ABSTRACT: Interpretive Structural Cross Section from the Central Diablo Range to the San Joaquin Valley, California
ERSKINE, M. C., Consulting Geologist, El Cerrito, CA
The Central Diablo Range is an antiform cored with rocks of the Franciscan Complex that lies between the San Andreas fault on the west and the central San Joaquin Valley on the east. This Franciscan core is everywhere separated from the coeval, tectonically-overlying sedimentary rocks of the Jurassic and Cretaceous Great Valley Sequence (GVS) by a complex fault zone, and in many places by the mafic rocks and serpentines of the Coast Range Ophiolite. Recognition that the Franciscan rocks and the GVS are essentially coeval and that the contact between them is a similar fault zone for more than 500 km along the west side of the Great Valley of California led Bailey and others to interpret this fault zone as a thrust fault, often referred to as the Coast Range Thrust.
Because the leading edge of thrusting does not crop out in the Great Valley, it generally has been assumed that this thrust fault verges westward. However, recent interpretations of the Coalinga May 2, 1983, earthquake have suggested that in the Coalinga area at least, the anticlines are a result of east-verging blind thrusts. New geophysical data at Garzas Creek in the Central Diablo Range have suggested that the Central Diablo Range may be interpreted in terms of this east-verging paradigm. A balanced cross section shows east vergence that extends from the Central Diablo Range to the center of the San Joaquin Valley along Garzas Creek.