A Study of Miocene Vulcanism in Southern California

• Main Author: Bonillas, Ygnacio, III
• Format: Others
• Published: 1935
• Online Access: https://thesis.library.caltech.edu/5513/1/Bonillas_y_1935.pdf; Bonillas, Ygnacio, III (1935) A Study of Miocene Vulcanism in Southern California. Master's thesis, California Institute of Technology. doi:10.7907/BZRE-N110. https://resolver.caltech.edu/CaltechTHESIS:01122010-091637518 <https://resolver.caltech.edu/CaltechTHESIS:01122010-091637518>

The widespread Miocene volcanic rocks of Southern California represent at least four distinct epochs of activity. Lower Miocene vulcanism is represented by the basic hypersthene andesite flows north of Soledad Canyon and east of Mint Canyon. Lower middle Miocene flows are found in the Santa Monica Mountains and the Verdugo Hills; they are olivine poor basalts. Upper middle Miocene intrusives are abundant in the Santa Monica Mountains; they are usually olivine rich basalts. Upper Miocene siliceous andesite and dacite flows occur in the San Jose Hills. It is found that the distinction between the lower, middle, and upper Miocene volcanics is sharp, but that the two epochs of middle Miocene vulcanism resulted in quite similar rooks. The latter rocks are the most abundant in this region, and volcanics of lower or upper Miocene age are rare.