BLOG: The Dangers Of Land Subsidence From California’s Groundwater Overdraft

Land subsidence from overpumping groundwater in the San Joaquin Valley has been called the largest human alteration of the Earth’s surface. When the last comprehensive surveys were made in 1970, subsidence in excess of one foot had occurred over more than 5,200 square miles (13,000 sq km) of irrigable land – half the entire valley. Southwest of Mendota, a town that prides itself on being the cantaloupe center of the world, maximum subsidence was estimated at 28 feet (8.5m). By this time, however, massive infusions of surface water were being delivered to the valley, and subsidence was slowing or had been “arrested.”