The volcanic series of Baja California is divided into two chemically different cycles.

A first calco-alkaline cycle is represented by deposits of highly pyroclastic andesites and dacites. This volcanism was most intense in the Miocene but started during the Oligocene. The andesitic series of Sinaloa is comparable in age to series in Baja California, but the imposing ignimbritic series of the Sierra Madre Occidental is not found at Baja California. Beginning in the Pliocene, an alkaline cycle was developed. This cycle is represented by large amounts of Hawiitan-type tuffs and is partly of Recent-Quaternary age. Some of these eruptions have occurred within historic time (Tres virgenes, close to St. Rosalia).

The chemical character of the lavas of Baja California is interpreted according to the pattern of geotectonic evolution which has been proposed for the west part of the Mexican continent, and specially in relation to the post-Pliocene opening phenomena of the Gulf of California.

A compilation of recent chemical data concerning the volcanism of Mexico was processed by computers. The program defined the petrochemical characteristics and a thesis is proposed on the petrogenetic interpretation of the three large volcanic provinces of Mexico: (1) the calco-alkaline trans-Mexican axis; (2) the calco-alkaline volcanism (alkaline at Baja California) of the Pacific Coast; and (3) the overall alkaline volcanism (with tholeiitic manifestation) of the Gulf of Mexico.

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