Coso Volcanics, young
Coso Volcanics, young
late to middle Pleistocene
Composed of rhyolitic domes and flows and basaltic cinder cones and flows typically erupted from low-volume monogenetic vents distributed across the southern Coso Range adjacent to southern Owens Valley. At least 19 basaltic cinder cones and 38 rhyolitic domes and flows represent bimodal volcanism in the middle to late Pleistocene (Duffield and others, 1980; Bacon, 1982; Simon and others, 2009) in contrast to more diverse and continuous compositions erupted in the older (late Miocene to Pliocene) volcanic field (map unit cov). Basalts are mildly alkalic and porphyritic, with up to 30% phenocrysts of olivine, plagioclase, clinopyroxene, and opaque oxides, and erupted from vents peripheral to rhyolitic foci between ~1.1 and ~0.4 Ma per K-Ar dating (Duffield and others, 1980). Rhyolites are typically phenocryst poor (<2%) and often contain mafic inclusions, with Ar-Ar sanidine ages ranging from ~613 to ~56 ka (Duffield and others, 1980; Simon and others, 2009). However, Burgess and others (2021) report zircon ages of ~78 to ~100 ka on the youngest rhyolites. Unconformably overlies older Coso volcanic and sedimentary deposits (map units cov, cos) and granitic bedrock (map unit Gm).