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Two Scripps Institution expeditions to the Gulf of California provided 28,000 new soundings in a poorly charted area. These new data have been the chief source of information for construction of contour charts which indicate the remarkable basins and extensive submarine fault scarps of the Gulf area. V-shaped trenches and flat-floored troughs abut against most of the mountainous east coast of Lower California with no appreciable intervening continental shelf. Various possible explanations of the scarps leading to these deeps are discussed, and their origin as fault scarps is shown to be the most likely. In general the trenches trend to the northwest-southeast, whereas the long dimension of the troughs is north-south. These same directions are prominently indicated in the coast line on both sides of the Gulf. Analogies are drawn between the sea-floor topography of the Gulf and that of the southern California area and the West Indies. The combination of large-scale vertical movements and horizontal shearing of the San Andreas type is suggested as a cause of the submarine topography.

During the expedition several hitherto unsounded submarine canyons were discovered, and others were explored. The canyons were found only in the southern portion of the Gulf; they are particularly well developed around the tip of southern California where the climate is less arid than farther north. Conspicuous absence of submarine canyons is found along the supposed submarine fault scarps. The topography of the canyons in the Gulf is strongly suggestive of subaerial erosion. The cutting appears to have been prior to the time of formation of the submarine fault scarps. Surveys around Guadalupe Island off Lower California, which were made en route to the Gulf, indicated possible canyons of amphitheater shape in the slopes off this volcanic mass, but the alternative explanation of volcanic collapse or explosion was considered somewhat more probable than that of submerged river valleys.

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