Streams in the southern part of California are small and intermittent.  Draining the western slopes of the Sierra Nevada, however, is a series of streams of varying size.  In the north the Pit River and the Sacramento River combine to flow the length of the Sacramento Valley, through the Delta area, into San Francisco Bay.  At intervals along the way other streams empty their waters into the Sacramento.  Some of these are the Feather, Yuba, Bead, and American—streams of considerable size—along with a host of lesser creeks that drain small watersheds.

South of the Delta lies the San Joaquin Valley.  Streams coming from the mountains into the northern two-thirds of the San Joaquin Valley empty into the San Joaquin River and drain northward to join the Sacramento just before emptying into San Francisco Bay.  In the southern one-third of the Valley, streams have no natural drainage to the ocean, but empty into Tulare and Buena Vista Lakes.

Most of the major streams are fed by melting snow from the high slopes of the Sierra Nevada.  Streamflow continues well into or throughout the arid summer months.  Many of the streams have been dammed to hold the water supply in reservoirs for irrigation, industrial, and domestic uses thoughout the dry part of the year, and to provide flood control during the winter and spring.  As a result, less and less water from these streams flows directly to the ocean.  Most of it is being used at least once before being drained to the sea or percolated into underground storage.