V. L. McGuire 2007 The High Plains aquifer underlies 111.4 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 extensive ground-water irrigation. This report presents water-level changes in the High Plains aquifer from the time prior to substantial ground-water irrigation development (about 1950) to 2005 and from 2003 to 2005. Water-level changes from predevelopment to 2005 ranged between a rise of 84 feet and a decline of 277 feet. Area-weighted, average water-level change in the aquifer was a decline of 12.8 feet from predevelopment to 2005, a decline of 0.8 foot from 2003 to 2004, and a decline of 0.2 foot from 2004 to 2005. Total water in storage in the aquifer in 2005 was about 2,925 million acre-feet, which was a decline of about 253 million acre-feet (or 9 percent) since predevelopment. application/pdf 10.3133/sir20065324 en Water-Level Changes in the High Plains Aquifer, Predevelopment to 2005 and 2003 to 2005 reports