Briones Hills, Contra Costa Co., California, USA

Age: Cenozoic (2.588 - 33.9 Ma)

Stratigraphic Name: Agua Sandstone Member; Alferitz Formation; Altamira Shale Member; Antelope Shale Member; Big Blue Serpentinous Member; Branch Canyon Formation; Briones Formation; Button Bed Sandstone Member; Capistrano Formation; Carneros Sandstone Member; Castaic Formation; Cierbo Sandstone; Claremont Shale; Devilwater Silt-Gould Shale Member; Escudo Sandstone; Fish Creek Gypsum Member; Freeman Silt; Gallaway Beds; Hambre Sandstone; Hannah Formation; Hercules Shale Member; Jewett Sand; La Vida Member; Malaga Mudstone Member; McDonald Shale; McLure Shale Member; Media Shale Member; Modelo Formation; Monterey Formation; Neroly Formation; Olcese Sand; Oso Member; Oursan Sandstone; Painted Rock Sandstone Member; Pismo Formation; Pleito Formation; Point Arena Beds; Point Sal Formation; Puente Formation; Pullen Formation; Quail Lake Formation; Reef Ridge Shale; Rincon Shale; Rodeo Shale; Round Mountain Silt; Salinas Shale; Salt Creek Shale Member; Saltos Shale Member; Sandholdt Shale; San Onofre Breccia; San Pablo Group; Santa Margarita Formation; Santos Shale Member; Sisquoc Formation; Sobrante Sandstone; Soda Lake Sandstone Member; Soda Lake Shale Member; Soquel Member Split Mountain Formation; Sycamore Canyon Member; Temblor Formation; Tequepis Sandstone; Tice Shale; Topanga Formation; Twisselman Sandstone Member; Valmonte Diatomite Member; Vaqueros Formation; Vedder Sand; Whiterock Bluff Shale Member; Wimer Formation; Yorba Member

Description: Sandstone, shale, siltstone, conglomerate and breccia; in part Pliocene and Oligocene.

Lithology: Major:{sandstone,mudstone}, Minor:{siltstone,conglomerate}, Incidental:{gypsum}

Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. [133]

Age: Miocene (5.333 - 15.97 Ma)

Description: Sandstone, siltstone, conglomerate and shell breccia. The Briones Sandstone in this assemblage contains a tuffaceous layer with a K/Ar age of 14.5±0.4 Ma (Lindquist and Morganthaler, 1991). In the southern part of the assemblage, locally divided into: I member of Wagner, G member of Wagner (locally subdivided into conglomerate and limestone), F member of Wagner, E member of Wagner, and D member of Wagner. In northern part of assemblage, locally divided into: upper sandstone and shale member, Hercules shale member, and lower sandstone and siltstone member.

Reference: Graymer, R.W. Geologic Map and Map Database of the Oakland Metropolitan Area, Alameda, Contra Costa, and San Francisco Counties, California. U.S. Geological Survey Miscellaneous Field Studies MF–2342. [82]

Age: Miocene (5.333 - 23.03 Ma)

Description: Briones Formation in Hercules area consists of sandstone, siltstone, conglomerate and shell breccia. The Briones Formation in this assemblage contains a tuffaceous layer with a K/Ar age of 14.5±0.4 Ma (Lindquist and Morganthaler, 1991). Briones Sandstone in Martinez area consists of sandstone, siltstone, conglomerate and shell breccia.

Reference: Graymer, R.W., D.L. Jones, E.E. Brabb. Preliminary geologic map emphasizing bedrock formations in Contra Costa County, California. U.S. Geological Survey Open-File Report 94-622. [86]