California Sea Grant College Program

California’s Central Valley has historically been the site of some of the largest expanses of riparian oak forests in all of North America. Many of these forests have since been cleared to exploit fertile floodplain soils for farming. Dams, water diversions, levees and other flood-control structures have further starved the landscape of river meanders, flooding and silt deposition, contributing to yet more habitat degradation. The cumulative result of human activity is that more than 95 percent of these historic riparian forests have been destroyed, and the only undammed river on the western slope of the Sierra Mountains is the Cosumnes.