Pancho Rico Formation, Salinas Valley, California

Abstract

The Pancho Rico Formation of Pliocene age comprises sandy marine strata and interbedded finer grainr.d rocks. It generally overlies the marine Monterey Shale of Miocene age and underlies the nonmarine Paso Robles Formation of Pliocene and fleistocene( ?) age in southern Monterey County, Calif. Lo-~ally it lies on the basement complex or on the Santa Margalita Formation of upper Miocene age. It crops otrt from north of King City southeastward for more than 50 miles to beyond the Nacimiento River and Vineyard Canyon. The Pancho Rico contains sandstone, mudstone, porcelaneous mudstone, porcelanite, diatomaceous mudstone, and conglomerate. Where the Pancho Rico overlies the Monterey Shale, its lower contact is at the base of the stratigraphically lowest sandstone unit above the typically finer grained Monterey. where the Pancho Rico overlies the Santa Margarita Formation, its lower contact is at the top of the stratigraphically highest bed that contains Ostrea titan, a giant oyster characteristic of the Santa Margarita.