Not long ago as geology goes — nine, ten, twelve millennia — one of the world’s largest lakes covered most of Minnesota, plus much of North Dakota, Manitoba, Saskatchewan, Ontario and a corner of South Dakota. It’s called Lake Agassiz, named after the scientist Louis Agassiz, who figured out the Ice Age (continental glaciation, basically), and whose statue dropped head-first into the concrete in the 1906 earthquake.
Evidence of the late lake s not obvious unless you look in winter, from altitude. I did that while flying west the week before last. Here’s the photo set I shot. Those lines you see in the farmland are old shorelines of the lake. Since it was a glacial lake — a large puddle left by the effect of global warming on the ice cap — these lines I suppose also qualify as glacial moraine. Anyway, interesting shit. To me, at least.
By the way, the straight lines in the shot above are wind breaks made of trees or hedges. (Not sure.). The larger square or rectangular dark areas are woodlots. The setting is a spot almost exactly where South Dakota, North Dakota and Minnesota meet. I believe it is in South Dakota.
By the way, what remains of Lake Agassiz is Lake Winnepeg, Minnesota’s ten thousand lakes (See this comment below for the correction, and a larger number scattered around three provinces of Canada.