The Upper Paleozoic Western Siliceous and Volcanic Assemblage includes cherts, shales, mudstones and siltstone, basalt and andesite, with minor limestones, calcareous quartzites, sandstones and conglomerate in Elko, Lander, Eureka, and northern Nye Counties (Fagan, 1962; Smith and Ketner, 1978; Stewart and McKee, 1977). These units most probably represent accretionary wedges originally deposited within subduction complexes. These units have been displaced eastward by the Antler and Sonoma orogenies and now represent parts of the upper plate of both the Devonian through Mississippian Roberts Mountains allochthon, and the Permian through Triassic Golconda allochthon.

These allochthonous and para-autochthonous Mississippian through Permian lithologies were deposited in a variety of marine environments from relatively shallow to deep marine. Reconstruction of depositional environment and thickness is made difficult by the siliceous and allochthonous nature of the lithologies.