The Lower Paleozoic Western Siliceous and Volcanic Assemblage is represented by Ordovician, and minor Silurian and Upper Devonian units exposed as remnants of the upper plate of the Roberts Mountains thrust. Discontinuous, lithologically variable exposures of this assemblage are present in eastern Lander, western Eureka and Nye, and northern Elko Counties within the evaluation area. Similar rocks are exposed to the west and to the north of the area in southern Idaho.

These allochthonous cherts, shales, quartzites, and minor sandstones, limestones, conglomerates, volcanic flows and pyroclastics are structurally contorted and imbricately thrusted as result of over 100 miles of transport eastward from their original depositional locales. Although structural complexity makes estimates of original stratigraphic position and thickness impossible, these slope to bathyal subduction zone lithologies may have locally exceeded 20,000 feet in thickness.

Lower Paleozoic Western Siliceous and Volcanic Assemblage

Devonian
    Slaven Chert
    Woodruff Formation
Silurian
    Fourmile Canyon Formation
    Elder Sandstone
    Noh Formation
Ordovician
    Palmetto Formation
    Vinini Formation
    Valmy Formation