| The coeval upper Miocene-lower Pliocene Wilson Grove and Petaluma formations in the northern San Francisco Bay Area represent fluvial flood-plain to open-ocean deposition. Sediment was derived from the Franciscan Complex during the late Miocene, but by Pliocene time, detritus also was derived from Tertiary sedimentary sources in the eastern Bay Area.; The Wilson Grove and Petaluma formations are correlated to other Tertiary units in the eastern Bay Area based on similar clasts, stratigraphy, tephra units, and paleocurrent and paleontologic data. Unique veined sandstone clasts in the upper part of the Petaluma were derived from a source east of San José.; These data suggest that the Wilson Grove and Petaluma formations were displaced 67 km from similar units and source rocks of the eastern Bay Area along the Silver Creek-Hayward-Sonoma Valley-Healdsburg-Maacama fault system at 18 mm/yr from 5 to 2.5 Ma and 8 mm/yr from 2.5 Ma to the present. |
