Continental slope of central North America.
It stretches from the Rio Grande at the U.S.-Mexico border in the south to the Mackenzie River delta along the Arctic Ocean in the north and from the Interior Lowlands and the Canadian Shield in the east to the Rocky Mountains in the west. The plains embrace parts of 10 U.S. states and 4 Canadian provinces, covering an area of about 1,125,000 sq mi (2,900,000 sq km). A high plateau of semiarid grassland, these prairie regions in both the U.S. and Canada produce the major proportion of wheat grown in each country and are also important cattle-and sheep-herding areas. Parts of the plains have reserves of coal and lignite, petroleum, and natural gas.