Potentiometric-surface map of water in the Fox Hills-Lower Hell Creek aquifer in the Northern Great Plains area of Montana

The potentiometric surface of water in the Upper Cretaceous Fox Hills-lower Hell Creek aquifer is shown on a base map at a scale of 1:1,000,000. The map is one of a series produced as part of regional study of aquifers of Cenozoic and Mesozoic age in the northern Great Plains of Montana. The contour interval is 100 feet. The map shows that the direction of regional ground-water movement is toward the northeast. Recharge occurs on the flanks of the Black Hills uplift, the Cedar Creek anticline, the southwest part of the Bull Mountains basin, and on the out-crop areas. Discharge from the aquifer occurs along a short reach of the Yellowstone River. The average discharge from 335 wells is about 16 gallons per minute and the specific capacity of 185 wells averages 0.49 gallon per minute per foot of drawdown. (USGS)