Provenance of the upper-Miocene Briones Formation in the Central Diablo Range, California

Sandstone of the upper-Miocene Briones Formation in the southwest Livermore basin and along the western flank of the central Diablo Range was derived primarily from the Sierran volcanic arc, with lesser amounts derived from Coast Range uplands. Most feldspars and unmetamorphosed volcanic rock fragments are attributed to a Sierran source. Most polycrystalline quartz grains, sedimentary rock fragments, and metamorphic rock fragments are attributed to a Coast Range source.;Abundant Sierran detritus shows that Briones sandstone in the study area is related to Sierran-derived units of the Neroly Formation rather than the Coast Range-derived Orinda Formation. The Franciscan Complex of the central Diablo Range was the primary source of Coast Range detritus in the Briones Formation. The mixture of Sierran and Coast Range sediment indicates that the central Diablo Range uplands did not form a barrier to westward dispersal of Sierran sediment during this part of the late Miocene.