Paleontology and geology

The alternating advance and retreat of glaciers dominated the Quaternary of Minnesota. The glaciers left behind thick blankets of poorly sorted, muddy sediment, as well as sand and gravel carried by streams formed from melting glacial ice. Enormous lakes, such as Lake Agassiz that covered over 300,000 square kilometers, formed south of the retreating ice sheets. Streams flowing out of these lakes carved the major river valleys that we see in Minnesota today. Mastodons, mammoths, musk ox, and other large mammals roamed the Quaternary landscape.