The Quartz Mountain terrane, of unknown Mesozoic or Paleozoic age, is distinguished lithologically by the association of orthoquartzite with feldspathic sandstone and (or) volcanic rocks (Silberling, oral commun., 2006). Other rock types include metapelite, dolomite, and locally derived coarse clastic rocks (Silberling and John, 1989). This structurally disrupted mass is intricately intruded by and structurally brecciated with igneous rocks in the Lodi Hills. The structures that bound the intrusive rocks are thought to postdate the fault or faults on which the sedimentary rocks of the Quartz Mountain terrane were originally emplaced (Silberling and John, 1989). Exposures in the La Plata quadrangle mapped as the Mountain Well sequence, have here been assigned to the Quartz Mountain terrane (John and Silberling, 1994). These rocks are exposed in Churchill and northern Nye Counties.