Great Plains

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Great Plains,

extensive grassland region on the continental slope of central North America. They extend from the Canadian provinces of Alberta, Saskatchewan, and Manitoba south through W central United States into W Texas. In the United States the Plains include parts of North Dakota, South Dakota, Montana, Wyoming, Colorado, Nebraska, Kansas, Oklahoma, New Mexico, and Texas.

Physical Geography

The Great Plains slope gently eastward from the foothills of the Rocky Mts. at an elevation of 6,000 ft (1,829 m) to merge into the interior lowlands at an elevation of roughly 1,500 ft (457 m). The 1,500 ft (457 m) contour line, the 100th meridian of longitude, and the 20-in. (51-cm) isohyet of precipitation are arbitrarily used to mark the region's transitional eastern border. In places, however, it is clearly marked by an escarpment. Much of the Great Plains was once covered by a vast inland sea, and sediments deposited by the sea make up the nearly horizontal rock strata that underlie the area. Intrusive igneous rocks account for sections of higher elevation. The Great Plains region has generally level or rolling terrain; its subdivisions include Edwards Plateau, the Llano Estacado, the High Plains, the Sand Hills, the Badlands, and the Northern Plains.

The Black Hills and several outliers of the Rocky Mts. interrupt the region's undulating profile. The Saskatchewan, Missouri, Platte, Republican, Arkansas, Cimarron, and Canadian rivers flow in wide beds, generally from west to east, and are important sources of water. Rainfall decreases from east to west. Except for its easternmost margin and the elevations, the Great Plains have a semiarid climate, averaging less than 20 in. (51 cm) of precipitation annually. There are wide seasonal temperature ranges and winds of high velocity. In the westernmost sections the chinook, a warm winter wind, brings relief from bitterly cold and snowy winters. The dominant type of vegetation consists of shortgrass prairies; trees grow in moister areas and along water courses.

People and Economy

Although overall the Great Plains are sparsely populated, with much of the grassland devoted to farms and ranches, about half the people live in small to medium-sized urban areas; Edmonton, Alberta and Denver, Colo. are the largest cities in the region. Soils throughout the region are fertile and very productive when water is available. The principal crop is wheat, concentrated in the Spring Wheat Belt (generally N of Nebraska), where the colder climate delays sowing until spring, and the Winter Wheat Belt (centered in Kansas and Oklahoma), where the milder climate allows for winter sowing. Other crops include sorghum, flax, and cotton. Cattle and sheep are raised throughout most of the Great Plains. Oil, natural gas, coal, and gold are among its mineral deposits.

History

The Great Plains were long inhabited by Native Americans, who hunted the teeming herds of buffalo (see bisonbison,
large hoofed mammal, genus Bison, of the cattle family. Bison have short horns and humped, heavily mantled shoulders that slope downward to the hindquarters.
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) that roamed the grasslands and, due to wholesale slaughter by settlers and the U.S. army, were nearly extinct by the end of the 19th cent. The region was explored by the Spanish in the 17th cent. Until well into the 19th cent., the central Great Plains were called the Great American Desert. The first westward-bound pioneers bypassed the Great Plains. The railroads were largely responsible for their development after the Civil War. An initial wave of settlement was followed by emigration in times of drought. By the mid-1930s, decades of overgrazing and poor soil management in many of the Plains states had resulted in dust storms and the devastation of crops (see Dust BowlDust Bowl,
the name given to areas of the U.S. prairie states that suffered ecological devastation in the 1930s and then to a lesser extent in the mid-1950s. The problem began during World War I, when the high price of wheat and the needs of Allied troops encouraged farmers to
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).

Bibliography

See W. P. Webb, The Great Plains (1931, repr. 1981); N. R. Peirce, The Great Plains States of America (1973); B. W. Blouet and F. C. Luebke, ed., The Great Plains: Environment and Culture (1979).

Great Plains

 

a foothill plateau bordering the Great Cordillera of North America, on the territory of the USA and Canada. The plains extend from the southeast to the northwest, from 29° to 62° N lat. They are 3,600 km long and 500-800 km wide. Geologically they are the edge of the North American (Canadian) platform. Under the plateau (at a depth greater than 1,000 m from the surface) there are Precambrian crystalline rocks, above which are Upper Paleozoic and Paleogenic and Neogenic sedimentary rocks (limestone, sandstone) and incoherent loesslike quaternary deposits, formed as a result of the accumulation of byproducts of the destruction of cordilleras. In certain parts these rocks have recent intrusions and are pressed into folds, which form solitary mountains and short ranges. The highest of these are the Black Hills (2,207 m).

The surface of the plateau gradually rises from 500 m in the east to 1,600-1,700 m in the west and is very eroded in a number of places by rivers, which form a thick net of valleys and benches up to 300 m high and 200-300 km long (the largest is Pine Ridge). The benches divide the Great Plains into distinct sections—the Edwards Plateau, the Llano Estacado, the High Plains, and the Missouri Plateau. South of 38° N. lat (the Edwards Plateau and the Llano Estacado), wide mesa heights with karstic forms predominate in sections formed from limestone. The central area is broken by a thick net of ravines up to 150 m deep; these form the so-called Badlands. North of 48° N. lat the Great Plains underwent Paleogenic glaciation and have a hilly morainic relief. The Great Plains are rich in oil, black and brown coal, natural gas, rare earth elements, and common salt.

The climate of the Great Plains is continental—temperate in the north and subtropical in the south. The average January temperature in the north is -28°C and 12°C in the south. The corresponding July temperatures are 13°C and 28°C. The yearly precipitation ranges east to west from 500 mm to 250 mm in the north and from 600 mm to 300 mm in the south. The Cordillera has a great influence on the climate, holding the moisture carried by winds from the Pacific. There is little snow in the winter, and warm dry west winds, called chinooks, occur frequently. Summers are dry, with occasional downpours and strong winds, which cause dust storms. Destructive whirlwinds, called tornadoes, are characteristic.

The rivers have little water and are swift, flowing in deep valleys. The height of the runoff is 1-3 cm. In the summer after downpours the rivers often jump their banks. In the winter the upper reaches dry up (occasionally at a length of 200-300 km from the source). In the north the rivers are covered by ice for five or six months but do not freeze over in the south. The largest rivers, the Missouri, Platte, Arkansas, Colorado, and Pecos, are widely used for irrigation.

The soil is mostly chestnut. North of 51° N. lat chernozem, gray forest, and soddy podzolic soils predominate. On the southern edge it is cinnamon-colored and gray brown. In many regions the soil has suffered badly from erosion. The greater part of the Great Plains is covered by dry grama steppe (grama grass, buffalo grass, wire grass, and ephemeroids, such as mountain lily, easter lily, phlox, and succulents), which alternates in places that are not as dry with grama- and arrow-grass steppe. In the Canadian parts of the Great Plains forest steppe predominates—that is, a combination of sparse aspen and poplar forests and areas of meadow steppe with various types of grasses; in the north the steppe turns into southern taiga (white spruce, larch, poplar, birch, and aspen). On the Llano Estacado and Edwards Plateau there is found subtropical savanna, in which mesquite, acacia, grasslike vegetation of the dry steppes, and succulents (yucca, various types of cactus, and others) predominate.

The animal population of the Great Plains has been seriously depleted by man. Bison, which formerly inhabited the plains in abundance, are kept in reserves (the most important are the Wood Buffalo and Elk Island in Canada). The Plains wolf (coyote), prairie dog, and rodents (ground squirrel, marmot, and others) are found. There are many steppe birds, such as prairie chickens, turkey vultures, and others. In the south there are reptiles, among which is the rattlesnake. The basic types of agricultural utilization of the Great Plains are cattle grazing and, on irrigated land, farming (where cotton, potatoes, sugar beets, and fodder grasses are raised). In the north the land is used mainly for dry farming (mostly wheat) and forestry.

REFERENCES

A. Boli, Severnaia Amerika Moscow, 1948. (Translated from French.)
Ignat’iev, G. M. Severnaia Amerika, Moscow, 1965.
Kanada: Geograficheskie raiony. Moscow, 1955. (Translated from English.)

G. M. IGNAT’IEV

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