Bopesta Formation
Bopesta Formation
middle Miocene
Fluvial and lesser lacustrine sediments with subordinate, interbedded volcanic deposits that crop out in the uplands northeast of Monolith and Tehachapi Valley. Sedimentary component is variable, consisting predominantly of volcaniclastic conglomerates, lithic to quartzose and arkosic sandstones, mudstones, and debris flow deposits, and is interstratified with subordinate pyroclastic deposits including tuff breccias, fluvially reworked tuff and waterlain pyroclastic fall, and basalt lava flows (Buwalda and Lewis, 1955; Dibblee, 1967; Dibblee and Louke, 1970; Quinn, 1987). Deposited in fluvial and somewhat lesser lacustrine environments (e.g., Quinn, 1987). Clast composition is predominantly volcanic material sourced from Cache Peak Volcanics (map unit cpv). Maximum thickness >1,000 m (Buwalda and Lewis, 1966) or 1,370 m (Quinn, 1987); however, stratigraphic boundaries and definitions vary between workers. Based on substantial vertebrate fauna, including several equine species, Quinn (1987) interprets the age to be late Hemingfordian to late Barstovian (~17 to ~13 Ma). Coles and others (1997) revise this age to late Hemingfordian to early Barstovian. They correlate their magnetostratigraphic data with chrons C5Adn to C5Cn1 (~16.3 to ~14.2 Ma per Ogg (2020)). Conformably overlies Kinnick Formation (Buwalda and Lewis, 1955; Quinn, 1987).