This raster data set represents the saturated thickness of the High Plains aquifer of the United States, 2009, in feet. The High Plains aquifer underlies approximately 112.6 million acres (176,000 square miles) in parts of eight States: Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming. The aquifer's saturated thickness ranges from near zero to about 1,200 feet (Weeks and Gutentag, 1981). Water-level declines occurred in parts of the High Plains aquifer soon after the onset of substantial irrigation with groundwater (about 1950) (Luckey and others, 1981). This data set was generated in ESRI ArcInfo Workstation Version 9.3, which is a geographic information system (GIS), using an aquifer base raster data set, saturated-thickness data from wells measured in 2009 and from some additional wells in New Mexico, which were measured in 2005 through 2008, and a published map of the aquifer's saturated thickness in 1980 (Weeks and Gutentag, 1981). For this data set, (1) areas that Gutentag and others (1984) delineated as areas of "little or no saturated thickness" and (2) areas, generally near the aquifer boundary, with interpolated saturated thickness less than zero were set to a saturated thickness of 10 feet. REFERENCES CITED -- Gutentag, E.D., Heimes, F.J., Krothe, N.C., Luckey, R.R., and Weeks, J.B., 1984, Geohydrology of the High Plains aquifer in parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming: U.S. Geological Survey Professional Paper 1400-B, 63 p. Luckey, R.R., Gutentag, E.D., and Weeks, J.B., 1981, Water-level and saturated-thickness changes, predevelopment to 1980, in the High Plains aquifer in parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming: U.S. Geological Survey Hydrologic Investigations Atlas HA-652, 2 sheets, scale 1:2,500,000. Weeks, J.B., and Gutentag, E.D., 1981, Bedrock geology, altitude of base, and 1980 saturated thickness of the High Plains aquifer in parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming: U.S. Geological Survey Hydrologic Investigations Atlas HA-648, 2 sheets, scale 1:2,500,000.