Hamsfork Coalfield

Coalfields of Wyoming,  The Geological Survey of Wyoming, Daniel N. Miller, Jr., State Geologist, Bulletin 58, Bibliography of Wyoming Coal, by Gary B. Glass and Richard W. Jones

Main Kemmerer Coal Bed

This coal bed, variously called Kemmerer No. 1 or Frontier No. 1, is the thickest and most persistent coal bed in the Kemmerer Coal Group.  Stratigraphically, the Main Kemmerer bed lied 200 to 250 feet below the top of the Frontier Formation at least in the south-central portion of the coal field.

This bed, which is reportedly up to 20 feet thick in the southern part of Lincoln County, is typically split into two benches by a 6-inch-thick rock parting.  While the top bench is usually 10 to 16 feet thick, the lower bench is closer to 4 or 5 feet thick.  The rock parting reportedly thickens to 30 feet north and south of Kemmerer, and the two benches thin to 5 and 3 feet thick, respectively.  Occasionally, the Main Kemmerer bed exceeds 7 feet thick even in northern Uinta County.

Most underground mining in the Hams Fork Coal Field has been on this coal bed with extensive mining near Kemmerer and Diamondville in the east-central part of the field.  This coal bed was mined in the Brilklant No. 8 deep mine, which was the last operating underground mine in the field, closed in 1964.

The apparent rank of the Main Kemmerer coal bed varies from high volatile B to high volatile C bituminous, possibly due to different depths of burial.

Glass, Gary B. & Richard W. Jones, "Coal Fields and Coal Beds of Wyoming,."  reprint No. 47, 1992, page 158

The Hams Fork Coalfield
A Geological Process

by Janet Roberts Lott, 14 November 2001, unpublished.


Everyday people use electricity and glass products without consciously realizing where these products come from.  Coal is such an important part of our everyday life, in fact it is vital to our everyday life.  It is a natural resource that we use, and deplete everyday.  In addition, many people seldom understand where coal comes from and how it was formed.  This paper explores specifically a coalfield of southwestern Wyoming.  This paper gives general and basic information as to the location and formation of the Hams Fork Coalfield.  This paper will briefly explore three specific coal deposits within the Hams Fork Coalfield to help support the geological process.

The State of Wyoming contains vast coal deposits.  Timothy A. Moore and Jane C. Shearer (2001) report Wyoming has the second largest coal reserve in the United States, with 1.44 trillion tons.  Wyoming's coal industry has been significantly important to the state as a profitable resource.  In addition, the coal industry is responsible for shaping much of the history of Wyoming.  The importance of coal to Wyoming and its economy is incalculable.  At times coal is viewed as a resource rather than a geological process that took place millions of years ago.  An appreciation for the geological process is obtainable by examining the formation of coal deposits in Wyoming.  The purpose of this paper is to take a closer look at the geological formation and other characteristics of the Hams Fork Coal Field located in southwestern Wyoming.

The Hams Fork coal bed is the third largest deposit of coal in the state of Wyoming.  According to Gary B. Glass, Wyoming State Geologist, and Richard Jones (1992), the coal fields in the state of Wyoming lie beneath more than 53,000 square miles, which translates into 54 percent of the State (p.133).  Wyoming's coalfields fall into two coal-bearing provinces.  Glass and Jones report, "The coals in eastern Wyoming are within the Northern Great Plains Province, while all other coal deposits in the State are within the Rocky Mountain Province" (p. 133).  Accordingly, the Hams Fork coal deposit is located in the Rocky Mountain Province.  Within the state, Wyoming's coal deposits are divided into ten specific coalfields:  Bighorn Coal Field, Hanna Coal Field, Black hills Coal Field, Jackson Hole Coal Field, Goshen Hole Coal Field, Powder River Coal Field, Green River coal Field, Rock Creek Coal Field, Hams Fork Coal Field, and Wind River Coal Field (Glass and Jones, 1992, p.133).[See Appendix 1, Wyoming Coal Bearing Areas]  Furthermore, the ten specific coalfields are then divided into 45 individual coalfields.[See Appendix 2, Coalfields of Wyoming]  Thus, the Hams Fork Coalfield includes the coal bearing rocks of the Bear River, Frontier, Adaville, Blind Bull, and Evanston Formations (Glass and Jones, 1992, pp. 157-161).

The Hams Fork coalfield is located in portions of Uinta, Lincoln, and Teton counties.  Glass and Jones (1992) state, "As defined, the Hams Fork Coal Field is limited to those portions of the Thrust Belt that are underlain by coal-bearing rocks, but geological and structural complexities prevent a more accurate depiction at this scale" (p. 157).  Geologically, only an approximate location of the coalfield is available because the structural complexities prevent and accurate description.  According to Gary B. Glass (1978b), originally the United States Geological Survey only named four coalfields in the Hams Fork region, however after a revision, the boundaries currently include the entire region (p. 53).

Thee structural geology of the Hams Fork Coal Field is complex.  Thrust faults are common to the Hams Fork Coal Region and the faults usually thrust westward and sometimes they are north-south (Glass, 1978b, p. 53).  The Hams Fork coal region falls within the Absaroka and Darby Thrusts, and the Overthrust Belt, which is part of the vast system of mountain ranges and basins comprising the North American Cordillera.  According to Glass (1978b):
Folded Paleozoic and Mesozoic rocks are thrust eastward over folded Cretaceous rocks with the younger Cretaceous and Tertiary rocks of the area resting unconformably on top of these older rocks.  The coal-bearing rocks of the Hams fork Region now crop out in long narrow belts bounded by major thrust faults or eroded limbs of folds.  These same faults and folds form the Salt River and Wyoming Ranges of the region (p.53).
The Thrusting in the Hams Fork Region is common to the coal beds in southern and western areas of Wyoming. 

The Hams Fork Coal bed formed during the Cretaceous age or approximately 64.4 to 144 million years ago.  Other deposits of coal in the state of Wyoming, formed later during the Tertiary Period, about 36.6 to 66.4 million years ago.  Moore and Shearer (1993) note about Wyoming's coal deposits formations, "Cretaceous peat deposits were most often located in deltaic, coastal plain, or other near shore settings along the Cretaceous eperic seaway.  As a result, Cretaceous coal beds are generally laterally extensive but are relatively thin" (p.877).  Moore and Shearer (1993) continue, "In contrast, Tertiary coal beds accumulated as peats in smaller more localized sedimentary basins formed during the Laramide orogeny" (p. 877).  In both of the periods, Cretaceous and Tertiary, the environment and climate in the area that is now Wyoming, was complementary to the development of densely vegetated swamps.

Formerly, Wyoming was a low-lying flat area covered by an inland sea, and at times this sea would retreat which would allow rivers to flow through the swamps and marshes.  Coal beds developed from the remains of swamp vegetation, the stems, leaves, and tree trunks, of plants that died and then were partially decayed.  Fredrick J. Rich (1986) reports the plant species in Wyoming would have been ferns consisting of the "herbaceous vegetation" (p. 98) and a variety of trees both "conifers and hardwoods" (p. 98).  Charles C. Plummer, David McGeary, and Diane Carlson (2001) note, "Partial decay of the abundant plant material uses up any oxygen in the swamp water, so the decay stops and the remaining organic matter is preserved" (p. 135).  The partially decayed plant matter then forms a thick layer on the bottom of the swamp called peat.

Over time, the bog began to sink as the water covered it and retreated.  The partially decayed vegetation became buried under sediments of minerals, sand and rock.  Fredrick J. Rich (1986) reports the coal deposits in the Hams Fork area were buried and compressed with "fluvial sandstones, interdistibutary siltstones and clays, and occasional oyster beds that represent brief marine incursions" (p.98).  The layers of sediment compress, and the pressure and head of the earth eventually changed the peat into coal.

Coal is an organic sedimentary burnable rock.  Coal changes from a color of brown to black as the amount of carbon in the rock increases.  Because of carbon with the rock, the classification of coal is as a rock and not a mineral (Santucci, lecture 2001).  Priscilla Long (1998) describes coal as, "Composed mainly of the element carbon, it resulted from photosynthesis:  the conversion of the sun's energy into organic compounds that takes place in the leaves of green plants.  Coal is fossilized plant matter" (p.3).  The evolution took place millions of years ago, formed the coal and coal beds that make up the Hams Fork coal deposits.  Today, the estimation is that there is 49.61 billion tons of coal in the Hams Fork region (Glass and Jones, 1992, p. 156).

Coal varies in its make up and it is divided into four types:  lignite, subbituminous, bituminous, and anthracite (Plummer et al., 2001, p. 529).  Depending upon the make up of the various characteristics of the coal will determine the rank of the coal.  These various characteristics were caused by the heat and pressure upon the peat during formation.  The coal in the state of Wyoming varies from lignite to high volatile A bituminous (Glass and Jones, 1992, p. 136).  [See Map of Wyoming's Coal Deposits.] 

The Hams Fork Coal Field has subbituminous coals occupy the more central parts" (p.7) of Wyoming, and he continues, "although, in the case of the Hams Fork Region, subsequent erosion has relegated even the younger sub-bituminous coal-bearing rocks to narrow bands between faults and eroded folds" (p.7).  This makes the Hams Fork Coal Field unusual.

Within the Hams Fork region is the most notable Adaville Formation, which is located west of Kemmerer, and contains abundant amounts of coal.  According to Glass and Jones (1992),
The Upper Cretaceous Adaville Formation is without question the most important coal-bearing formation in the Hams Fork Coal Field.  Ranging from 2,900-4,500 feet thick, the basal 1,200 feet of inter-bedded shale, claystone, and standstone  of this formation contain up to 32 subbituminous coal beds, many of which are much thicker than other Upper Cretaceous coal beds in Wyoming (p. 157).

The Frontier Formation is located in Frontier, Wyoming.  This formation is the oldest coal- bearing part in the Hams Fork Coal Field.  According to Glass and Jones (1992), "The formation consists of alternating shale, sandstone, clay, and coal" (p.157).  the coal beds that occur throughout most of the Frontier Formation are mineable.  The Main Kemmerer coal bed lies 200 to 250 feet below the top of the Frontier Formation.  Glass and Jones (1991) report,
This bed, which is reportedly up to 20 feet thick in the southern part of Lincoln County, is typically split into two benches by a 6-inch-thick rock parting.  While the top bench is usually 10 to16 thick, the lower bench is closer to 4 or 5 feet.  The rock parting reportedly thickens to 30 feet north and south of Kemmerer, and the two benches thin to 5 and 3 feet thick, respectively (p. 160).
Most underground mining in the Hams Fork Coal Field has been on the Frontier Formation coal bed with extensive mining in the Main Kemmerer coal bed.

The Almy coal deposit, another notable formation in the Hams Fork Coal Field, is located north of Evanston near the town of Almy.  The Almy coal bed is the only named coal deposit in the Evanston Formation.  Glass and Jones (1992) report,
Between 1869 and 1950, more than 2.7 million tons of the Almy bed were mined near Almy, just north of Evanston.  Where it was mined, the Almy coal bed reached 28 feet thick, but it was characterized by numerous thin partings near the top and middle.  And upper 8-foot-thick bench, which splits off the main mined bed in places, evidently was never mined, possibly because it was of poor quality or because it aided roof support (p. 159).
The Almy coal bed is no linger mined.  The rank of the Almy coal bed is subbituminous A to high Volatile C bituminous (Glass and Jones, 1991, p. 159).

The Hams Fork Coal Field is located in the Rocky Mountain Province in Southwestern Wyoming.  This coal deposit is the third largest in the state, with the Adaville, Frontier, and Almy Formations being the most outstanding.  Geologically the Hams Fork Coal Field is structurally complex because of its location on the Overthrust Belt.  Understanding the complex geological process of the formation of the Hams Fork Coal Field, and its location, illustrates that coal within this region is not just a resource, but also a geological masterpiece that took millions of years to complete.

Sources Cited:
Glass, Gary B. (1978b).  The Geological Survey of Wyoming, Circular No. 9, Wyoming Coal Fields No. 9, Laramie, Wyoming, 1978.

Glass, Gary B. & Jones, Richard W. (1992) The Geological Survey of Wyoming, No. 47, Coal Fields and Coal beds of Wyoming.  Laramine, Wyoming.

Long, Priscilla (1989).  Where the Sun Never Shines.  Paragon House, New York.

Moore, Timothy A. and Jane C. Shearer (1993).  "Processes and possible analogues in the formation of Wyoming's coal deposits."  Geology of Wyoming.  Vol. 2. Cheyenne, Wyoming, Pioneer Printing and Stationery Company.

Plummer, Charles C., McGeary, David, & Carlson, Dianne (2001)  Physical Geology.  8th ed. New York, New York, McGraw Hill.

Rich, Fredrick J.  (1986).  Relationships between modern wetlands and ancient environments of peat deposition in Wyoming.  In Sheila Roberts (Ed.), The Geological Survey of Adjacent Areas, 1983 Conference Proceedings.  Laramie, wyoming (pp. 95-97).

Santucci, Vincent L. M.S. (2001 September 5).  Physical Geology 1100, Western Wyoming Community College.  Kemmerer, Wyoming.

University of Wyoming, Department of Geology and Geophysics (2000),  <http://home.gg.uwyo.edu/geologyinteracctive/wyogeology/wyoCoal.asp?Section+Geologyo/o20Interactive>.