The system extends for some 4,300 miles from Alaska southward to Central America, varying in width from 200 miles to about 1,100 miles. It consists of young fold-mountains, upfolded into three main ranges, which, in the extreme south, converge to form a single chain. The system may be divided into five well-defined sections.
(a) The Coast Ranges extend from Alaska to the Peninsula of California. In British Columbia they are submerged, except where their higher portions stand out as islands, such as Vancouver Island. Farther south the Coast Ranges separate the Central Valley of California from the Pacific.
(b) To the east of the Coast Ranges is a series of valleys. In British Columbia these valleys are 'drowned', being represented by the channel running between the mountain wall of the continent and the island-fringe.
(c) To the east of the- depressions rise lofty ranges known in north as the Alaskan Range, and farther south as the Cascade Mountains the Sierra Nevada.
(d) A series of intermont plateaux, lying between these ranges the main chain of the Rocky Mountains proper, includes the Yukon Plateau, the basaltic Snake River Plateau, the Great Basin of Land Drainage around the Great Salt Lake, and the Colorado and Mew Plateaux.
(e) Then come the Rocky Mountains proper. Their lofty peak dominates every landscape. Farther south majestic volcanoes, as Orizaba and Popocatepetl in the Eastern Sierra Madre, raise their snow-clad cones high above the Mexican Plateau. The Interior highlands have geologic history similar to that of the Appalachian plateau and the ridge and valley regions. The Arkansas River valley separates the northern Ozark Plateau from the Owachita Mountains to the south.
North American cordillera is a mixed landform. The Front Ranges of Colorado consist of intrusions of materials from deep within the earth that disturbed and uplifted the sedimentary layers. The Canadian Rockies are formed of folded and faulted sedimentary materials. These several ranges from Mexico to Alaska form a mountain system. The Pacific ranges extend from southern California along the Canadian coast and westward to the Alaskan peninsula. The inner part is formed by the Sierra Nevada of California, the cascades of Washington and Oregon, the coastal mountains of Canada and the Alaskan range. The coastal ranges in California have parallel mountains and valleys. Between these ranges lie some of the valleys like the Great Valley of California, the Willamette valley and the Puget Sound lowland. The coastal ranges are discontinuous in Canada and lowlands reappear in Alaska as the basins of the Alaskan and Aleutian ranges. Interior plateaus are of level upland. Normal elevation is around 910 meters. Yukon plain of Alaska and the Death Valley of California are the exceptions. The basin and range segment of Nevada, California and Utah is characterized by faulted mountain ranges partly buried in alluvium. The Colorado plateau has deeply cut Grand Canyon exposing several layers of sedimentary rocks (2743 - 3753 in).
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