Tunis volcanics
Tunis volcanics
early Miocene
A series of mafic to intermediate composition volcanic rocks interbedded with nonmarine sediments in the San Emigdio Mountains in the southwestern map area.
Predominantly fine-grained ophitic, and variably scoriaceous, basalt with phenocrysts of olivine ± feldspar, and lesser andesite flows and plagioclase porphyritic dacite (Nilsen and others, 1973; Kellogg and others, 2008; Chapman and Saleeby, 2012). Includes minor shallow intrusive component (e.g., diabase) and locally includes hornblende-rich pyroclastic fall deposit (Chapman and Saleeby, 2012).
Turner (1970) reported K-Ar ages ranging from ~22 to ~25 Ma; Dickinson (1997) reported ages of ~22.5 Ma. Thickness locally reaches ~450 m but is typically less (Nilsen and others, 1973). Often mapped as interbedded with, and a member of, the Tecuya Formation (map unit tec), though Kellogg and others (2008) note it is also interbedded with the Temblor Formation (map unit tmb).