GEOLOGIC FORMATIONS [c3, p63]

On its path through nearly the length of California, the San Andreas fault separates major crustal blocks (Figure. 3.3). In much of northern and central California, the fault is a southeast-trending boundary between the Salinian block of granitic and metamorphic rocks on the west and the Franciscan assemblage and overlying strata of the Great Valley sequence on the east. In its southerly course the fault abruptly curves eastward to cut diagonally across the Transverse Ranges, and then splays into several auxiliary faults before the main strand terminates near the Gulf of California. In southern California the basement rocks cut by the San Andreas fault are mostly Precambrian and younger metamorphic and plutonic rocks, and the crustal blocks on either side of the fault generally do not show the distinctive lithologic contrast that is so striking in central and northern California.