The Diablo Range is one of the northwest-trending central Coast Ranges of California. It is a complexly-faulted, asymmetrical anticlinorium structurally bounded on the west by the San Andreas fault and on the east by the San Joaquin Valley. Its core consists of the Late Jurassic Franciscan Formation and intruding serpentine. These rocks were formed in an extremely deep and narrow eugeosynclinal trough directly on a simatic base. Younger, flanking rocks, locally overturned, are of Early Cretaceous to late Pliocene age. Core rocks crop out (1) as faulted slivers in the San Andreas fault zone and (2) as piercements along the crest of the principal anticlinal axis.

A major diastrophic episode closed the Jurassic period, broad folding took place late in the Cretaceous, and local uplift occurred in late Miocene time. The piercements transected rocks of the anticlinal crest in late Pliocene and early Pleistocene time.

The diapiric structures are the result of intense compression of a thick sedimentary wedge, accompanied by great vertical movements in a series of intermittent orogenies. Sheared serpentine played an important part in final emplacement. In the broad view, these structures are but detail in the great fault features of western California which developed at the continental margin while faulting, folding, and intrusion took place during thrusting of the simatic sea-floor sea-floor materials under the sialic edge of the continent.

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