Pennsylvanian, Permian, and Lower Triassic strata in the eastern Great Basin aggregate about 35,000 ft of dominantly marine clastic and carbonate rocks that accumulated in the eastern part of the Cordilleran miogeocline. Subsidence and hypersubsidence created the Sublett, Oquirrh, Arcturus, Park City, Bird Springs, and other sedimentary basins within this major downwarp of the earth's crust. Late Paleozoic and early Mesozoic tectonism within and adjacent to the miogeocline controlled contrasting realms of clastic and carbonate sedimentation. Highlands in western and northwestern Utah, in eastern and northeastern Nevada, and in southern Nevada, certain orogenic belts (e.g., Sonoma) were stripped, in places to their Precambrian cores, and provided abnormal thicknesses of se iment to adjacent mobile negative depocenters. The craton east of the tectonic hinge line provided additional sediment.

The Cordilleran miogeocline did not close its doors in chaotic orogenic spasms at the end of the Paleozoic. Contrarily, the changeover from Permian to Early Triassic was not a major diastrophic event. A paraconformity typifies the boundary at many places, with disconformities elsewhere. Up to 4,000 ft of Early Triassic sediments accumulated; by Middle Triassic time, a major reversal occurred: what had been a major negative mobile belt since late Precambrian time was now uplifted, although the region east of the hinge line became negative, and the hinge line was a fulcrum. The Cordilleran miogeocline was destroyed, and some of its sediments were stripped away, only to be recycled and deposited in the Rocky Mountain geosyncline on the east.

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