The
Laurentide Ice Sheet was a massive
sheet of ice that covered millions of square miles, including most of
Canada and a large portion of the northern
United States, multiple times during
Quaternary glacial epochs. It last covered most of northern North America between c. 95,000 and c. 20,000 years before the present day. At times, its southern margin included the modern sites of
New York City and
Chicago, and then followed quite precisely the present course of the
Missouri River up to the northern slopes of the
Cypress Hills, beyond which it merged with the
Cordilleran Ice Sheet. The ice coverage extended approximately as far south as 38 degrees latitude in the mid-continent.