ABSTRACTThe Pliocene Ogallala Formation and the Quaternary Sand Hills Formation cover an extensive area in the north‐central prairie states. The area studied in this investigation includes only that portion between the Little White River, South Dakota, and the Niobrara River, Nebraska, where the saturated thickness is about 100 feet and a five‐day aquifer test showed that the coefficient of permeability is 439 gpd/ft2. The water has a total dissolved solids content of only 90 ppm. An average of 18 inches of precipitation falls on this arid country annually, and the average annual recharge to these permeable deposits is calculated at 2 to 3 inches.Little ground‐water development has occurred in the area to date, but the aquifer has considerable potential. The aquifer is exceptionally permeable, close to the surface and easy to drill, and has exceptionally good recharge and good quality water. Data on recharge rates and theoretical distance‐drawdown curves support the conclusion that irrigation of more than 1 quarter‐section for every 2 sections of land would cause a depletion of th