Outcrops of an ash bed at several localities in northern California and western Nevada belong to a single air-fall ash layer, the informally named Rockland ash bed, dated at about 400,000 yr B.P. The informal Rockland pumice tuff breccia, a thick, coarse, compound tephra deposit southwest of Lassen Peak in northeastern California, is the near-source equivalent of the Rockland ash bed. Relations between initial thickness of the Rockland ash bed and distances to eruptive source suggest that the eruption was at least as great as that of the Mazama ash from Crater Lake, Oregon. Identification of the Rockland tephra allows temporal correlation of associated middle Pleistocene strata of diverse facies in separate depositional basins. Specifically, marine, littoral, estuarine, and fluvial strata of the Hookton and type Merced formations correlate with fluvial strata of the Santa Clara Formation and unnamed alluvium of Willits Valley and the Hollister area, in northwestern and west-central California, and with lacustrine beds of Mohawk Valley, fluvial deposits of the Red Bluff Formation of the eastern Sacramento Valley, and fluvial and glaciofluvial deposits of Fales Hot Spring, Carson City, and Washoe Valley areas in northeastern California and western Nevada. Stratigraphic relations of the Rockland ash bed and older tephra layers in the Great Valley and near San Francisco suggest that the southern Great Valley emerged above sea level about 2 my ago, that its southerly outlet to the ocean was closed sometime after about 2 my ago, and that drainage from the Great Valley to the ocean was established near the present, northerly outlet in the vicinity of San Francisco Bay about 0.6 my ago.

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Structural analysis of the Queenie structure, a topographically prominent, southwest vergent asymmetric fold located 35 km west of Point Sal, constrains the timing and nature of late Neogene deformation in a transect across the central offshore Santa Maria Basin. Analysis of post‐Miocene sediments mantling the fold indicates that the Queenie structure was formed in a relatively brief episode of NE‐SW directed shortening between 5 and 3 Ma, apparently in response to the onset of compression normal to the North American/Pacific plate boundary. Retrodeformation of depth‐corrected cross sections constructed from an extensive set of common depth point seismic data demonstrates that the Queenie structure overprints a Miocene extensional basin and is a fault propagation fold that formed as compression changed the normal slip on the basin margin shear zone to reverse slip. Geometric constraints and seismic data suggest that the controlling shear zone dips moderately (30° to 50°) to the northeast and is essentially nonlistric to the base of the brittle crust at a depth of about 12 km. Structural analysis of cross sections further shows that average total post‐Miocene NE‐SW shortening across the Queenie structure is about 3 % (0.39 km across the 13‐km‐wide zone of folding) and that related shortening across the 40‐km‐wide central reach of the offshore Santa Maria Basin between the Hosgri fault and the Santa Lucia Bank fault during the same period is roughly 1–2% (0.4–0.8 km). High‐resolution seismic reflection data show small folds (structural relief less than 10% of the primary Queenie structure) in post‐early/late Pliocene sediments on the southwestern flank of the Queenie structure. These folds exhibit minor coaxial deformation along the flank of the structure, suggesting that very low rates of tectonic folding (of the order of 0.005 mm shortening per year) may continue to the present. The transient nature of the Pliocene compressional event that formed the primary Queenie structure and the relatively low rates of recent seismic activity in the central offshore Santa Maria Basin suggest that postearly/late Pliocene interplate shortening at this latitude has been largely accommodated outside the basin.