Oso Canyon Formation of Dibblee [1967]
Oso Canyon Formation of Dibblee [1967]
early Pliocene(?) to late Miocene
Consists of a sequence of coarse interbedded alluvial deposits cropping out in the westernmost Mojave Desert region, in the southern map area between the Garlock and San Andreas faults. Dibblee (1967) describes these deposits as predominantly coarse and fluvial, including fanglomerate, conglomerate, sandstone, and siltstone. Fanglomerate consists of unsorted and subrounded clasts ranging from pebble to boulder size in a matrix of coarse arkosic sandstone. Conglomerates contain moderately sorted, pebble- to cobble-size clasts. Fanglomerate and conglomerate clasts consist of granitic detritus and weathered volcanics (especially rhyolite) sourced from the adjacent Neenach Volcanics (map unit nev). Sandstone is arkosic, friable, and fine to coarse grained or conglomeratic. Siltstone is micaceous, argillaceous to sandy and commonly pebbly. Originally mapped as Oso Canyon Formation by Dibblee (1967), this unit was later reassigned to the Santa Margarita Formation (e.g., Sims, 1989). However, the Oso Canyon name is retained here due to uncertain stratigraphic correlation between this occurrence and the Santa Margarita Formation across the Tehachapi Mountains to the northwest. Unconformably overlies Neenach Volcanics (thus the lower age limit is constrained to late Miocene) and overlies marine Monterey Formation; upper age limit is less well constrained, though generally regarded as early Pliocene.