Study of the distribution of corals and rock types in the Mission Canyon Limestone and the lower part of the Charles Formation (Tilston, Frobisher-Alida, and Ratcliffe intervals) in 29 cores from wells in the Williston basin of western North Dakota resulted in recognition of four coral zonules and three regressive carbonate cycles. Although coral diversity and abundance decrease eastward toward the basin margin and upward in the sequence because of the influence of increasingly restricted environments, two of the zonules in the lower part of the Mission Canyon extend into areas of western North Dakota where marker-defined intervals are difficult or impossible to recognize. The Nesson anticline, or a paleotopographic ridge following the same trend, may have been a barrier hat hindered coral development in the east during later Madison deposition. Parallelism between the zonules and marker beds used to define standard intervals employed in subsurface stratigraphic correlation indicated that the marker beds are essentially time lines within the area studied. The first records of Stelechophyllum micrum and S. banffense in Madison rocks in the United States indicate a connection with the Alberta shelf and indicate that North Dakota was probably a part of the Central Western Interior subprovince during Osagean time.

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