Conglomeratic deposits are located along the east flank of the Big Horn Mountains in the Powder River Basin (Weaver & Flores, 1988). The age of these deposits are approximately middle Paleocene. U-Th/He apatite ages from the crystalline core of the Big Horn Mountains, have a minimum age of 62 mya, indicating exhumation and uplift of the Big Horn Mountains begin around the same time (Crowley etal. 2002). The Black Hills to the east appear to have been uplifted between the Puercan and mid-Torrejonian NALMA, roughly 64 mya (Belt et al. 1997).