The High Plains aquifer extends from south of about 32 degrees to almost 44 degrees north latitude and from about 96 degrees 30 minutes to 106 degrees west longitude. The aquifer underlies about 175,000 square miles in parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming. This digital data set contains the water-level measurements from 3,092 wells measured in both predevelopment (about 1950) and 2015 and from 72 wells, which are located in New Mexico and Wyoming and were measured in predevelopment and at least one time from 2011 to 2014. These water-level measurements were used to map water-level changes, predevelopment (about 1950) to 2015. The map was reviewed for consistency with the relevant data at a scale of 1:1,000,000.