plateau, elevated, level or nearly level portion of the earth's surface, larger in summit area than a mountain and bounded on at least one side by steep slopes, occurring on land or in oceans. Some plateaus, such as the Deccan of India and the Columbia Plateau of the NW United States, are basaltic and were formed as the result of a succession of lava flows covering hundreds of thousands of square miles that built up the land surface. Others are the result of upward folding; still others have been left elevated by the erosion of adjacent lands. Plateaus, like all elevated regions, are subject to dissection by erosion, which removes greater amounts of the upland surface. Low plateaus are often agricultural regions, while high plateaus are usually fit chiefly for stock grazing. Many of the world's high plateaus are deserts. Other notable plateaus are the Colorado Plateau of the W United States, the Bolivian plateau in South America, and the plateaus of Anatolia, Arabia, Iran, and the Tibet region of China.

Mogollon Plateau or Mogollon Mesa, tableland, part of the Colorado Plateau, from 7,000 to 8,000 ft (2,134-2,438 m) high, E central Ariz. It is covered by pine forests, parts of which are included in Coconino, Tonto, and Sitgreaves national forests. Its southern edge is a rugged escarpment called the Mogollon Rim. The plateau is not directly connected with the Mogollon Mts. in W New Mexico.

Laurentian Plateau, Canada: see Canadian Shield.

Jos Plateau, region, c.3,000 sq mi (7,770 sq km), alt. c.4,200 ft (1,280 m), central Nigeria, W Africa. The plateau, composed mainly of granite, slopes gently to the north and is covered by grasslands; the Gongola River rises there. The region has one of the higher population densities in Nigeria and is freer from disease than the surrounding lowlands. Tin is mined and processed on the plateau, and farming and grazing are important. The town of Jos is the region's chief center. In the 19th cent. the plateau was a refuge for non-Islamic people fleeing from the Islamic Fulani people.

Cumberland Plateau or Cumberland Mountains, southwestern division of the Appalachian Mt. system, extending northeast to southwest through parts of West Virginia, Virginia, Kentucky, and Tennessee into N Alabama. Black Mt., Ky., is the highest point (4,145 ft/1,263 m). On the east the plateau rises sharply from the Great Valley of E Tennessee; on the west the slope is rough and broken. The plateau is the source of the Cumberland River and several tributaries of the Tennessee. The surrounding region, which is sparsely populated, yields various minerals, such as coal, limestone, and sandstones. The region is also laden with trees, and the forests make for an important resource. There are some agricultural subsistence settlements in the area. Cumberland Gap provides a natural passage through the Cumberland Mts., a ridge of the plateau.

Columbia Plateau, physiographic region of North America, c.100,000 sq mi (259,000 sq km), NW United States, between the Rocky Mts. and the Cascade Range in Washington, Oregon, and Idaho. Most of the plateau is underlaid by deposits, more than 10,000 ft (3,048 m) thick in places, of lava (mainly basalt) interbedded with sedimentary rock; older rocks outcrop in the Blue and Wallowa mts. Young lavas, scattered cinder cones, volcanic ash, and barren landscapes (including Craters of the Moon National Monument) are features of the Snake River plain in the south. Older, decayed lavas, much modified by accumulations of loess, occur in the north in the Columbia basin section; coulees (dry river canyons) and scablands (extensively eroded basalt surfaces), both carved by glacial meltwaters, are features of the region. The Columbia Plateau is an important agricultural and grazing area and is a major source of hydroelectric power.

Colorado Plateau, physiographic region of SW North America, c.150,000 sq mi (388,500 sq km), in Arizona, Utah, Colorado, and New Mexico, including the "Four Corners" area. It is characterized by broad plateaus, ancient volcanic mountains at elevations of c.5,000 to 13,000 ft (1,520-3,960 m), and deeply dissected canyons lined with often brightly colored sedimentary and volcanic rocks, including the Grand Canyon of the Colorado River. Native American reservations occupy about one third of the mostly semiarid and sparsely vegetated area, which was the last U.S. region to be explored by whites. About one half of the public land is used for grazing. Among many ancient cliff dwellings are those at Mesa Verde and Canyon de Chelly. The region has a number of U.S. national parks and monuments.

Chotts, Plateau of the [Arab.,=salt lake], plateau region of the Atlas Mts., alt. c.3,500 ft (1,070 m), N Algeria, N Africa. The plateau is c.125 mi (200 km) wide in the west, narrowing in the east to become a series of valleys. Enclosed by the Tell Atlas in the north and the Saharan Atlas in the south, the region has interior drainage, a semiarid climate, and is dotted with salt lakes and salt flats. Its grasslands support nomadic herding. The name is also spelled Shotts.

Bié Plateau or Bihé Plateau, highland region, western section of the central plateau of Angola, SW Africa; alt. 5,000 to 6,000 ft (1,520-1,830 m). Its cool climate and ample rainfall make it possible for corn, sisal, peanuts, sugarcane, rice, and coffee to be raised there. It is linked to the sea by the Benguela Railway. Huambo and Cuito are the chief towns.

Allegheny Plateau, dissected plateau, western part of the Appalachian Mts., extending c.500 mi (800 km) SW from N Pa. to SW Va., rising to c.4,860 ft (1,480 m) at Spruce Knob, the highest peak in West Virginia. The E Allegheny Plateau, known as the Allegheny Mountains or the Alleghenies, has a steep eastward-facing escarpment often called the Allegheny Front (c.1,500-1,600 ft/460-490 m high) and is more rugged than the western portion. The plateau, formed by the folding of sedimentary rocks, has been subsequently reduced by erosion. The mountains, rich in coal and timber, also contain iron ore, petroleum, and natural gas.

or submarine plateau

Large submarine elevation rising sharply at least 660 ft (200 m) above the surrounding seafloor and having an extensive, relatively flat or gently tilted summit. Most plateaus are steplike interruptions of the continental slopes. Some, however, occur well beyond the continental margins. They stand alone, high above the surrounding seafloor, and are believed to be fragments of continents that were isolated during continental drift and seafloor spreading.

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Extensive area of flat upland, usually bounded by an escarpment on all sides but sometimes enclosed by mountains. Plateaus are extensive, and together with enclosed basins they cover about 45percnt of the Earth's land surface. The essential criteria for a plateau are low relative relief and some altitude. Low relief distinguishes plateaus from mountains, although their origin may be similar. Plateaus, being high, often create their own local climate; the topography of plateaus and their surroundings often produce arid and semiarid conditions.

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Tableland in the U.S. that forms the western section of the Appalachian Mountains and a part of the Allegheny Plateau. It extends southwest for 450 mi (725 km) from southern West Virginia to northeastern Alabama, averages 50 mi (80 km) in width, and is 2,000–4,145 ft (600–1,263 m) high. The roughest and highest portion is a narrow ridge about 140 mi (225 km) long that forms its eastern margin in eastern Kentucky and northeastern Tennessee; the name Cumberland Mountains is generally applied to this area, which includes the Cumberland Gap National Historical Park. The plateau has large deposits of coal, limestone, and sandstone.

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