A pre-mid Cretaceous sequence of sandstones, shales, limestones, and probable tuffs were first intruded by a granite pluton. Dacite and andesite dikes then intruded the pluton and the surrounding strata, and reached the surface as flows. Regional metamorphism was tnen imposed upon these rocks. Next a granodiorite pluton was emplaced, producing a contact metamorphic aureole with a width of about 2000 feet. The intrusion of aplite and pegmatite dikes followed the granodiorite emplacement. Many of the streams in the area follow faults and fractures. The northwest trending normal faults follow regionaltrends, and give a linear character to many valleys. Where cutting metamorphic and plutonic contacts, the Calabazas Fault shows right lateral offset, and the Vallecitos Fault shows left lateral offset. A locally derived coarse boulder conglomerate rests on a high relief unconformity. This is overlain by a more mature cobble conglomerate of &,cene (?) age.
