Matthews (1976) has presented evidence regarding the petrographic similarity of volcanic rocks on opposite sides of the San Andreas fault in the central California Coast Ranges. I will not discuss the petrographic aspects of the paper. My discussion focuses on his conclusions regarding the Chalone Creek fault.

Matthews (1976) concluded that the Chalone Creek fault continues southeasterly and becomes the “Peachtree fault” with an overall length of 80 to 85 km. He further suggested that this long fault may have been an early Miocene precursor of the San Andreas fault, dividing granitic basement on the west from unspecified...

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