This report contains digital data and accompanying documentation for boundaries of areas of little or no saturated thickness within the High Plains aquifer in parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming. This digital data set was compiled from a digital coverage that was created for publication of paper maps in McGrath and Dugan (1993, Water-level changes in the High Plains aquifer -- predevelopment to 1991: U.S. Geological Survey Water-Resources Investigations Report 93-4088, 53 p.) The data are not intended for use at scales larger than 1:1,000,000.