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Geology of Turtle Mountain and Missouri Coteau

Missouri Coteau, Kidder County, ND.
Missouri Coteau, Kidder County, ND.

Have you ever noticed how the hilly topography of Turtle Mountain is much the same as the Missouri Coteau, that band of hills that runs along the north and east side of the Missouri River? If so, it is because they are the same geological landform — largely dead-ice "moraine," or collapsed glacial topography.

The Missouri Coteau is a band of glacial hills approximately thirty miles wide extending from southwestern Saskatchewan southeast to central North Dakota then southward through the Dakotas to about the Nebraska state line. It is bordered on the south and west by the Coteau Slope, a narrow band of land adjacent to the Missouri River that contains both glacial and erosional features. On the north and east it is bordered by the Glaciated Plains which has a more gently rolling topography and lies between two hundred and four hundred feet lower in elevation.

During the ice age, there were several advances and retreats of the glaciers through the Glaciated Plains which lies between the Missouri Coteau and the Red River Valley. What is now Turtle Mountain and the Missouri Coteau were bedrock highs, so as the glacier advanced it ran up against them.

As the glacier thinned toward the end of the ice age, shearing occurred around the base of what is now Turtle Mountain and Missouri Coteau. This resulted in lots of ice and ground up rock material (glacial till) being broken off, pushed up, and deposited on the two areas. Estimates are that there was several hundred feet of this mixture of ice and till. When the ice all melted, the slumping, and sliding of all that material produced a hummocky topography with an abundance of wetlands.

Where you can spot the Missouri Coteau

The margins of Turtle Mountains are easy to identify in most areas, but it can be more difficult for the Missouri Coteau. Here are a few spots to look:

  • It is quite distinct about 12 miles south of Harvey on Highway 3, when the highway heads up a steep escarpment that rises 400 feet within about a mile. That escarpment (The Missouri Escarpment) is the boundary between the Glaciated Plains and the higher Missouri Coteau.
  • Traveling Highway 5 between Crosby and Bowbells, the Missouri Coteau is the set of hills off to the south.
  • You can see the hills about 12 miles south of Minot on Highway 83, near the old radar installation.
  • The escarpment is quite prominent west of Forbes.
  • Traveling west from Jamestown on I-94, look for it near Windsor.
Chuck Lura has a broad knowledge of "Natural North Dakota"and loves sharing that knowledge with others. Since 2005, Chuck has written a weekly column, “Naturalist at Large,” for the Lake Metigoshe Mirror, and his “The Naturalist” columns appear in several other weekly North Dakota newspapers.
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