Abstract

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. Almost all of the study area is within Sheridan and Johnson Counties, Wyoming.

Most of the Ucross-Arvada area lies within the outcrop of the Wasatch Formation of Eocene age; 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 map includes locations and elevations of coal beds at 1:50,000 scale for an area that includes ten 7½-minute quadrangles covering some 500 square miles. The Wasatch Formation coal beds shown (in descending order) are Monument Peak, Walters (also called Ulm 1), Healy (also called Ulm 2), Truman, Felix, and Arvada. The Fort Union Formation coal beds shown (in descending order) are Roland (of Baker, 1929) and Smith.

First posted April 22, 2013