Unit is named the Posey Canyon Shale Member of the Peace Valley Formation (revised) of the Ridge Basin Group. Is exposed in the central Ridge basin, Los Angles Co., CA, where the Peace Valley Formation is separated into five members by clastic tongues of the Ridge Route Formation. Consists of indurated gray shale, mudstone, dolomicrite, pyritic shale and siltstone, and gypsiferous siltstone and contains plant, fish, ostracode, and mollusk fossils. Lateral extent is 2,700 to 3,600 m; interfingers with the Violin Breccia to the southwest and the Ridge Route Formation undivided and its Apple Canyon Siltstone Member (new) to the northeast. Conformably overlies the Piru Gorge Sandstone Member (revised) of the Ridge Route Formation; conformably underlies the Alamos Canyon Siltstone Member (new) of the Peace Valley and is separated from it by a distinctive tuff horizon. Thickness is 1,000 m at the type section and ranges from 730 to 1,000 m. Age is late Miocene based on fossils [plants]. (B1565)

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