OFFSET EQUIVALENTS ALONG THE SAN ANDREAS FAULT SYSTEM WERE ORIGINALLY LINKED BY A FAULT-BOUNDED SLIVER OF MIOCENE STRATA IN THE VINCENT GAP REGION, SAN GABRIEL MOUNTAINS, SOUTHERN CALIFORNIA USA

A key constraint on determination of cumulative slip on the San Andreas and San Gabriel faults in southern California is provided by offsets of originally continuous uppermost Oligocene to lower Miocene nonmarine strata and interbedded volcanics of the Plush Ranch, Vasquez and Diligencia formations. Detailed geologic mapping and analyses of the Vincent Gap region of the San Gabriel Mountains, approximately 10 km west of Wrightwood, has revealed that strata previously mapped as a basal member of the upper Miocene Punchbowl Formation are instead lower and middle Miocene deposits. The lower Miocene strata, which contain interbedded volcanics, are equivalent to the Plush Ranch, Vasquez and Diligencia formations, and are offset from the Vasquez Formation to the northwest along the Punchbowl fault, a splay of the San Andreas fault. The middle Miocene strata and the upper Miocene Punchbowl Formation are equivalent to the Tick Canyon and Mint Canyon formations, respectively, which lie stratigraphically above the Vasquez Formation. Recognition of these correlations allows refinement of palinspastic reconstructions along the San Andreas, Punchbowl and San Gabriel faults, and, together with provenance and structural data, volcanic and detrital-zircon ages, and volcanic compositional data, improves our understanding of the tectonic evolution of southern California since initiation of the transform margin approximately 24 Ma.