| Summary: | temperatures were about eight to 10�F cooler than interglacial times. Although during earlier times glaciers had moved even farther south, ice sheets extended as far south as the present Missouri River valley during the last of the major glacial incursions. This was called the Wisconsinan glaciation, and it occurred about 20,000 years ago. Because of the huge amount of water frozen as glacial ice, during this glacial maximum the center of the North American ice sheet in Canada was about two miles thick and the global sea level was about 400 feet lower than today. These glaciers altered river courses and molded the landscape, creating the gently rolling, hilly topography seen in most areas of North Dakota today. Tundra and northern spruce forest habitats, like those in northern Canada today, developed in front of the glaciers. When the glaciers melted sediment that had been incorporated in the ice was deposited on the land surface, which is called glacial till. This painting depicts the Ice Age woolly mammoth, Mammuthus. (Figure 22) 32 201 1-2013 North Dakota Blue Book
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