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It used to be that a misfit was a person who didn’t “fit” into the standard norms of society. Would you believe that “misfit” also applies to the Minnesota River? It doesn’t fit into the valley in which it flows. Let’s see why.

The Minnesota River begins at Big Stone Lake on the South Dakota border and flows 145 miles southeast to the Mankato area, where it makes a bend of a little more than 90 degrees and continues some 80 miles northeast to join the Mississippi River at nearby Fort Snelling.

The river and its tributaries drain an area of almost 17,000 square miles, mostly in the state of Minnesota, but also including parts of Iowa and South Dakota. Its drainage basin encompasses all or part of 39 Minnesota counties. Much of its water is contributed by tributaries which enter the river upstream from Mankato and which include smaller rivers like the Blue Earth, Cottonwood, Redwood, Yellow Medicine, Chippewa, Lac qui Parle, and Pomme de Terre.

The Minnesota flows through an enormous valley. At its height, it ranged from 1-5 miles wide and 75-100 ft. deep; yet,the river itself occupies just a small portion of this valley. Why is this the case? To answer this question we need some understanding of glaciers.

The Impact of Glaciation

North of Lake Traverse is a vast expanse of some of the flattest land on earth, known in part as the Red River Valley. Around the margins of this valley are sand and gravel ridges. These are interpreted to represent the shores of a vast ancient lake. This lake was called Glacial Lake Agassiz.

It collected the waters of melting glaciers for many centuries. At its largest, Lake Agassiz covered an area of 200,000 square miles. Its southern end was blocked by a highland natural dam.Then, thousands of years ago, this dam ruptured and through it poured the vast waters from this huge lake. A gigantic river called the Glacial River Warren was created. It was named after General G. K. Warren, who was the first to publish a theoretical description of it.

Radiocarbon dates suggest that this episode began about 12,000 years ago. Over time, the River Warren began its work of carving the Minnesota River Valley Some scholars, however, such as Carrie (Jennings) Patterson of the Minnesota Geological Survey, believe the erosional effects of the River Warren could have taken place during a cataclysmic event of a much shorter duration; creating the Valley in a matter of weeks or months.

Whatever the length of time involved, the River Warren aggressively cut its valley. As the melting ice receded,other outlets were formed, such as to the east, where Lake Agassiz drained into Lake Superior by way of Rainy Lake.

As these water diversions occurred, the River Warren shrank to its present size, which we now call the Minnesota River, leaving it a “misfit” in an immense valley as a reminder of what it once was.

Robert Douglas is a professor emeritus of Gustavus Adolphus College. He has been fascinated by the historical geography of this area for a long time. Reach him at bdouglas@gac.edu.

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