Pacific Coast Ranges run from Alaska into Mexico
Officially the Pacific Mountain System in the United States, these ranges rim western North America from Alaska to northern and central Mexico. They form only the western belt of the broader Cordillera that also holds the Rockies, Sierra Nevada, and interior plateaus—yet naming fights still confuse Cascades with true coastal ridges.
The Western System includes Saint Elias, Coast, Insular, Olympic, Cascade, Oregon Coast, California Coast, Transverse, Peninsular, and Sierra Madre Occidental ranges. USGS Coast Range usage is narrower: south of Juan de Fuca to the California–Mexico line, west of Puget Sound, the Willamette, and the Central Valley. That stricter definition leaves out the Cascades, the Sierra Nevada and the Mojave and Sonoran deserts, while Canadians use the same label loosely for the Coast Mountains plus inland chains such as the Hazelton Mountains.
Character swings from Alaska’s record tidewater glaciers to chaparral, oak woodland and coastal sage scrub on the Transverse and Peninsular slopes. In British Columbia and Alaska the mountains break into a tangle of fjords and thousands of islands, and off Southern California the Channel Islands, an offshore extension of the Santa Monica Mountains, trail for about 260 kilometres.
River mouths punch coastal plains through the wall: the Copper in Alaska, the Fraser in British Columbia, the Columbia between Washington and Oregon, and in California the bay fed by the Sacramento and San Joaquin, the Oxnard Plain and Mission Bay. The Los Angeles Basin, squeezed between two range systems, holds sediment as much as 10 kilometres thick.
North of San Francisco Bay, cold unstable air from the Gulf of Alaska regularly slams into the western faces in winter, dropping heavy rain and snow. Farther south those storms come less often, and the peaks cast a rain shadow eastward that helps create the deserts beyond. Beneath it all, much of the margin is accreted terrane, from Alaska’s Wrangellia to Canada’s Chilliwack group: crustal fragments welded onto the continent over time.
Source: Pacific Coast Ranges
