The High Plains aquifer extends from approximately 32 to 44 degrees north latitude and from 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 water-level measurements from wells screened in the High Plains aquifer and measured in both predevelopment (about 1950) and for 2017. There were 2,928 wells measured in both predevelopment (about 1950) and 2017 as well as 63 wells located in New Mexico, which were measured in predevelopment and at least once between 2013 and 2016. These water-level measurements were used to map water-level changes, predevelopment (about 1950) to 2017. The map was reviewed for consistency with the relevant data at a scale of 1:1,000,000.