Two millon years ago Minnesota and the northern hemisphere of the Earth cooled for some unknown reason. Present-day Canada was subjected to a large amount of snowfalls. Because of the cooler environment, these snowfalls did not melt away year after year, but became compacted over time forming into large ice flows called glaciers. This Pleistocene Ice Age became the main source of constructional topography for current day Minnesota. The glaciers that moved over the land had a compactional force of 150 tons per square foot, being two miles thick in some places. Advancing 200 feet a year, they were slowed only by mild summers in their many stages of retreat and advance over the last two million years. These glaciers moved into prehistoric Minnesota to scrape areas clean of topsoil pushing boulders and debris many miles from their origin, sometimes leaving behind pulverized rock flour called loess. Eventually, this glaciation covered all of northern North America, pushing a little farther south into the center of the continent into Missouri and Illinois. Only a small "driftless" area in Minnesota existed in and adjacent to south-eastern Minnesota, where the glaciation was turned away near Winona and La Crosse, Wisconsin, which today maintains an eroding Pleistocene topography of two million years ago.. When the glaciers retreated for the last time around 7000 B.C., they changed the topography of the land, leaving poor and changed drainage systems behind, glacial lakes, the five Great Lakes, and Hudson Bay in Canada.
In this glacial age and intervals in Minnesota, many furry megafauna such as mammoths, musk oxen, giant beavers, mastadons and sloths lived in Minnesota's woods. For the region's flora (vegetation), the rich glacial till from Manitoba and other parts of Canada has produced an excellent growing medium. The Red River Valley has some of the nation's best topsoil.
The southern lobe of Glacial Lake Agassiz formed in the Northwestern portion of Minnesota from the glacial meltwater. The greater part of the lake was in Canada, and together took up an area larger than the current Great Lakes combined, being 110,000 square miles in area and 300 to 600 feet deep at that time. Glacial Lake Agassiz drained into the Glacial River Warren, now known as the Minnesota River Valley Lowland trench. The Minnesota River is only a fraction of its earlier size. Glacial Lake Duluth was the larger counterpart of Lake Superior. Near the bend in the Minnesota River at Mankato and going into Iowa in a north to south oblong of water, Glacial Lake Minnesota was a very large topographical entity. Other glacial lakes of Minnesota included Lake Grantsburg between the Twin Cities and Duluth and Lakes Upham and Aitkin existed in the Brainerd/Grand Rapids Area.
Southern Minnesota has been free of glacial ice since about 9,500 B.C. The last glacial lobe to quickly melt in this region was a Laurentide ice sheet of the Des Moines Lobe. Overall, Minnesota's lowest land areas were prehistorically the glacial water drainage basins. The northwestern border of Minnesota known as the Red River Valley of the north, the Minnesota River Valley, an enlarged Mississippi River Valley, Lake Superior, Saint Croix River Valley, and a low-lying area where Saint Paul-Minneapolis sit today, are all results of the glaciers. These are the glacial fingerprints. Today, these glaciers still exist in Greenland, and at Baffin Island in Northern Canada.
Anfinson, Scott F. "Southwestern Minnesota Archaeology: 12,000 Years In
The Prairie Lake
Region" Minnesota Historical Society Press; Saint Paul,
Minnesota, 1997.
Bray, Edmund C. "A Million Years In Minnesota: The Glacial Story of
the State" North Central Publishing Company; Saint Paul, Minnesota, 1962.
by: S.L. Burgstahler