Coso Volcanics
Coso Volcanics
Pliocene to late Miocene
Composed of widespread basaltic vents and lava flows, and andesitic to rhyolitic domes, lava flows, and pyroclastic deposits localized in polygenetic volcanic centers, distributed across the Coso Range adjacent to the southern Owens Valley. Duffield and others (1980) reported K-Ar ages ranging from ~6 to 2.5 Ma. Novak and Bacon (1986) interpret two major late Miocene and Pliocene volcanic episodes: the first (~6 Ma; ~5 km3 eruptive volume) primarily erupted basaltic lavas with subordinate, intermediate to high-silica composition magmas (andesite to high-silica rhyolite); the second and most voluminous episode (~4 to 2.5 Ma; ~30 km3 eruptive volume) erupted diverse products and constructed polygenetic volcanic centers. They also interpret a third (Pleistocene) episode, which is represented by map unit covy.
Basalt is typically mildly porphyritic with several percent plagioclase and olivine phenocrysts, and less commonly clinopyroxene, and erupted from widely dispersed and commonly moderately to highly eroded monogenetic cinder cones, primarily in eastern part of Coso Range (Duffield and others, 1980; Novak and Bacon, 1986).
Andesite, dacite, rhyodacite, and rhyolite erupted from polygenetic volcanic centers near Haiwee Ridge and elsewhere. 
Andesite occurs primarily as moderately porphyritic lava flows with ≤15% phenocrysts of plagioclase, clinopyroxene, minor olivine, and rare orthopyroxene (Duffield and others, 1980).
Dacite occurs predominantly as pyroclastic deposits and mildly to moderately porphyritic (10-30%) lava flows with phenocrysts of plagioclase and quartz ± clinopyroxene ± orthopyroxene ± amphibole ± biotite, plus local / uncommon olivine and common accessory zircon, sphene, and opaque oxides; contains up to 30% andesitic to basaltic inclusions (Duffield and others, 1980).
Rhyodacite occurs as moderately porphyritic lava flows with ~20% phenocrysts of plagioclase, hornblende, biotite, opaque oxides, and quartz, and accessory clinopyroxene, orthopyroxene, apatite, zircon, and sphene in a glassy and perlitic groundmass, and as pyroclastic fall deposits including a ca. 3 Ma eruption from a center near the west margin of the field which blanketed the range with a few to several meters of pumiceous pyroclastic fall material (Duffield and others, 1980). 
Rhyolite occurs as volumetrically minor primary and reworked pyroclastic deposits intercalated with Coso Formation sedimentary strata (map unit cos), including a ~3.14 Ma unwelded, pumiceous pyroclastic flow and fall deposit (Power, 1958; Duffield and others, 1980).