Until the development of the major state and federal water projects that began delivering surface water to the area in the second half of the 20th century, the Central Valley relied almost exclusively on groundwater. Heavy pumping of groundwater has led to significant land subsidence throughout the valley, causing major damage in some areas to canals, aqueducts, and other infrastructure. This subsidence was particularly pronounced in the valley’s southern half, which is known as the San Joaquin Valley. By 1970, approximately half the San Joaquin Valley, or roughly 5,200 sq mi, had subsided by at least 1 ft, according to the website of the U.S. Geological Survey. Some locations had subsided by as much as 28 ft.