United States: The Pacific Coast, Alaska, and Hawaii

The Pacific Coast, Alaska, and Hawaii

West of the Cascades and the Sierra Nevada and separated from them by a structural trough are the Coast Ranges, which extend along the length of the U.S. Pacific coast. The Central Valley in California, the Willamette Valley in Oregon, and the Puget Sound lowlands in Washington are part of the trough. The San Andreas Fault, a fracture in the earth's crust, parallels the trend of the Coast Ranges from San Francisco Bay SE to NW Mexico; earthquakes are common along its entire length. The Pacific Coastal Plain is narrow, and in many cases the mountains plunge directly into the sea. A coastline of emergence, it has few islands, except for California's Channel Islands and those in Puget Sound; there are few good harbors besides Puget Sound, San Francisco Bay, and San Diego Bay.

Alaska may be divided into four physiographic regions; they are, from north to south, the Arctic Lowlands, the coastal plain of the Arctic Ocean; the Rocky Mountain System, of which the Brooks Range is the northernmost section; the Central Basins and Highlands Region, which is dominated by the Yukon River basin; and the Pacific Mountain System, which parallels Alaska's southern coast and which rises to 20,310 ft (6,190 m) at Denali (Mt. McKinley), the highest peak of North America. The islands of SE Alaska and those of the Aleutian Islands chain are partially submerged portions of the Pacific Mountain System and are frequently subjected to volcanic activity and earthquakes. These islands, like those of Hawaii, are the tops of volcanoes that rise from the floor of the Pacific Ocean. Mauna Kea and Mauna Loa on Hawaii are active volcanoes; the other Hawaiian islands are extinct volcanoes.

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