If such iconic landscapes as the Great Lakes, the Mississippi Basin and New York Harbor are proof of anything, it's that the North America we know has been shaped by ice ages coming and going and coming back again in the last two-and-a-half million years of Earth's history.

What sorts of geographical differences within Western North America (from Nebraska to the Pacific coast) would I expect to see if the ice ages have been lasting for 14 million years instead of two-and-a-half?