![[Backscatter of Los Angeles Margin]](/file/28640/USGS Pacific Sea-Floor Mapping Project, Multibeam Survey Images and Data.iso/pacmaps/images/la_mos.gif)
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Backscatter data were mapped at:
The almost featureless low backscatter of most of the continental shelf is interrupted by very high backscatter on the Santa Monica Plateau. The high backscatter areas represent outcrops of Pliocene sediment first mapped by Vedder (1). The plateau presently lies at less than 100-m water depths; consequently, during the Late Pliocene and Quaternary eustatic lower sea levels the plateau was exposed and sediment was stripped from the surface. Vestiges of these same outcrops (shown by high backscatter) can be seen on the west and south sides of the Palos Verde inner shelf. The remainder of the shelf appears uniformly low in backscatter intensity. A previously unidentified scissor fault trends across the lower Palos Verdes slope and a parallel fault at the base of the slope has captured the channel of Redondo Canyon and deflected it to the southeast along the base of slope for more than 4 km before it makes its way onto the Santa Monica Basin proper. The effects of the Los Angeles River extending across the continental shelf during each eustatic low sea level can be seen by the large sediment wedge that has buried the continental margin. Compare the steep and deeply incised continental slope off Malibu with the gently sloping and gullied slope directly west of Los Angeles. The Los Angeles River trended directly to this area until 1824 when it was permanently diverted toward Long Beach by a large flood. The shaded-relief image of the land surrounding Santa Monica Bay was constructed using USGS 7.5 minute DEMs (Digital Elevation Models). References: |