Excerpt From “Shakopee: An Environmental History” by Kathryn Cravens
The land features seen in the Minnesota River Valley today are largely the result of glaciers that moved across the landscape for millions of years. During the Ice Age, which began about 2 million years ago, large sheets of ice (sometimes up to a mile in thickness) moved across North America. As the glaciers traveled, they picked up and carried with them rocks and soil. During warmer periods, when the glaciers melted and receded, they left behind these rocks, or glacial till. In some places this till is so thick that it forms hills. In other places, the rocks scattered across the landscape are reminders of the glaciers’ former presence
The bulk of Lake Agassiz juxtaposed with the modern Great Lakes and state/national boarders
Aside from the rocks left behind as glaciers melt, they also shaped the earth in other ways. The sheer weight and movement of the glaciers sculpts the earth into new land forms by creating hills and valleys. Minnesota, including Scott County, is a land of 10,00 lakes because of the glaciers. In many places, buried glacial ice eventually melted and left behind depressions in the earth that became filled with water to create the ponds, wetlands and lakes that define our state’s landscape.
Perhaps the most visible evidence of Scott County’s glacial heritage can be seen by drivers on Highway 169. In open areas, drivers can look to the north and see the bluff line on the other side of the river. Looking south they can see another bluff line. These bluffs mark the original banks of Glacial River Warren.
Glacial River Warren was a product of the last major era of glaciers, known as Wisconsinan Glaciation, which began about 100,000 years ago. About 12,000 years ago, the glaciers had melted significantly and this meltwater formed Lake Agassiz, an enormous body of water larger than all of today’s great lakes combined.
The Minnesota River- shown as a thin blue line above- inserted inside the approximate historical footprint of Glacial River Warren
Beginning around 11,500 years ago, for a time Lake Agassiz drained south through Glacial River Warren. Not surprisingly, a lake the size of Agassiz required an equally impressive outlet river, which is why the banks of Glacial River Warren were so far apart. The Minnesota River is a tiny stream in comparison to what would have been the raging waters of the Warren.
Approximately 8,500 years ago, the drainage form Lake Agassiz shifted back north to Hudson Bay. Today, the north-flowing Red River on the border between Minnesota and North Dakota is all that remains of the large drainage basin that was Lake Agassiz.
Hikers on the MN River Valley State Trail will see many seeps and springs trickling out from the base of the bluff. These springs are important water sources that made settlement and industry possible throughout Scott County.