GREAT PLAINS

also called Great American Desert, major North American physiographic province, stretching 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 the three Prairie Provinces and portions of the Northwest Territories of Canada. Varying in east-west width from 300 to 700 miles (500 to 1,100 km), the Great Plains cover an area of about 1,125,000 square miles (2,900,000 square km), roughly equivalent to one-third the area of the United States. The Rocky Mountains define the western boundary for their entire 3,000-mile (4,800-kilometre) north-south length. The Great Plains slope gently to the east, where they merge with the Interior Lowlands. In the United States this eastern boundary is marked at some points by a low escarpment that runs intermittently from Texas to North Dakota, generally somewhat eastward of the 100th meridian. In the Canadian portion the line dividing the Great Plains from the Canadian Shield cuts through Lake Winnipeg in the south before curving northwestward through Lake Athabasca, Great Slave Lake, and Great Bear Lake. The Great Plains are a vast high plateau of semiarid grassland. Their elevation at the base of the Rockies in the United States is between 5,000 and 6,000 feet (1,500 and 1,800 m) above sea level; this decreases gradually to 1,500 feet (460 m) at their eastern boundary. The elevations of the Canadian portion are lower, and near the Arctic Ocean the surface is only slightly above sea level. Much of the plains area consists of gently tilted shale, limestone, and sandstone discontinuously mantled by glacial deposits (in the north) and by loess and alluvial deposits. Although the plains are generally pictured as flat to rolling, conspicuous land forms characterize some of their parts; among these are the Black Hills of South Dakota and Wyoming and the Badlands of South Dakota. Over much of the Great Plains' expanse, cold winters and warm summers prevail, with low precipitation and humidity, much wind, and sudden changes of temperature. The prairie regions in both the United States and Canada produce the major proportion of the wheat grown in each country and are also important cattle- and sheep-herding areas. Until recently the cultivation of the Great Plains' vast stretches of arable land was at the mercy of rainfall that is scanty (often less than 15 inches annually) and undependable. Irrigation in the United States, tapping the region's widespread aquifers, has temporarily freed agriculture from the vagaries of a dry climate. Parts of the plains have considerable reserves of coal and lignite, petroleum, and natural gas. The Mississippi River basin and its drainage network. also called Great American Desert, major physiographic province of North America. The Great Plains lie between the Rio Grande in the south and the delta of the Mackenzie River at the Arctic Ocean in the north and between the Interior Lowland and the Canadian Shield on the east and the Rocky Mountains on the west. Their length is some 3,000 miles (4,800 kilometres), their width from 300 to 700 miles, and their area approximately 1,125,000 square miles (2,900,000 square kilometres), roughly equivalent to one-third of the United States. Parts of 10 states of the United States (Montana, North Dakota, South Dakota, Wyoming, Nebraska, Kansas, Colorado, Oklahoma, Texas, and New Mexico) and the three Prairie Provinces of Canada (Manitoba, Saskatchewan, and Alberta) and portions of the Northwest Territories are within the Great Plains proper. Some writers have used the 100th west meridian as the eastern boundary, but a more precise one is an eastward-facing escarpment that runs from Texas to North Dakota, generally somewhat east of the 100th meridian. In the Canadian portion the line dividing the Great Plains from the Canadian Shield runs east of the Red River of the North, cuts through Lake Winnipeg, and then curves northwestward, crossing Lake Athabasca, Great Slave Lake, and Great Bear Lake; in the far north, the plains reach the Arctic Ocean in a narrow strip just west of the Mackenzie delta. Additional reading The physical environment of the Great Plains is described in Tim Fitzharris, The Wild Prairie: A Natural History of the Western Plains (1983); and Claude A. Barr, Jewels of the Plains: Wild Flowers of the Great Plains Grasslands and Hills (1983). Ian Frazier, Great Plains (1989), combines a discussion of the landscape with a survey of social life and customs. The first important historical account of the Great Plains was Walter Prescott Webb, The Great Plains (1931, reprinted 1981). Webb's brilliant interpretation of cultural adaptation is extended in Carl Frederick Kraenzel, The Great Plains in Transition (1955). The past and present of North American Indian culture are explored in Robert H. Lowie, Indians of the Plains (1954, reprinted 1982); Preston Holder, The Hoe and the Horse on the Plains: A Study of Cultural Development Among North American Indians (1970, reprinted 1991); and Peter Iverson (ed.), The Plains Indians of the Twentieth Century (1985). Mari Sandoz, Old Jules (1935, reprinted 1985), is a classic novel on the frontier and pioneer life of European settlers. John W. Bennett, Northern Plainsmen: Adaptive Strategy and Agrarian Life (1969, reissued 1976), is an anthropologist's analysis of modern trends for the Canadian plains. John L. Dietz