Sedimentary strata on the Southern California shelf and slope (Point Conception to Dana Point) display patterns and rates of sediment accumulation that convey information on sea-level inundation, sediment supply, and oceanic transport processes following the Last Glacial Maximum. In Santa Monica Bay and San Pedro Bay, postglacial transgression is recorded in shelf deposits by wave-ravinement surfaces dated at 13–11 ka and an upsection transition from coastal to shallow-marine sediment facies. Depositional conditions analogous to the modern environment were established in the bays by 8–9 ka. On the continental slope, transgression is evidenced in places by an increase in sediment grain size and accumulation rate ca. 15–10 ka, a consequence of coastal ravinement and downslope resedimentation, perhaps in conjunction with climatic increases in fluvial sediment delivery. Grain sizes and accumulation rates then decreased after 12–10 ka when the shelf flooded and backfilled under rising sea level. The Santa Barbara coastal cell contains the largest mass of postglacial sediment at 32–42 × 10 9 metric tons, most of which occurs between offshore Santa Barbara and Hueneme Canyon. The San Pedro cell contains the second largest quantity of sediment, 8–11 × 10 9 metric tons, much of which is present on the eastern Palos Verdes and outer San Pedro shelves. By comparison, the mass of sediment sequestered within the Santa Monica cell is smaller at ~6–8 × 10 9 metric tons. The postglacial sediment mass distribution among coastal cells reflects the size of local fluvial sediment sources, whereas intracell accumulation patterns reflect antecedent bathymetric features conducive for sediment bypass or trapping.

We analyzed wave and wind data from 18 buoys in the Southern California Bight to characterize the spatial and temporal variability of the regional wave climate. Point Conception shelters most of the Bight from being directly impacted by North Pacific weather. The wave height inside the sheltered zone and to the east of the Channel Islands is less than half the wave height in the open ocean to the west. Within the sheltered Bight, storm waves (by proxy of being greater than the 95th percentile wave height for more than 6 hours) are mainly from the west, but long period swells ( T p >15 seconds) are mainly from the south-southwest. There are on average two to four storms during each winter month (November–March) and fewer than two storms per month for the rest of the year. The Channel Islands selectively block the westerly swells and make the wave climate in the Santa Barbara Channel different from the rest of the sheltered Bight. A statistically significant wave-height minimum exists in the area offshore Dana Point and Oceanside. The multiyear (2–23 years) wave-data records from all 18 buoys show negligible temporal trend, positive or negative. Like the wave climate, the long-term probability of sediment transport on the continental shelves of the Bight displays large difference between the sheltered and open-ocean (near Point Conception) sites. The return period of incipient sediment motion on the sheltered shelf breaks (one to five months) is at least two orders of magnitude longer than that on the Point Conception shelf break (0.6 day). Similar to the spatial distribution of wave heights, there is a systematic return-period maximum on the shelf off Dana Point and Oceanside.

Abstract Five well-expressed marine abrasion platforms, and up to 10 additional poorly expressed ones, are preserved from Point Conception to Gaviota in the western Transverse Ranges, southern California. The terraces, which range in elevation from 10 to over 300 m, and in age from 80 ka to over 1 Ma, record the long-term history of uplift for this region of rapid tectonic convergence. The lowest four terraces have direct age control and correlate to oxygen isotope stages 5a, 5c, 5e, and 7. The fifth terrace presumably correlates to stage 9. Age control is based on: (1) amino-acid stereochemistry on mollusk shells collected from the lower four terraces; (2) uranium-series analyses of bone and teeth from the first and fourth terraces and their alluvial covers; (3) the assemblages of molluscan fauna associated with the first, second, and third terraces; and (4) inferred long-term rates of uplift based on the ages and elevations of the terraces. The terraces are folded across the Government Point syncline near Point Conception. The shoreline angle for the 80-ka terrace decreases in elevation by 8 to 10 m across the hinge of the syncline, with respect to its elevation to the east and west. Furthermore, platform gradients are steeper on the north limb, indicating asymmetric synclinal deformation. Deformation of the lowest three terraces indicates average folding rates in the range of 2 to 9° per million years, consistent with the total post-Miocene deformation. Along with the changes in slope and elevation for the terrace platforms and shorelines, the presence of several flexural-slip bedding-plane faults cutting the platforms and their overlying deposits also supports active folding of the syncline. The South Branch of the Santa Ynez fault displaces all of the terraces that cross it. The vertical component of slip, based on displacement of the shoreline angle, indicates a vertical rate of 0.05 mm/yr. The horizontal component of the slip rate was not determined but must be low due to the lack of significant deflection of the shorelines beyond that of the modem shoreline. Our data clearly indicate that the westernmost Santa Ynez Mountains are actively folding in association with north-south crustal shortening across the Transverse Ranges. The rates of folding estimated from the rates of terrace deformation, however, suggest that only a small fraction of the total regional shortening is accommodated onshore: the balance is apparently accommodated offshore to the south in the Santa Barbara Channel.