GEOLOGY OF THE NORTHWESTERN WIND RIVER MOUNTAINS, WYOMING

A high and broad area in the Wind River Mountains exposes pre-Cambrian metamorphics, predominantly gneiss, intruded by acidic and basic rocks. By mid-Cambrian time these were deeply eroded to the widespread peneplain of the interior United States. Paleozoic sediments of Middle and Upper Cambrian, Upper Ordovician, later Devonian, earlier Mississippian, Pennsylvanian, and Permian—the usual northwestern Wyoming section—outcrop in the vicinity of Green River lakes, in the north part of the western flank. Most of the Mesozoic rocks in northernmost Green River Basin are concealed, but Dinwoody, Chugwater, Sundance, Morrison, and Upper Cretaceous are known. Cenozoic deposits occur, but their dating is uncertain.

Laramide orogeny produced, in the Paleozoic area, folds, two major westward thrusts, and three minor upthrusts. Faulting is extensive in pre-Cambrian rocks, but the age of most of the faults is unknown.

A peneplain, thought to be late Cenozoic, bevels pre-Cambrian and Paleozoic rocks. Subsequently there was stream incision to a maximum depth of 3500 feet during five erosion stages or subcycles. There were apparently at least two Pleistocene glacial epochs, and about 25 glaciers still exist.