The seafloor off greater Los Angeles, California, has been extensively studied for the past century. Terrain analysis of recently compiled multibeam bathymetry reveals the detailed seafloor morphology along the Los Angeles Margin and San Pedro Basin. The terrain analysis uses the multibeam bathymetry to calculate two seafloor indices, a seafloor slope, and a Topographic Position Index. The derived grids along with depth are analyzed in a hierarchical, decision-tree classification to delineate six seafloor provinces—high-relief shelf, low-relief shelf, steep-basin slope, gentle-basin slope, gullies and canyons, and basins. Rock outcrops protrude in places above the generally smooth continental shelf. Gullies incise the steep-basin slopes, and some submarine canyons extend from the coastline to the basin floor. San Pedro Basin is separated from the Santa Monica Basin to the north by a ridge consisting of the Redondo Knoll and the Redondo Submarine Canyon delta. An 865-m-deep sill separates the two basins. Water depths of San Pedro Basin are ~100 m deeper than those in the San Diego Trough to the south, and three passes breach a ridge that separates the San Pedro Basin from the San Diego Trough. Information gained from this study can be used as base maps for such future studies as tectonic reconstructions, identifying sedimentary processes, tracking pollution transport, and defining benthic habitats.

A deep-sea core collected on the continental slope off northern California contains a pollen stratigraphy for the past 20,000 yr that can be correlated to the pollen stratigraphy from the upper section of Clear Lake core CL-73-4. The occurrence in one sequence of pollen, reflecting the local continental paleoclimates, and marine microfossils reflecting the local paleoceanography, allows a comparison of concurrent responses of the local ocean and adjacent continental area to global climate changes. The interpretation of the two data sets gives a complex progression of changes that are probably interrelated, such as upwelling that produced coastal fogs. The changes in climatic and oceanographic environmental conditions that occurred in response to the switch from global glacial to interglacial conditions was not a smooth progression of increasingly moderate regimes; rather, the changes appear to be a complicated series of states that suggests a disequilibrium mode lasting from about 15,000 to 5,000 yr ago.

ABSTRACT Analysis of wide-swath side-scan sonar (GLORIA) data from Eel River Basin shows the basin to have a distinctive surface morphologic and structural expression that documents the influence of interaction between the North American and Gorda Plates during the Quaternary. Elongate, north-trending anticlinal folds and thrust faults occur along and west of the basin axis out to the base of the continental slope. The deformation front defined by these structures increases in age to the west and evolves through a sequence of diapiric deformation in the east, followed by broad anticlinal folding, and finally by large-scale thrust faulting to the west. The deformation front curves inland to the southeast near the southern end of the basin. Young anticlinal folds, cored in places by diapirs, break through the seafloor. Additional information from photos, seismic-reflection profiles, and samples of the anticlinal folds show shale flowage and melange. GLORIA images show halos around rising dome structures, indicating active uplift. Submarine drainage patterns visible on the GLORIA sonographs are controlled by structure; channels and canyons follow fault traces in places and elsewhere are diverted by rising anticlines. Eel River Basin has a high rate of sediment input, and deposits are being deformed both by tectonic compression and by an abundance of slope failures that exceeds most continental margins. Debris slides on the seafloor, in association with growing anticlinal ridges, document recency of these processes.

Abstract The need to expand the search for energy resources in deeper marine environments has intensified the importance of better understanding the nature and origin of continental slope settings and of acquiring a working knowledge of their characteristics. It has been known for a number of years that coarse-grained mass-flow deposits beyond the shelf break can form major petroleum reservoirs (Barbat, 1958), and it is likely that these deep-water environments will continue to be future exploration targets (Hedberg, 1970; Curran et al, 1971; Gardett, 1971; Nagel and Parker, 1971; Yarborough, 1971; Cooke et al, 1972; Schlanger and Combs, 1975; Enos, 1977; Walker, 1978; Wilde et al, 1978). Recently, however, with the concept of plate tectonics, seismic stratigraphy, and advances in seismic-reflection technology, there has emerged a more sophisticated approach to understanding the developments of continental margins. This understanding has placed more emphasis on the geological history and petroleum potential of continental slopes (Burk and Drake, 1974; Weeks, 1974; Bouma et al, 1976; Thompson, 1976; Bloomer, 1977; Schlee et al, 1977; Mattick et al, 1978). This paper presents a practical guide for recognizing continental slope sequences. Criteria are presented that we believe are common, or could be common, to all slopes regardless of whether they are adjacent to active, passive or buttressed continental margins.