Into the Cenozoic era, California was still very geologically active. The Coast and Transverse Mountains were created by the same geologic forces responsible for raising the Sierra Nevada during the Mesozoic. Sea levels rose and fell over time, so the state was home to a variety of ancient environments including shallow seas, estuaries and dry land. More than 2,300 species of Tertiary insects have been documented in the ancient tar deposits of California. Middle Eocene invertebrates of California included corals, gastropods, and pelecypods. At least some of these corals were solitary. Oligocene plant fossils include leaves, fruit and wood. During the Middle Miocene, Los Angeles County was home to a diverse fauna of marine invertebrates including many kinds of gastropods and pelecypods. Many of these fossils are very well preserved. Middle Miocene acorn barnacles were preserved in Santa Clara County. During the Late Miocene 18 inch long oysters lived in Contra Costa County. In Sonoma County freshwater gastropods and pelecypods were preserved. Sand dollars also inhabited California during the Late Miocene. California was home to aquatic mammals such as the dugongid Dusisiren and the desmostyle Paleoparadoxia during the Miocene. At the boundary between the Miocene and the Pliocene alder, cherry, Christmas berry, chumico, coffee berry, dogwood, elm, flannel bush, Catalina ironwood, California lilac, magnolia, mountain mahogany, manzanita, live oak, poplar, bush poppy, swamp cypress, sumac, desert sweet, sycamore, tupelo, and willow all grew around the San Francisco Bay Area.