The \\'incl River Basin, which occupies 8,500 square miles in central, vyoming, is typical of the large sedimentary and structural basins that formecl in the Rocky Mountain region cluring Laramide cleformation. Broacl 'belts of folded and faulted Precambrian, Paleozoic, ancl Mesozoic rocks surround the basin, including the Wind River Range on the west, the Washakie Range and Owl Creek and southern Bighorn Mountains on the north, the Casper arch on the east, and the Granite Mountains ou the south. Belntively undeformed lower Eocene rocks occupy the central part of the basin. Precambrian basement rocks exposecl in the cores of mountain ranges indicate n long ancl complex history of sedimentation, plutonism, metamorphism, ancl deformation during Precambrian time. noel, types nre chiefly granite, gneiss, and schist; abundant n1nfic dikes occur locally. During Paleozoic and much of Mesozoic time, central Wyoming was part of the forclancl bordering the Cordilleran geosyncline on the east.