Abstract

Two strata of Miocene San Onofre breccias, interbedded with Conejo volcanics, crop out on Anacapa Island, California (34 degrees 00'30"N- 119 degrees 19'27"W). The sedimentary breccias are composed of blocks and angular cobbles and pebbles of glaucophane schists, hornblende schists, chloritic and talcose schists, and pink quartzites surrounded by a sandy to silty matrix of metamorphic minerals and rock fragments. Intercalcated with the breccias are pink and light green silty sandstones composed of mineral and rock fragments common to the coarser breccia beds. Both breccia units have maximum thickness of about 35-40 ft. and dip between 5 degrees and 15 degrees N. Where extrusive rocks overlie the breccia units, a baked or altered zone a few centimeters thick exists at the contact of the 2 lithologic units. Inclusions of contorted shales are abundant in the extrusive rocks between the breccia units. Exposures of San Onofre breccia have been recognized near Point Dume, 35 mi. E of Anacapa Island and on Santa Cruz Island, about 4 mi. W.

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