The Punchbowl block is a fault-bounded crustal sliver in the eastern San Gabriel Mountains of southern California with important implications for conflicting reconstructions of the San Andreas fault system. Detailed mapping, determination of conglomerate-clast and sandstone compositions, and dating of detrital and igneous zircon of Oligocene–Miocene strata define two distinct subbasins and document initiation of extension and volcanism ca. 25–24 Ma, followed by local exhumation of the Pelona Schist, and transition from alluvial-fan to braided-fluvial deposition. Strata of the Punchbowl block correlate with those of other regions in southern California, confirming 40–50 km of dextral slip on the Punchbowl fault, and supporting reconstructions with 60–70 km of dextral slip on the San ­Gabriel/Canton fault and ~240 km of dextral slip on the southern San Andreas fault. Provenance and probable correlations of Punchbowl-block strata argue against 80–110 km of dextral slip on the San Francisquito–Fenner–Clemens Well fault and limit the time interval during which such slip could have occurred. Synthesis of these findings with previous work produces paleogeographic reconstructions of the Punchbowl block and its probable correlatives through time.

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