Egill Hauksson, Crustal structure and seismicity distribution adjacent to the Pacific and North American plate boundary in southern California,  J. Geophys. Res., 105, 13,875-13,905, 2000.

The initial view is approximately to the north.  The most prominent features  are the higher upper mantle velocity beneath theContinental Borderland.   The red  (low-velocity) regions are the surficial (1km depth) expressions of  the southern San Joaquin Valley, the Los Angeles and Ventura Basins, and  the Imperial Valley.  The figure is plotted with a vertical exaggeration of about 5.