The Upper Paleozoic Transitional Detrital-Carbonate Assemblage is composed of Mississippian, Pennsylvanian and Permian rocks locally exposed in the western portion of Elko, Eureka, Lander, and Nye counties. As restricted, this assemblage includes several formations originally assigned by Roberts and others (1958) to the "Overlap Assemblage".

These local units primarily represent coarse clastic sediments eroded from the emergent Antler orogenic belt and deposited within local and discontinuous basins. These units now unconformably overlap folded and faulted rocks of the Lower Paleozoic, Western Siliceous and Volcanic, Transitional, and Carbonate Assemblages. The Upper Paleozoic Transitional Detrital-Carbonate Assemblage is exposed within a narrow facies belt in eastern Lander and western Eureka and Nye, and Elko counties.