principal water-conveyance structure of the California State Water Project, U.S. From the Sacramento River delta east of San Francisco, it runs south through the San Joaquin Valley and over the summit of the Tehachapi Mountains, a distance of 273 miles (440 km). At this point it divides into east and west branches, the former terminating some 444 miles (715 km) from the delta. The aqueduct is the world's largest water-conveyance system, comprising more than 20 pumping stations, 130 hydroelectric plants, and more than 100 dams and flow-control structures. Channel sizes vary along the aqueduct, a typical section being a concrete-lined canal 40 feet (12 metres) wide at the base, with 30 feet (9 metres) the average depth of flow. The California State Water Project, begun in 1960, is designed to yield millions of acre-feet of water annually to southern California from sources in the northern portion of the state.