapel 43 Healy Ucross 53N 80W 5 NW 1/4

Mapel 93 Healy Ucross 53N 81W 11 W 1/2

Mapel 200 Healy Julio Draw 53N 80W 34 NW 1/4

Mapel 19 Walters Horse Hill 53N 82W 23 NW 1/4

Mapel 2 (1959) Walters Horse Hill 53N 82W 4 S 1/2

Mapel DH 1 Walters Horse Hill 54N 81W 29 W 1/2

Mapel 10 Walters Ucross 53N 81W 2 SW 1/4

Mapel 128 Walters Ucross 53N 81W 33 S 1/2

Mapel 5 Walters Ucross 54N 80W 30 W 1/2

Mapel 22 Monument Peak Horse Hill 53N 82W 26 SW 1/4

Mapel 2 (1978a) Monument Peak Horse Hill 54N 82W 36 NE 1/4

Table 2. Location information for localities referenced in text. Numbers preceded by “Mapel” are locality numbers taken from Mapel’s 

publications as stated in this report. Locations not shown on map. 
8 Map Showing Principal Coal Beds and Bedrock Geology of the Ucross-Arvada Area, Central Powder River Basin, Wyoming

quadrangle, along the banks of the Powder River. Olive 

(1957) described the Smith coal bed to the north, between 

Clear Creek and the Powder River, as having a total coal thickness of as much as 11 ft, broken by a parting 8‒30 ft thick. 

At one locality ( locality no. 1; number here and henceforth, 

refers to left column, table 2), the author measured the Smith 

coal bed to be 6.8 ft thick, which included a 0.3-ft parting 

about 2 ft below the top. The Smith coal bed is associated with 

a rosy pink clinker, which aids in identifying the coal bed.

Roland Coal Bed (of Baker, 1929)

The only outcrops of the Roland coal bed in the study 

area are near the northern boundary, along the Powder River 

and its small tributaries, and along the tributaries to Clear 

Creek. Almost all outcrops are in the Arvada NE 71⁄2-minute 

quadrangle. The coal bed is thin in this area, with thicknesses 

ranging from 2‒4 ft. At locality no. 1, it exists only as a zone 

of carbonaceous shale about 2 ft thick. Just north of the study 

area, in the Buffalo Creek‒Clear Creek area (Molnia and 

Orrell, 1988), the Roland consists of a zone of three to five 

thin coal beds separated by partings as much as 30 ft thick. In 

Scott and others (2010) and Osmonson and others (2011), this 

bed is called the Roland (from Baker). 

Arvada Coal Bed

The Arvada coal bed crops out along the Powder River 

and its tributary creeks, and was mapped in the Arvada NE 

and Arvada 71⁄2-minute quadrangles. In these quadrangles, the 

Arvada coal bed was measured at twelve localities (locality 

nos. 1‒12) as a solid bench of coal 5‒11 ft thick (fig. 5). The 

Arvada coal bed overlies prominent coquinoid beds in many 

places, which aids in identifying the coal bed. The base of 

the Arvada coal bed is used here as the approximate contact 

between the Fort Union and Wasatch Formations. In Scott and 

others (2010) and Osmonson and others (2011), this bed is 

called the Upper Roland Rider.

Felix Coal Bed

The Felix coal bed is present in the eastern half of this 

study area, but is considerably thinner than that described in 

the Spotted Horse coalfield to the east. In Scott and others 

(2010) and Osmonson and others (2011), this coal bed is also 

called the Felix. In that part of the Spotted Horse coalfield to 

the east, the bed has an average thickness of about 15 ft and at 

one locality is over 28 ft thick (Olive, 1957, p. 30).

Figure 5. Arvada coal bed at locality number 11. The coal bed was measured as a solid bench of coal 11 ft thick.
Current Investigation 9

In the Lariat 71⁄2-minute quadrangle, the author measured 

a Felix outcrop (locality no. 13) where some coal has burned, 

but 5 ft of coal remains. In the Arvada 71⁄2-minute quadrangle, 

measurements were made at four localities in which the Felix 

occurs essentially as a solid coal, with thicknesses of 2.5 ft 

(locality no. 14), 3.4 ft (locality no. 15), and 2.4 ft (locality 

no. 16), as well as a thickness of 2.4 ft that included a parting 

of 0.5 ft approximately in the middle (location no. 17). In the 

Leiter 71⁄2-minute quadrangle, the Felix coal bed at locality no. 

18 is at least 6.1 ft thick, which included two partings of 0.3 ft 

each. In the Arvada NE 71⁄2-minute quadrangle, the Felix coal 

bed at locality no. 19 is a solid bed 4.5 ft thick. In other localities in both the Leiter and Arvada 71⁄2-minute quadrangles 

(localities no. 20 and no. 21 respectively), the Felix coal bed 

forms zones of several thin (thickness from 0.5 – 2 ft) coal 

beds interbedded with carbonaceous shales. 

Truman Coal Bed

The Truman coal bed was traced from the Recluse, Wyoming, area (Kent and Berlage, 1980) east of the study area, 

where it originates as an upper split of the Ulm 2 bed as used 

by Olive (1957) in the Spotted Horse coalfield. (Note: This 

Ulm 2 bed is not equivalent to the Healy bed; see Healy discussion below.) The Truman coal bed extends westward in the 

study area to about the middle of the Clearmont quadrangle. In 

Scott and others (2010) and Osmonson and others (2011), this 

bed is called the Ucross.

In the northeast quarter of the Arpan Butte 71⁄2-minute 

quadrangle, the author measured two outcrops of the Truman coal bed: at locality no. 22 it is 4 ft thick, and at locality 

no. 23 is 5 ft thick, with no partings at either locality. In the 

Arvada 71⁄2-minute quadrangle, the bed (locality no. 24) was 

measured to be about 4 ft thick, which included a 1-ft parting 

approximately in the middle. In the Jewell Draw 71⁄2-minute 

quadrangle (locality no. 25), an incomplete section of Truman 

coal is 2.9 ft thick, and in the Leiter 71⁄2-minute quadrangle 

(locality no. 26), it forms a coal zone 11.2-ft-thick, containing 

(in ascending order) 2 ft coal, 2 ft parting, 3.1 ft coal, 1.6 ft 

parting, and 2.5 ft coal. 

Healy Coal Bed (also known as Ulm 2) 

The Healy coal bed as used by Mapel (1959) in the 

Buffalo‒Lake De Smet area is also known as the Ulm 2 coal 

bed, but is stratigraphically higher than, and not equivalent to, 

the Ulm 2 bed as used by Olive (1957) in the Spotted Horse 

coalfield. The Ulm name comes from Gale and Wegemann 

(1910), who considered the main coal beds in the Buffalo field 

to belong to the Ulm coal group as designated by Taff (1909) 

in the Sheridan coalfield to the north. 

In the study area, the Healy coal bed has burned in many 

places along its outcrop, forming thick clinker deposits. The 

bed is thickest in the west half of the Horse Hill quadrangle. 

It has a minimum thickness at a complete exposure of 13 ft, 

including thin shale partings, at locality Mapel 14 (Mapel, 

1959, p. 102 and pl. 18), but an incomplete section (locality 

Mapel 1) has 29.5 ft of solid coal, and a section containing a 

caved mine entry (locality Mapel 25) has over 20 ft of almost 

solid coal (Mapel, 1959, pl. 18). In the east half of the Horse 

Hill quadrangle, the Healy coal bed averages about 15 ft in 

thickness (Mapel 1959, p. 100).

Mapel (1978b) showed a maximum Healy coal thickness 

of 17.7 ft, including only a 0.3- ft parting, in the east half of 

the Ucross 71⁄2-minute quadrangle (locality Mapel 43), and a 

minimum thickness of 11.3 ft (locality Mapel 93) of solid coal 

in the west half. In the southwest quarter of the Julio Draw 

71⁄2-minute quadrangle (locality Mapel 200), the Healy coal 

bed contains 14.9 ft of solid coal (Mapel, 1959, p. 98).

In the Arpan Butte 71⁄2-minute quadrangle, the author 

measured three outcrops of the Healy coal bed. The first, locality no. 27, is an 11.7-ft zone composed of (in ascending order) 

2 ft coal, 1 ft parting, 3 ft coal, 1.2 ft parting, and 4.5 ft coal. 

The second (locality no. 28) is 15 ft thick, which included a 

2-ft parting below the top 5 feet of coal. The third outcrop 

(locality no. 29, close to the southeastern extent of the Healy 

coal bed in the study area) consists of an 8-ft-thick carbonaceous zone of only coaly shale and dusky-red-brown shale at 

the Healy coal level.

Approximately two miles west of the western edge of the 

study area, northwest of Lake DeSmet, drill holes described 

by Mapel (1959, p. 84‒85) encountered a thick coal bed 

tentatively correlated with the Healy bed and referred to as 

the Healy(?) bed. This coal bed is as much as 223 ft thick, but 

has limited extent, complex stratigraphy, and in many places 

is partially or totally missing because it has burned (Mapel, 

1959, pl. 14). 

 In Scott and others (2010) and Osmonson and others 

(2011), the Healy zone is divided into Upper Healy and Healy, 

with numerous coal and shale splits in between. In those 

reports, this bed is also called the Healy.

Walters Coal Bed (also known as Ulm 1)

The Walters coal bed as used by Mapel (1959) in the 

Buffalo‒Lake DeSmet area is also known as the Ulm 1 coal 

bed. The Ulm name comes from Gale and Wegemann (1910),

who considered the main coal beds in the Buffalo field to 

belong to the Ulm coal group as designated by Taff (1909) in 

the Sheridan coalfield to the north. In Scott and others (2010) 

and Osmonson and others (2011), this bed is called the Upper 

Healy. 

The Julio Draw 71⁄2-minute quadrangle is essentially the 

easternmost extent of the Walters coal bed on this map. In the 

Horse Hill, Ucross, and Julio Draw 71⁄2-minute quadrangles, 

the unit has burned extensively and produced large areas of 

clinker. In the Horse Hill quadrangle Mapel (1959, p. 102) 

reported isolated unburned exposures of the Walters coal bed 

that include a zone of carbonaceous shale in the southwest 

quarter of the quadrangle. He also noted 4.3 ft of coal in the 

northeastern part of the quadrangle (locality Mapel 2 (1959)) 
10 Map Showing Principal Coal Beds and Bedrock Geology of the Ucross-Arvada Area, Central Powder River Basin, Wyoming

and 23.5 ft of coal broken by many thin partings of shale in the 

middle of the quadrangle (locality Mapel 19). Mapel (1978a) 

described the Walters bed from a drill hole in the northeast 

part of the Horse Hill quadrangle (locality Mapel DH 1), in 

ascending order, as containing 21 ft coal, 5 ft carbonaceous 

shale, and 11 ft coal.

In the Ucross 71⁄2-minute quadrangle, Mapel (1959, p. 

100) reported two incomplete exposures of Walters coal with 

thicknesses of 6.6 ft (locality Mapel 10) and 17 ft (locality 

Mapel 128). Mapel (1978b) also reported a complete section 

of over 14 ft of coal with only a 0.2 ft parting in the northeast 

quarter of the quadrangle (locality Mapel 5).

Monument Peak Coal Bed

The Monument Peak coal bed is represented by isolated 

remnants of coal and clinker on high peaks in the Horse Hill 

71⁄2-minute quadrangle. Mapel (1959, p. 102) stated that in the 

southwest quarter of the quadrangle (T. 53 N., R. 82 W., locality Mapel 22):

 “....the bed contains an aggregate of 19 feet 6 inches of 

coal and 5 feet 4 inches of shaly coal and partings. Gale and 

Wegemann (1910, pl. 9) report that it contains 16 feet of coal 

without partings in a caved mine entry in the N1⁄2 sec. 34 ....”

Mapel (1978a) described an outcrop of the Monument 

Peak coal bed in the northeast quarter of the Horse Hill 

quadrangle (locality Mapel 2 (1978a)) as being 18.5 ft thick, 

of which 17.2 ft is coal, with the other 1.2 ft made up of six 

thin partings spaced approximately equally throughout the 

coal bed.

Acknowledgments

Bion H. Kent, U.S. Geological Survey, Denver, Colorado, 

shared his mapping expertise and his extensive knowledge 

of the area’s geology. Linda J. Berlage and S. Andrew Orrell 

assisted me in fieldwork. Technical reviewers Jon E. Haacke 

and Arthur C. Clark, and editor W.R. Keefer, U.S. Geological 

Survey, provided careful and thoughtful examination of this 

manuscript. I appreciate the assistance of Lymon S. Cazenave, 

Margaret S. Ellis, and James D. Hoffman, U. S. Geological 

Survey, in the preparation of the map and figures for publication. I am indebted to Christopher J. Potter, Margaret S. Ellis, 

and Vito F. Nuccio for their support of my status as U.S. 

Geological Survey Honorary Scientist Emeritus during the 

completion of this publication.

References Cited

Baker, A.A., 1929, The northward extension of the Sheridan 

coal field, Big Horn and Rosebud Counties, Montana: U.S. 

Geological Survey Bulletin 806‒B, p. 15‒67.

Ellis, M.S., Flores, R.M., Ochs, A.M., Stricker, G.L., Gunther, 

G.L., Rossi, G.S., Bader, L.R., Schuenemeyer, J.H., and 

Power, H.C., 1999, Gillette Coalfield, Powder River 

Basin—Geology, coal quality, and coal resources, in Fort 

Union Coal Assessment Team, 1999 resource assessment of 

selected Tertiary coal beds and zones in the Northern Rocky 

Mountains and Great Plains region: U.S. Geological Survey 

Professional Paper 1625‒A, chap. PG, 103 p. 

Flores, R.M., Ochs, A.M., Bader, L.R., Johnson, R.C., and 

Vogler, Daniel, 1999, Framework geology of the Fort 

Union coal in the Powder River Basin, in Fort Union Coal 

Assessment Team, 1999 resource assessment of selected 

Tertiary coal beds and zones in the Northern Rocky 

Mountains and Great Plains region: U.S. Geological Survey 

Professional Paper 1625‒A, chap. PF, 17 p.

 Gale, H.S., and Wegemann, C.H., 1910, The Buffalo coal 

field, in Campbell, M. R., ed., Contributions to economic 

geology, 1908, Part II—Mineral fuels: U. S. Geological 

Survey Bulletin 381, p. 137‒169. 

Hallberg, L.L., Case, J.C., Jessen, C.A., and Kirkaldie, A.L., 

1999, Preliminary digital surficial geologic map of the 

Sheridan 30' × 60' quadrangle, Sheridan, Johnson, and 

Campbell Counties, Wyoming, and southeastern Montana: 

Wyoming State Geological Survey Map HSDM 99‒5. 

Hinrichs, E.N., 1984, Surficial geologic map of the 

Sheridan 30' × 60' quadrangle, Wyoming and Montana: 

U.S. Geological Survey Miscellaneous Investigations Field 

Studies Map MF‒1693, scale 1:100,000. 

Kent, B.H., and Berlage, L.J., 1980, Geologic map of the 

Recluse 1° × 1⁄2° quadrangle, Campbell and Crook Counties, 

Wyoming: U.S. Geological Survey Coal Investigations Map 

C‒81‒D, scale 1:100,000.

Luppens, J.A., Scott, D.C., Haacke, J.E., Osmonson, L.M., 

Rohrbacher, T.J., and Ellis, M.S., 2008, Assessment of coal 

geology, resources, and reserves in the Gillette coalfield, 

Powder River Basin, Wyoming: U.S. Geological Survey 

Open-File Report 2008‒1202, 127 p. 

Mapel, W.J., 1959, Geology and coal resources of the 

Buffalo‒Lake DeSmet area, Johnson and Sheridan 

Counties, Wyoming: U.S. Geological Survey Bulletin 1078, 

148 p. 

Mapel, W.J., 1978a, Geologic map and coal sections of 

the northern part of the Horse Hill quadrangle, Sheridan 

County, Wyoming: U.S. Geological Survey Open-File 

Report 78‒793, scale 1:24,000.

Mapel, W.J., 1978b, Geologic map and coal sections of the 

northern part of the Ucross quadrangle, Sheridan County, 

Wyoming: U.S. Geological Survey Open-File Report 

78‒455, scale 1:24,000.
References Cited 11

Molnia, C.L., 1983, Use of the Kern PG‒2 photogrammetric 

plotter in geologic and coal-bed mapping, Powder River 

Basin, Wyoming, in Colwell, R.N., ed., Manual of remote 

sensing, (2d ed.): American Society of Photogrammetry, 

v. 2, p. 1808‒1814. 

Molnia, C.L., 1988, Map showing principal coal beds of the 

Clearmont quadrangle, Sheridan County, Powder River 

Basin, Wyoming: U.S. Geological Survey Miscellaneous 

Field Studies Map MF‒1991, scale 1:24,000. 

Molnia, C.L., and Orrell, S.A., 1988, Map showing principal 

coal beds and bedrock geology of the Buffalo Creek‒Clear 

Creek area, Central Powder River Basin, Wyoming and 

Montana: U.S. Geological Survey Coal Investigations Map 

C‒114, 1:50,000 scale. 

 Olive, W.W., 1957, The Spotted Horse coalfield, Sheridan 

and Campbell Counties, Wyoming: U.S. Geological Survey 

Bulletin 1050, 83 p.

Osmonson, L.M., Scott, D.C., Haacke, J.E., Luppens, J.A., 

and Pierce, P.E., 2011, Assessment of coal geology, 

resources, and reserves in the southwestern Powder River 

Basin, Wyoming: U.S. Geological Survey Open-File Report 

2011‒1134, 149 p.

Scott, D.C., Haacke, J.E., Osmonson, L.M., Luppens, J.A., 

Pierce, P.E., and Rohrbacher, T.J., 2010, Assessment of 

Coal Geology, Resources, and Reserves in the Northern 

Wyoming Powder River Basin, Wyoming: U.S. Geological 

Survey Open-File Report 2010‒1294, 137 p. 

Stone, R.W., and Lupton, C.T., 1910, The Powder River coal 

field, Wyoming, adjacent to the Burlington Railroad, in

Contributions to economic geology, 1908, Part II, Mineral 

fuels—Coal fields in Wyoming: U.S. Geological Survey 

Bulletin 381‒B, p. 115‒136. 

Stricker, G.D., Flores, R.M., Trippi, M.H., Ellis, M.S., Olson, 

C.M., Sullivan, J.E., and Takahashi, K.I., 2007, Coal 

quality and major, minor, and trace elements in the Powder 

River, Green River, and Williston Basins, Wyoming and 

North Dakota: U.S. Geological Survey Open-File Report 

2007‒1116, 31 p. 

Taff, J.A., 1909, The Sheridan coal field, Wyoming: U.S. 

Geological Survey Bulletin 341‒B, p. 123‒150. 

Ver Ploeg, A.J., and Boyd, C.S., 2003, Geologic map of the 

Sheridan 30' × 60' quadrangle, Sheridan, Johnson, and 

Campbell Counties, Wyoming and southeastern Montana: 

Wyoming State Geological Survey Map Series MS‒64, 

1:100,000 scale. 
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Molnia—Map Showing Principal Coal Beds and Bedrock Geology of the Ucross-Arvada Area, Central Powder River Basin, Wyoming—Scientific Investigations Map 3240