With the completion of the study of Chicago's communities, Chicago History begins a new series exploring the resources of the Chicagoland area. These resources developed over thousands of years after the last Ice Age. It was these resources that enticed the Clovis people and later other Native Americans to the area and invited exploration by the French in the 1600s. As European Americans settled the land, they farmed and developed business and industry.
Continental glaciers assaulted Illinois and Chicago continually during the Ice Age between 2.4 million and 10,000 years ago. During the Ice age, the ice was 5,280 feet thick at Chicago. This weight of the glacier flattened, and depressed the land. On the edge of the glacier, mastodons and musk ox grazed near spruce forests. The average yearly temperature was close to freezing or below. Precipitation during the year was mostly snow. Rivers froze and were reduced to creeks. During warmer periods, water and sediment issued from the receding Laurentide Ice Sheet. This Wisconsinan Glaciation ended about 10,000 B.C.
The retreating glacier changed the land at the end of the Ice Age. Barren land appeared until plant life could take over. Lakes, rivers, swamps and marshes were widespread. Large glacial lakes were formed where moraines damned the water. Windblown dust (loess) was spread throughout the region by dust storms. Animals like bison, Jefferson’s ground sloth, mastodon, long-nosed peccary, saber-toothed cats, stag moose, woodland musk ox and woolly mammoth lived off the land. Spruce, balsam, poplar and aspen grew into forests. The region continued to change and develop in the years following the last Ice Age.
It took thousands of years for Chicagoland’s resources to develop after the Ice Age.
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