Cretaceous sediments have been known in the Williston Basin since the Lewis and Clark Expedition of 1804-1806. Many workers have contributed to the classification and correlation of these beds.

One problem has been the correlation of the Dakota and Fall River sandstones in the southern end of the basin. Samples and electric logs of wells drilled in central South Dakota within the last few years have clarified the relationship. The Skull Creek shale, the lowest formation of the Graneros group, may be traced eastward into the east-central part of South Dakota. The Fall River may also be traced to the central part of the state, where it has previously been correlated as a Jurassic or older sandstone. The true Dakota overlies the Skull Creek shale in the same area. It may be traced westward to the west-central part of the state, where it interfingers and wedges out into the middle part of the Graneros shales. The interval between the top of the Dakota and the top of the Fall Riv r sandstone ranges between 430 and 500 feet where both can be recognized.

Several Cretaceous sandstones produce oil or gas in areas adjacent to the Williston Basin. After consideration of their distribution within the Dakotas and eastern Montana, several areas are suggested for prospecting.