Geology of the southern portion of Spanish Springs Valley Quadrangle, Nevada

Abstract

The region studied contains mostly Cenozoic flows and intrusive rocks, many of which comprise formations described earlier by workers in the Virginia City quadrangle. The oldest rocks mapped are metamorphosed Mesozoic volcanic and sedimentary rooks exposed near Vista. The flows which overlie the metamorphosed rooks at Vista and extend continuously southward to the Virginia City-Spanish Springs Valley quadrangle boundary have been mapped as part of the Alta rather than the Kate Peak formation. A large portion of the Cenozoic rocks, especially those of the Kate Peak formation, are intrusions. The name, "McCarran rhyolite" has been proposed by the writer for the two extrusive volcanic domes which occur north of Truckee Canyon. The basalt-andesite-daoite-rhyolite association present in the northern Virginia Range and southern Virginia Mountains is similar to the Cenozoic Cascade province of Washington, Oregon, and northern California. A palagonite-like alteration was noted in a few thin sections of Alta and Kate Peak rock. Lake sediments exposed in Truckee Canyon are believed to be a western facies of the Chloropagus (Mio-Pliocene) formation rather than the Truckee (Pliocene) formation. Faulting and folding in the region generally tread northeast or northwest.