In terms of the distribution of pre-Neogene rocks, the California Continental Borderland and associated coastal areas can be divided into the inner Borderland and the outer Borderland,each of which is floored with juxtaposed Mesozoic to Paleogene sedimentary sequences and a coeval melange resembling the Great Valley Sequence-Franciscan Complex couple of central and northern California. The stratigraphy of the Borderland shows local differences, and only the contemporary basins preserve more complete stratigraphic records that can be compared with each other. Seismic sequence analyses provide a basis for inferring that the Patton, Tanner, Santa Catalina, Santa Monica, San Pedro basins and San Diego Trough are floored with Franciscan-type basement, covered by Miocene to Hol cene sediments. The Santa Cruz, San Nicolas, and Santa Barbara basins are underlain by thick Mesozoic to Paleogene sequences draped by Miocene strata and filled with Paleocene to Holocene sediments. Generally speaking, Mesozoic to Paleogene sequences are composed of shallow- to deep-water siliciclastic deposits. The Miocene sequences are dominated by volcaniclastic and biogenic sediments, and the Pliocene to Holocene sequences are dominated by deep-water mass-flow deposits. Based on the available chrono-stratigraphic information, a preliminary interbasinal stratigraphic correlation can be established.

The tectono-stratigraphic history of the Borderland can be accounted for by the interactions between the East Pacific Rise and the North American continent. During Mesozoic to early Tertiary times, the Borderland was a part of an Andean-type continental margin characterized by the coeval accumulation of fore-arc basin sequences and trench melange. After the East Pacific Rise impinged on the North American continent in the late Oligocene, transform tectonism gradually replaced subduction as the triple junctions passed along the continent edge. In the middle Miocene,

End_Page 127------------------------

wrench processes transposed a piece of continental margin northwestward to form the outer Borderland, and caused formation of Borderland basins and deposition of widespread Miocene volcaniclastics and San Onofre-type sediments. After the major transform activity jumped to the present San Andreas fault in the late Miocene, tectonism dwindled in the offshore area and the residual transform forces gradually forged the present basin-and-ridge configuration.

Available stratigraphic information indicates that the Cretaceous and Eocene apparently were periods of high sea stand, as evidenced by extensive marine incursion in the coastal area, whereas the Paleocene and Oligocene are periods of relative low sea stand. The Miocene is a period of high sea stand marked by extensive biogenic pelagic sedimentation. The Miocene-Pliocene boundary is characterized by a transition from biogenic sedimentation to mass-flow deposition. A period of slow mass-flow sedimentation in the late Pliocene is attributed to reduced terrigenous sediment input during the sea-level rise.