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In the southern Santa Anas and throughout most of California’s share of the Peninsular Ranges, this granitic rock is now well exposed. In the northern Santa Anas, however, its distribution is less extensive. The highest peaks in the range, Santiago and Modjeska Peaks (together called Old Saddleback), are still covered by older, overlying metamorphic rocks.

The granitic rocks are still rising, more than offsetting the leveling effects of erosion. Thus, although the rocks of the Santa Ana Mountains range between old and ancient, the origin of the range itself as a structural unit is quite recent.

Of more than casual interest to Orange Countians is the fact that for at least the past 10 million years, the Peninsular Ranges province (along with the present Los Angeles Basin and a wedge of coastal central California) has been drifting northwest relative to the rest of the North American continent. In a global view, this motion is seen as a lateral sliding (or rather a repeated lurching) at the interface between the largely oceanic Pacific Plate and the largely continental North American Plate. The average rate of movement in the early 21st century is about 2 inches per year—enough, if it continues, to put Orange County abreast of San Francisco 12 million years from now.