V. L. McGuire 2009 The High Plains aquifer underlies 111.6 million acres (174,000 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 ground water in the aquifer area. This report presents water-level changes in the High Plains aquifer from the time before substantial ground-water irrigation development had occurred (about 1950 and termed 'predevelopment' in this report) to 2007, from 2005-06, and from 2006-07. The report also presents the percentage change in saturated thickness of the aquifer, from predevelopment to 2007. Measured water-level changes from predevelopment to 2007 ranged from a rise of 84 feet in Nebraska to a decline of 234 feet in Texas. The area-weighted, average water-level changes in the aquifer were a decline of 14.0 feet from predevelopment to 2007, a decline of 0.4 foot during 2005-06, and a decline of 0.6 foot during 2006-07. Total water in storage in the aquifer in 2007 was about 2.9 billion acre-feet, which was a decline of about 270 million acre-feet since predevelopment. application/pdf 10.3133/sir20095019 en U.S. Geological Survey Water-Level Changes in the High Plains Aquifer, Predevelopment to 2007, 2005-06, and 2006-07 reports