INTERIOR LOWLANDS

the broad, generally flat areas of the central part of the North American continent. The name is used in regional geologic and physiographic descriptions of North America and the conterminous United States. From the tectonic view, the continental Interior Lowlands are areas largely undisturbed by mountain building in past geologic time. They extend from central Saskatchewan, in Canada, south to the rim of the Coastal Plain and are bounded by the Great Plains on the west, the Canadian Shield on the north and east, and the Appalachian Mountains on the east. In the regional physiography of the conterminous United States, the Interior Lowlands are composed chiefly of the great Central Lowland of the Midwestern states and the Great Plains landform region to the west. Their related uplands include the Superior Upland, Appalachian Plateau (but not the Appalachian Mountains), the Interior Low Plateaus, and the Ozark Plateau.