Fig. 287.—Map of San Clemente Island, California, showing the characteristic topography of recent uplift (after U. S. Coast and Geodetic Survey).
The contrasted islands of San Clemente and Santa Catalina.—Perhaps the most striking example of simultaneous opposite movements observable in neighboring portions of the earth’s crust is furnished by the coast of southern California. The coast itself at San Pedro and the island of San Clemente, some fifty miles off this point, in common with most portions of the neighboring coast land, have been rising in interrupted movements from the sea, and offer in rare perfection the characteristic coast terraces ([Fig. 287] and [Fig. 278], [p. 250]). Midway between these two rising sections of the crust, and less than twenty-five miles distant from either, is the island of Santa Catalina, which has been sinking beneath the waves, and apparently at a similarly rapid rate ([Fig. 288]). The topography of the island shows the intricate detail of a maturely eroded surface, while that of the neighboring San Clemente shows only the widely spaced, deep cañons of the infantile stage of erosion ([Fig. 165] and [pl. 12 A]). While Santa Catalina has been sinking, San Pedro Hill has risen 1240 feet, and San Clemente, 1500 feet. It is characteristic of a sinking coast line that the cliff recession is abnormally rapid, and evidence for this is furnished by the shores of Santa Catalina, upon which the waves are cutting the cliffs back into the beds of cañons, and so causing small falls to develop at the cañon mouths.
Plate 12.
A. V-shaped cañon cut in an upland recently elevated from the sea, San Clemente Island, California (after W. S. Tangier-Smith).
B. A “hogback” at the base of the Bighorn Mountains, Wyoming (after Darton).
Fig. 288.—Map of Santa Catalina Island, California, showing the characteristic surface of an area which has long been above the waves, and the entire absence of coast terraces (after U. S. C. and G. S.).