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 dataset contains water-level measurements from wells screened in the High Plains aquifer and measured in both predevelopment (about 1950) and for 2019. There were 2,741 wells measured in both predevelopment (about 1950) and 2019 as well as 71 wells located in New Mexico, which were measured in predevelopment and at least once between 2015 and 2018. These water-level measurements were used to map water-level changes, predevelopment (about 1950) to 2019. The map was reviewed for consistency with the relevant data at a scale of 1:1,000,000.