Ed. Note. This article was submitted by Eldridge Moores and Loren A. Raymond (University of California, Davis) for the author who was a student in the Department of Geology, University of California, Davis, at the time of his death in September 1969.
Franciscan rocks exposed in the Occidental-Guerneville area comprise three northwest-trending, northeast-dipping, fault-bounded units. The western unit contains semicontinuous, boudinaged, and sheared layers of graywacke sandstone, shale, chert, metachert, volcanic rock, metavolcanic rock, and glaucophane and related schists. Disrupted bedding generally dips northeastward. The middle unit forms a 400- to 4,000-m-thick zone of pervasively sheared shale containing masses of graywacke and metagraywacke sandstone, ultramafic rock, basic volcanic and metavolcanic rock, minor quartz diorite, tuffaceous siltstone and sandstone, chert, glaucophane and related schists, and Jurassic Knoxville-like shale. The eastern unit contains complexly deformed, unmetamorphosed, massive to thin-bedded graywacke sandstone, siltstone, shale, and rare chert. Sandstone from these three units differs in average, range and cumulative frequency of K-feldspar, as well as in mean quartz, plagioclase, matrix, and chert-lithic fragment content.