K-Ar Dating of the Beginning of Tertiary Volcanism in the Mojave Desert, California

Abstract

Mojave Desert Tertiary volcanism began about 22 m.y. ago (beginning of the Miocene). The region is distinctive in the Basin and Range province in that earlier Tertiary intermediate to acidic volcanic rocks are rare or lacking. The Miocene and younger volcanic rocks are andesitic and silicic pyroclastic rocks with lesser amounts of andesite and basalt flows intimately associated with block faulting.