The central interior of the United States, a region bordered by the Rocky Mountains on the west and the Appalachians on the east, is a vast example of a lowland, or a low-lying, level expanse of countryside. During the Pleistocene ice age, huge glaciers moved into the region from Canada, covering most of the great wedge of land between the Missouri and Ohio Rivers, smoothing and flattening its contours. This glacially modified region is today called the Central Lowland.

Mary Swander