The most prominent Eocene paleogeographic elements of central California were the Sierran continental landmass on the east and the Salinian continental borderland on the west, both underlain by granitic crust and separated by a trough-shaped, deep-marine area underlain by oceanic crust. These linear elements trended approximately north-south, parallel with the edge of the continent. Erosion of the Sierran area yielded clastic detritus that was transported westward and deposited in successive fluvial, near-shore, shallow-marine, and deep-marine environments. The Salinian borderland, which probably had been detached from the Sierran landmass by pre-Eocene right-lateral faulting along its eastern edge, consisted of irregular island uplands interspersed with deep marine basin . Detritus eroded from these islands was deposited as submarine fans within the borderland basins and on the sea floor on the east and west. Microfossils indicate deposition in basins of bathyal to abyssal depths and unrestricted access to the ocean. The early Tertiary submarine-fan deposits are similar throughout the central Coast Ranges, and contain assemblages of proximal and distal turbidites, deep-sea conglomerates, grain-flow deposits, and hemipelagic shales. They differ from most modern deep-sea fan deposits and typical flysch sequences in that they are very thick, limited in areal extent, and consist mostly of coarse clastic detritus. The conglomerates contain coarse clasts, including boulders, and have very thick, irregular bedding. Proximal sandstones consist of Bouma ae to abc e sequences that are very thickly bedded and amalgamated, poorly graded to ungraded, commonly structureless, and contain large mudstone rip-up clasts and dish structures. Distal sandstones contain more complete Bouma sequences, a greater variety of sedimentary structures, and are graded. The borderland region was tectonically active during sedimentation, so that island source areas and depositional basins formed and changed abruptly. Submarine fan sedimentation was rapid, but the supply of sediment was probably not continuous for long periods of time. Paleocurrent directions are varied, reflecting the irregular distribution of source areas and depositional basins.

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