The Alamos Canyon Siltstone Member, here named, is the uppermost member of the redefined Peace Valley Formation of the Ridge Basin Group in the central Ridge basin, Los Angeles Co., CA. The Peace Valley is separated into five members by clastic tongues of the Ridge Route Formation of the Ridge Basin Group. Consists of gray-green shale, mudstone, and siltstone containing a few brown sandstone layers and vertebrate fossils. Extends laterally for 6100 m and interfingers laterally with the Violin Breccia to the southwest and the Apple Canyon Sandstone Member (new name) of the Ridge Route Formation to the northeast. Conformably overlies the Posey Canyon Shale Member (new name) of the Peace Valley, from which it is separated by a distinctive tuff horizon; conformably underlies the Apple Canyon Sandstone Member. Thickness is 1500 m at the type section. Age is late Miocene based on vertebrate (Kinsey Ranch fauna) and plant fossils from underlying units. (B1565)

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