New 3D seismic-reflection data from the northern San Joaquin Valley (Great Valley forearc basin), California, provide the first convincing evidence of emergence and erosion of the Franciscan subduction complex during the Mesozoic. Syntectonic growth strata record an early Maastrichtian phase of deformation, which elevated the subduction complex above sea level. Once exposed, erosion generated a supply of sediment that built a progradational wedge (arcward) into bathyal waters of the forearc basin. The thickness and extent of these subduction complex–derived sediments argue for an areally extensive landmass located west of the forearc basin. Regional emergence of the subduction complex suggests that erosion served as a significant driver in the exhumation of Franciscan blueschists.

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