This paper presents an interpretation of the events that occurred in the building of the central Rocky Mountains and the intervening basins, as revealed by exposures in west central Wyoming. The outline of the area studied is shown in the accompanying index map, Figure 1. The principal exposures are along the northern edge of the Sweetwater Plateau. F. M. Endlich 1 described the topography of the region in 1879. The region north of the Sweetwater escarpment drains into the Wind River; that to the south drains into the Sweetwater River. The Sweetwater rim (Pl. 97A) extends northeastward from the southern end of the Wind River Range (Pl 94) for about 18 miles and then turns eastward for 35 miles to join the Rattlesnake Mountains. It has a steep north face, rising 600 to 800 feet above the general level of the Wind River Basin (Pl. 97A). Its . . .