FIGURE 3.12.-Sequential diagrams showing plate-tectonic evolution of the San Andreas transform fault system (modified from Dickinson, 1981). Note that early transform faulting was west of the present-day San Andreas fault and presumably separated young oceanic rocks of the Pacific plate from rocks of the North American plate. Over time, the transform faulting has stepped eastward, and so virtually all the presently most active element, the present-day San Andreas fault, is now in rocks of North American plate aspect. In earlier diagrams, partial outline of the Gulf of California, which did not exist before 5 Ma, is shown for reference only.