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The Ice Age

How this land was sculptured by glaciers

When driving through upper Midwest, one is surrounded by the physical features created by the huge glaciers that covered this area until about 12,000 years ago; it is easy to be unaware of the unique characteristics across the landscape which resulted from these mountainous ice sheets sluggishly moving southward from Canada. The glaciers covered almost all of Wisconsin, Minnesota, the eastern half of the Dakotas, and some areas of northern Iowa and Nebraska.

Three major ice age features in this area that can give one an idea of the enormous impact of the glaciers are: the Minnesota River Valley, the Coteau des Prairies in eastern South Dakota, and the Driftless Area in Wisconsin. Today the Minnesota River is a tree-lined, modestly sized, gentle waterway flowing from Ortonville, Minnesota to Mankato; there it takes a sharp left -hand turn toward the Twin Cities and empties into the Mississippi River.

Twelve thousand years ago it was a gigantic torrent draining Lake Agassiz. Melting glacial water had created Lake Agassiz, which extended from the area of Big Stone Lake in northeastern South Dakota to the northern part of Manitoba. It was massive, larger than all the current Great Lakes combined.

One may pause along any spot that allows a good view of the Minnesota River Valley and try to visualize the astounding sight of this flowing river. For example, if one is approaching Montevideo, Minnesota on US Hwy 212, pull over, and look across the valley; imagine the entire valley completely full of brown, cascading water roaring south. It is estimated that the flow of water exceeded the total combined volume of present-day Mississippi, Nile, and Amazon rivers. This out-flows continued for over a thousand years.

The Coteau des Prairie is line of rolling hills and highlands extending from the southern border of North Dakota to southern South Dakota, and then extending slightly into western Minnesota and northern Iowa. The Coteau is a direct result of earth, rocks, sand, and mixed soils being pushed and shoved by intermittent glacial lobes resulting in a ridge of deposits 200 miles long and 100 miles wide. These low lying hills are covered by centuries-old grasslands occasionally interspersed with farmland. They are bisected with tree-lined gullies and gulches and sprinkled with thousands of small lakes, slews, and kettle holes. In many areas rocks from the size of marbles to car bodies are eroded out of the soil and exposed to the sun. The result is a virtual showplace of the ancient glaciers at work.

One of the better places to view the Coteau is just east of Sisseton, South Dakota along SD Hwy 10. The hills rise rather steeply here and provide a good sense of the elevation differential between the Minnesota Valley to the east and the rising ridge of glacial deposits to the west. Another good viewing spot is at Crandall, South Dakota; it is here that the Coteau reaches its westernmost point and the rise from the prairie flatlands to top of the ridge of hills is quite pronounced. When viewing these hills, try to imagine that the upper surface of the ice sheet was two or three times as high as the uppermost reaches of these hills. (It is estimated that the ice was 10,000 feet thick in northern Canada.)

Southwestern Wisconsin has a different history with regard to the glaciers; they never got there, or at least, the ice detoured its way around the region. It is called the Driftless Area for its lack of glacial deposits, or “drift.” The geology is radically different from the surrounding glaciated terrain. The area is characterized by exposed bedrock, severe river erosion, springs, caves, sinkholes, and disappearing streams. The Wisconsin Dells are a noteworthy example of the Driftless Area. A good place to headquarter when meandering around this area is Lancaster Minnesota; the Grant County Courthouse is worth a look before you begin exploring the countryside.

Also see: The Pumps Station at Crandall, South Dakota near the Coteau hills.

Mainstreetmoments.com believes that travel pleasures can be greatly enhanced when one is aware of the surrounding countryside; we aim to bring you bits of information and encouragement that will activate your curiosity when traveling. As always, we welcome your suggestions!

Author: EVM STAFF on 03/23 2008
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Posted by: Anonymous on April 12 2008
I love the article about the glaciers. I find that part of South Dakota history very fascinating. I would like to learn more. Gretchen Hagin Long Beach, CA
Posted by: Anonymous on March 23 2008
What a wonderful article. Thank you for this. We travel often from South Dakota to Minneapolis. I'm looking forward to my next trip.

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