V. L. McGuire 2011 The High Plains aquifer underlies 111.8 million acres (175,000 square miles) in parts of eight States - Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming. Water-level declines began in parts of the High Plains aquifer soon after the beginning of substantial irrigation with groundwater in the aquifer area. This report presents water-level changes in the High Plains aquifer from the time before substantial groundwater irrigation development had occurred (about 1950 and termed "predevelopment" in this report) to 2009, from 2007-08, and from 2008-09. The report also presents change in water in storage in the aquifer, from predevelopment to 2009. Ninety-nine percent of the water-level changes from predevelopment to 2009 ranged from a rise of 41 feet to a decline of 178 feet. The area-weighted, average water-level changes in the aquifer were a decline of 14.0 feet from predevelopment to 2009, a decline of 0.1 foot from 2007-08, and a decline of 0.3 foot from 2008-09. Total water in storage in the aquifer in 2009 was about 2.9 billion acre-feet, which was a decline of about 274 million acre-feet since predevelopment. application/pdf 10.3133/sir20115089 en U.S. Geological Survey Water-level changes in the High Plains aquifer, predevelopment to 2009, 2007-08, and 2008-09, and change in water in storage, predevelopment to 2009 reports