Time zones in the Dakotas and Nebraska

North Dakota's mountain counties are the ones west of the Missouri and Yellowstone line in 49 CFR 71.7(a), with a later bend along Mercer, Morton, and Sioux counties. Sioux County is explicitly split: the line follows State Highway 31. Dunn and McKenzie counties also come back split in the boundary sample because the river runs through them.

South Dakota leaves the river near Pierre. Stanley County, across from Pierre, is mostly Mountain Time with a Central share in the sample. The counties west of Jones, Mellette, and Todd are mountain; those three counties are on the central side of their western borders.

Nebraska's panhandle is Mountain Time. The legal line then wanders by section until it reaches the west lines of Thomas, McPherson, Lincoln, Hayes, and Hitchcock counties. Cherry County is split in the sample, which fits a line that crosses the county instead of following its border.