ABSTRACT
Based on the most estimate by the US Geological Survey, northern and southern Rocky Mountain States contain an estimated 2.7 trillion tons of coal or about 67 percent of the nation’s four trillion tons of coal resources. As in most other Rocky Mountain states, Wyoming’s coals occur in rock sequences deposited during either the Cretaceous Period (some 66–135 million years ago) or during the younger Tertiary Period (38–66 million years ago). During both these periods, depositional environments and climates were at least periodically well suited to the development of densely vegetated swamps. Paleocene rocks crop out in all but the Black Hills Region and Goshen Hole Field. Paleocene rocks invariably contain coals although they are most prolific in the Powder River Basin and Hanna Field. The Eocene Wasatch Formation is the youngest coal-bearing rock unit of economic importance in Wyoming. The rank of Wyoming coal is lignite to high volatile A bituminous.
