The rock of the Santa Lucias is dominated by granitic basement of the Salinian Block, between the San Andreas Fault and Sur-Nacimiento Fault. The core of the Salinian block formed as part of the same batholith which forms the core of the Sierra Nevada Mountains and the Peninsular Ranges of Baja California. It was separated from the North American Plate and transported north by the action of the San Andreas Fault from an original position. It is predominantly Mesozoic granitic and pre-Cretaceous metamorphic rocks. There is some Cretaceous sedimentary rock of the Great Valley Sequence, considerable Miocene marine sediments, and some other Cenozoic sediments. Units west of the Sur-Nacimiento Fault are dominated by rocks of the Franciscan Assemblage.