Prairie Coteau

What is that big hill you climb on interstate 29 when traveling southward near the South Dakota State line? I was asked that question recently, and as you students of geology certainly know, it is the Prairie Coteau.

The Prairie Coteau represents what was, before the last glaciation, a natural bedrock high over a small portion of southeastern North Dakota, with most lying in eastern South Dakota and adjacent Minnesota. Then, toward the end of the last ice age, as the glacier advanced southward and came into contact with the bedrock high, it split to form two lobes. One lobe, the Des Moines Lobe, was forced southeastward while the other lobe, the James Lobe headed southwestward.

As you head south on I 29 as you approach the state line, the escarpment to the Prairie Coteau is quite prominent, particularly to the west. The northern terminus of the escarpment is just east of Havana, North Dakota. To the west from there it trends rather sharply southward to the state line, however it is portion of the escarpment that trends southeastward from near Havana that is so prominent for travelers on I 29.

In this area the Prairie Coteau lies perhaps 500 or 600 feet above the surrounding plain and has several hundred feet of glacial drift. The landform of the coteau is often called dead-ice moraine, stagnation moraine, or more recently hummocky collapsed glacial topography. It is characterized by a very rolling landscape with lots of prairie potholes and no integrated drainage system.

Some of you may be wondering how the Prairie Coteau compares to the Missouri Coteau. They are the same type of landform, formed, of course, in a similar fashion. The same is true for the Turtle Mountains.

The Prairie Coteau is an interesting landform. The next time you travel this area take a good look at all the changes that occur as you drive out of glacial Lake Agassiz and up onto the Prairie Coteau. It is not just elevation that changes. Topography changes, soils change, the native vegetation changes, and the crops change. There are not many places where you can observe so much change in so short a distance, so don’t miss it.

Chuck Lura

Natural North Dakota is supported by NDSU Central Grasslands Research Extension Center and Minot State University-Bottineau, and by the members of Prairie Public. Thanks to Sunny 101.9 in Bottineau for their recording services.