The Cosumnes River is a river in northern California in the United States. It rises on the western slopes of the Sierra Nevada and flows approximately 52.5 miles (84.5 km) through the Central Valley, emptying into the Mokelumne River in the Sacramento-San Joaquin Delta.
The Cosumnes is one of the few rivers in the western Sierra without major dams. The Cosumnes River Preserve, managed by The Nature Conservancy, is located just upstream from the Delta. Towns and cities along the Cosumnes River include Plymouth, Rancho Murieta, Sloughhouse, Wilton, Elk Grove, and Galt.
