More than one hundred bivalve species are recognized in the thick, predominantly pyroclastic, northwestern Baja California section which includes rocks and fossil localities cited in the original description of the Alisitos formation. A majority of the species is new.

Bivalves and associated fossils suggest an Aptian age for most and possibly for all of the section investigated. The environments of deposition were generally sublittoral, including widely distributed reefs of corals and pachydont pelecypods. Highest parts of the Alisitos formation in the type area were deposited in fresh water.

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