Unit is named the Osito Canyon Shale Member of the Peace Valley Formation (revised) of the Ridge Basin Group. Exposed in the central Ridge basin, Los Angeles Co., CA, where clastic tongues of the Ridge Route Formation separate the Peace Valley Formation into five members. Consists of nonfossiliferous gray shale, mudstone, and interbeds of siltstone and sandstone. Extends laterally of 6,154 m and interfingers with the Ridge Route Formation undivided to the northeast and the Violin Breccia to the southwest. Conformably overlies the Fisher Spring Sandstone Member (new) and conformably underlies the Frenchman Flat Sandstone Member (new), both of the Ridge Route Formation. Thickness at the type section is 976 m. Age is late Miocene based on its stratigraphic position above the marine Castaic Formation and below the Cereza Peak Shale Member (new) of the Peace Valley Formation. (B1565)

Source: GNU records (USGS DDS-6; Menlo GNULEX).