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The Natural Environment

Natural Regions

North America can be divided into five major natural regions. The eastern half of Canada, as well as most of Greenland and sections of Minnesota, Wisconsin, Michigan, and New York in the United States, are part of the Canadian Shield (or Laurentian Plateau), which is a plateau region underlain by ancient crystalline rocks. The region has poor soil, and dense forests cover much of its southern part. A second region is made up of a coastal plain in most of the eastern United States and Mexico. In the United States the coastal plain is bordered on the west by a third region, comprising a relatively narrow cordillera of mountains and hills, notably the rounded Appalachian Mountains. A fourth region consists of the central portion of the continent, from southern Canada to southwestern Texas, which encompasses an extensive lowland that has experienced alternating periods of submergence beneath the sea and uplift, with the result that it is deeply covered with layers of sedimentary rock. It is not an uninterrupted flatland but includes much undulating and even hilly terrain, such as the Ozark Plateau. The western portion is made up of the Great Plains, which slope upward to the foot of the Rocky Mountains.

The fifth, and westernmost, region of North America, taking in most of Mexico, is an active zone of mountain building; its recent geological history is dominated by crustal movements and volcanic activity. Adjacent to the Great Plains in the United States and Canada are the Rocky Mountains, which are geologically related to the Sierra Madre Oriental range of Mexico. To the west is an area of scattered basins and high plateaus, including the Interior Plateau of British Columbia in Canada, the Colorado Plateau and the Great Basin of the United States, and the vast central plateau of Mexico. Along the Pacific coast are a number of lofty mountain systems, extending from the Alaska Range to the Sierra Madre Occidental and Sierra Madre del Sur of Mexico. In between are ranges such as the Coast Mountains of British Columbia and the Cascade Range, the Coast Ranges, and the Sierra Nevada of the United States. Interspersed are some low-lying areas, notably the fertile Central Valley of California. The highest point in North America, Mount McKinley, or Denali (6,194 m/20,320 ft), is situated in the Alaska Range, and the lowest point, 86 m (282 ft) below sea level, is in Death Valley, California, a part of the Great Basin.

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