The major fault zone of California is the San Andreas. Right-lateral displacements along this fault as great as 225 miles since late Eocene time and 175 miles since Oligocene-Miocene time have been proposed. Although post-middle Miocene displacements

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of about 65 miles are reasonably documented, greater displacements of older rocks are presently speculative and require more precise substantiation.

The late Eocene-to-Oligocene depositional histories of the southern San Joaquin Valley, east of the fault, and the Santa Cruz Mountain region, west of the fault, are symptomatic of a genetic relation. The upper Tejon, San Emigdio, Pleito, and lower Temblor Formations of the San Joaquin Valley are believed to be homologous with the San Lorenzo, Vaqueros, and lower Hester Formations of the Santa Cruz Mountains. No comparable sequence of rocks is known from intervening areas adjacent to the San Andreas fault; therefore post-Oligocene movements of about 225 miles are confirmed.

The late Eocene-to-Oligocene foraminiferal lineage of Uvigerina jacksonensis ^harr U. tumeyensis ^harr "Siphogenerina" nodifera ^harr "S." transversa occurs in both regions and corroborates the age relations of the formations.

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