FIGURE 3.3.-Geologic sketch map of California, showing distribution of principal basement rocks. Cenozoic cover not shown except for the Modoc Plateau, northeastern Sierra Nevada, Great Valley, and Santa Barbara-Ventura Basin. Based on U.S. Geological Survey (1966), Jennings and others (1977), and Ross (1934). Units: 1, Quaternary alluvium-shown only in Great Valley; 3, Cenozoic volcanic rocks of the Modoc Plateau; 4, Great Valley sequence-Lower Jurassic to Upper Cretaceous strata, including Coast Range ophiolite at base; 5, Franciscan assemblage of Lower Jurassic to Tertiary oceanic rocks; 6, Sierra Nevada batholith-dominantly Cretaceous granitic rocks; 7, Sierra Nevada metamorphic belt-early Paleozoic to Late Jurassic rocks, including fragments of ophiolites, island arcs, and melanges, intruded by Mesozoic plutons; 8, Klamath Mountains-early Paleozoic to Late Jurassic ophiolites, island arcs, and melanges, intruded by early Paleozoic to Cretaceous plutons.