Geology and ground water resources of Eddy and Foster Counties, North Dakota

Eddy and Foster Counties are in east-central North Dakota, high on the eastern flank of the Williston Basin. They are underlain by 3200 to 4300 feet of Paleozoic and Mesozoic rocks that dip gently to the west. The uppermost formation, the Cretaceous Pierre Shale, lies directly beneath the glacial drift and crops out in the valleys of the James and Sheyenne Rivers. Glacial drift that covers the entire are a averages about 150 feet thick but in certain buried valleys it is as much as 400 feet thick.