Summary:
The Kemmerer coal field extends from Lincoln County into northern Uinta County, and is part of the Hams Fork coal region in western Wyoming . It includes coals within the Upper Cretaceous Adaville and Frontier formations exposed within the Lazeart syncline, which is a long, narrow, north-trending fold that parallels thrust faults associated with Sevier deformation in the Overthrust belt. As a result of this deformation, coal beds in the area typically dip 20–30 degrees westward, and offset along faults ranges from several hundred to more than 4,500 m (about 15,000 ft; Rubey and others, 1975).
Both the Adaville and Frontier formations were deposited along the western edge of the Cretaceous foreland basin, where coastal plain, littoral, and shallow marine environments of the Western Interior Seaway migrated across the region (Roberts and Kirschbaum, 1995). The Cenomanian to Coniacian Frontier Formation consists of nearshore and coastal deposits, and the Santonian to Campanian Adaville Formation was deposited in beach and coastal plain settings (Roehler and others, 1977; Roberts and Kirschbaum, 1995; Lynds and Slattery, 2017). Between the two units is the Hilliard shale, which overlies the Frontier Formation and underlies the Adaville Formation. Marine rocks of the Hilliard Shale represent a large-scale transgression of the sea westwards.
Coals in the Frontier Formation are divided into three stratigraphic coal groups: the Spring Valley coal group near the base (also known as the Carter coal group), the Willow Creek coal group in the middle of the formation, and the Kemmerer coal group (not to be confused with the Kemmerer coal field, a spatial designation that encompasses all mineable coal deposits in the Kemmerer area), which is in the upper part of the formation above the Oyster Ridge Sandstone Member. Spring Valley group coals are high volatile C bituminous (Townsend, 1960), and Willow Creek group coals are high volatile B to A bituminous (Berryhill and others, 1950). Coals in the Kemmerer group are high volatile B bituminous to high volatile C bituminous (Townsend, 1960). Most of these coals are less than 2 m (6 ft) thick (Glass, 1982).
In the Adaville Formation, coals are more common in the lower half of the unit, above the basal Lazeart Sandstone Member. Adaville Formation coals are thicker and more abundant than those in the Frontier Formation, but are lower rank, ranging from subbituminous B to C (Glass, 1982). The thickest Adaville coal bed, which is immediately above the basal Lazeart Sandstone Member, averages 24 m (80 ft) in the Kemmerer area (Glass, 1982).