Plateau, or Tableland, an extensive area of flat or gently rolling land rising above the adjacent land, having one or many sharply elevated sides unless it is bounded by mountains. A plateau is often dissected, or cut, by rivers into different parts. Some dissected plateaus, such as the Colorado Plateau, retain their flat appearance even though crossed by deep canyons. Others, such as the Ozark Plateau, are so worn that they resemble hills or mountains rather than a plateau. In some places, a massif, or isolated mountain block, thrusts its peaks high above the surrounding surface of a plateau. Plateaus lie at widely varying elevations. For example, the Plateau of Tibet, surrounded by the Himalaya and Kunlun mountains, is as much as 15,000 feet (4,600 m) above sea level; the Allegheny Plateau of the Appalachian region, on the other hand, is not more than 3,000 feet (900 m) above sea level.