Between the two of them, the Sacramento and the San Joaquin Rivers drain most of the state of California, collecting and concentrating rainfall and snowmelt form the Sierra Nevada and funneling it toward San Francisco Bay.

On the western side of the great Central Valley in northern California, the two rivers flow together into an inverted delta before heading westward into the bay. An inverted delta is the name geologists give to river deltas in which the braiding and branching out of the river channel occurs inland, before the river actually reaches the large body of water toward which it flows.