A submarine scarp extends westward from Cape Mendocino, California, for at least 1,200 miles. Its height at 70 miles from shore is about 10,500 feet, and 1,000 miles from shore it is about 8,420 feet. The maximum average slope from top to bottom ranges from 7° to 10°; but portions of the scarp 1,000 feet high have slopes as great as 18°-24°. The scarp lies on the south side of a ridge which has a gentler slope toward the north in most places. Similar, but smaller, ridges and scarps are found to the north and south of the Mendocino Scarp and are parallel to it. Regional bathymetry shows that the sea floor for hundreds of miles south of the scarp is about 1/2 mile deeper than the sea floor for hundreds of miles north. The scarp does not appear to be a seismically active submarine extension of the San Andreas fault, which passes out to sea at Cape Mendocino. Epicenters of submarine earthquakes trend northwest from Cape Mendocino rather than west along the Mendocino Scarp. The origin of the scarp is uncertain, but three hypotheses are considered. These suggest that it may be (1) a submerged "continental slope" between "continental" rocks to the north and oceanic rocks to the south, (2) a reverse fault, or (3) a strike-slip fault.
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Menard et al. (1952) studied this question.