The eastern Owl Creek Mts. are part of a block of Precambrian and younger rocks moved upward and southward in early Eocene by a moderately high angle thrust fault. The toe of the thrust became broken by normal faulting and the part behind it became the Copper Mtn. arch. Cedar Ridge fault scarp in the southern part of the toe is composed of post-thrust arkoses of the lower Eocene Wind River Formation. Drill-hole data suggest that Wind River arkose exists in the subsurface north of Cedar Ridge fault, but in most of the toe, the Tepee Trail is underlain by Paleozoic and Precambrian rocks, indicating extensive erosion of the Wind River on the toe prior to Tepee Trail time. It is postulated that the Wind River horst blocks and perhaps the Steffen Hill complex were grabens at this time, and were faulted upward after Tepee Trail time.