Data from the Great Valley Group. Eight petrofacies (Stony Creek, Platina, Lodoga, Grabast, Boxer, Cortina, Los Gatos and Ramsey) in approximate order of decreasing age. The lower part of the Great Valley Group (Upper Jurassic and Lower Cretaceous) contains material eroded from accreted and deformed terranes formed by the arc-arc collision that occurred prior to initiation of the Franciscan-Great Valley-Sierra Nevada arc-trench system. By the Late Cretaceous, extensive batholithic terranes provided potassium-feldspar-rich arkosic detritus to the entire forearc basin. By the Paleogene, tectonic activity decreased in the forearc basin, and the basin was filled to sea level in most parts.--Modified journal abstract.

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