The Carboniferous rocks have been studied from Wells Canyon, Idaho, southward to Big Cottonwood Canyon in the northern Wasatch Mountains and eastward to Brush Creek Canyon in the eastern Uinta Mountains. Lithologic descriptions and faunal lists are given for the successions in the Logan quadrangle and vicinity, and in Weber, Big Cottonwood, Duchesne River, and Brush Creek canyons. Eastward in the Uinta Mountains the Madison formation grades into drab sandstones that interfinger with red beds. A thick and excellently exposed section of the Brazer formation at Dry Lake, Logan quadrangle, is described. The Brazer is traced eastward nearly to the Colorado State line. The Morgan formation extends southward from the type locality and eastward along both sides of the Uinta Mountains. A 5000-foot section of the Wells formation in Wellsville Mountain, west of Cache Valley, is described. The lithology and age of the Park City formation are discussed.
The lower part of the Morgan formation in Big Cottonwood Canyon is probably Bendian in age, the upper part Des Moines. The Morgan and Weber formations in the Uinta Mountains are Des Moines and are believed nearly synchronous with the lower part of the Wellsville Mountain exposure of the Wells and with the type section in Wells Canyon, although part of each of the last-named sections may be somewhat older (Bendian). Some evidence supporting a Permian age for the whole of the Park City formation is presented. The paleogeography of the area through Carboniferous time is reviewed.