Parts of the United States are sinking according to recent reports by the U.S. Geological Survey (USGS). A USGS report (‘Land Subsidence in the San Joaquin Valley, California, as of 1972,’ U.S. Geol. Surv. Prof. Pap. 437-H) prepared in cooperation with the California Department of Water Resources states that at least 4300 mi2 of the economically important San Joaquin Valley of California have subsided more than a foot since the 1920's. This has created the largest area of intense land subsidence in the world.
About 5200 mi2 of the San Joaquin Valley have been affected by subsidence, and the valleywide volume of subsidence amounts to about 15.6×106 ac ft, or about half the volume of Great Salt Lake. This represents one of the largest environmental changes imposed by man.