undifferentiated rock units

Paleontology and geology

Because much of western California was underwater during the Tertiary, marine deposits occur throughout the state. Marine sandstones and shales were alternately deposited and then eroded as sea levels changed. These marine rocks contain a diverse fauna of corals, bivalves, gastropods, scaphopods (tusk shells), echinoderms, and foraminifera (single-celled protists with shells). Although deposits from river channels, floodplains, and deltas can be found in northern counties, terrestrial sediments are more common in the south. The floras of these deposits indicate that the climate became less tropical and more temperate throughout most of the Tertiary. Increased tectonic activity in the Late Tertiary uplifted the Coast and Transverse Ranges, eliminated the inland sea that had filled the Central Valley, and generated widespread volcanism. California’s grasslands were filled with herbivores and carnivores.