Nine major and minor chemical elements and specific gravity have been determined for composite samples from 542 localities in Cretaceous batholithic rocks of southern California. The rocks range from gabbro to quartz monzonite. Chemical variations reflect the strong petrographic zonation of the region from abundant low-silica rocks near the continental margin to abundant high-silica rocks inland 100 to 150 km. The rocks are mostly quartz plutonites, and within each quartz plutonite group, most chemical variations are opposite those of the batholith as a whole; potassium, however, increases consistently inland. The variation of K cannot be correlated with the variation of any other major or minor element of the batholithic rocks in any of the rock types except gabbro. Though field relations and radiometric ages prove that the gabbroic rocks belong to the batholith, their magmatic origins appear to be separate from those of the intermediate- and high-silica rocks.