The Great Lakes Map: These beautiful lakes owe their vast size to the latest ice age, when most of the earth's ice was concentrated in North America, and successive glacial advances and retreats repeatedly crossed the region.
Almost all of this water now flows to the Atlantic through the St Lawrence (Lake of the Woods and Minnesota's Red Lakes drain north through Lake Winnipeg to Hudson's Bay).
At higher stages Lake Erie drained through the Wabash, and Lake Michigan through the Illinois, south to the Gulf of Mexico. They probably will do so again after our present inter-glacial period ends.
Included on the map: The entire states of Wisconsin and Michigan, most of Minnesota, Iowa, and New York, and quite a bit of Ontario and Quebec.
Scale: 1:2 million 1"= about 32 miles