The basement rocks of the Santa Lucia Range contain Mesozoic Franciscan and Salinian Block rocks. The Franciscan complex is composed of greywacke sandstone and greenstone, with serpentinite bodies and other Ultramafic rocks present. Small areas of marble and limestone lenses form resistant outcrops that are prominent landscape features, often white to light gray in color. The Salinian block is made up of highly fractured, and deeply weathered meta-sediments, especially biotite schist and gneiss, intruded by plutonic (granitic) rocks such as quartz diorite and granodiorite. Both formations have been disrupted and tectonically slivered by motion on the San Andreas and associated fault systems. The Palo Colorado and Church Creek faults are prominent features influencing the linear northwest–southeast alignment of primary drainages.