USA – May 5th, 2013
The Pacific Coast Ranges (in Canada) and the Pacific Mountain System (in the United States) are the series of mountain ranges that stretch along the West Coast of North America from Alaska south to Northern and Central Mexico. Both the Canadian and United States portions are often referred to as Pacific Coast Ranges.
The Pacific Coast Ranges are part of the North American Cordillera, which includes the Rocky Mountains, Columbia Mountains, Interior Mountains, the Interior Plateau, Sierra Nevada Mountains, the Great Basin mountain ranges, and other ranges and various plateaus and basins. The Pacific Coast Ranges designation, however, only applies to the Western System of the Western Cordillera, which comprises the Saint Elias Mountains, Coast Mountains, Insular Mountains, Olympic Mountains, Cascade Range, Oregon Coast Range, California Coast Ranges, Transverse Ranges, Peninsular Ranges, and the Sierra Madre Occidental.
The character of the ranges varies considerably, from the record-setting tidewater glaciers in the ranges of Alaska, to the rugged Central and Southern California ranges, the Transverse Ranges and Peninsular Ranges, in the chaparral and woodlands ecoregion with Oak Woodland, Chaparral shrub forest or Coastal sage scrub-covering them.
The coastline often drops steeply into the sea. Along the British Columbia and Alaska coast, the mountains intermix with the sea in a complex maze of fjords, with thousands of islands. There are coastal plains at the mouths of rivers that have punched through the mountains spreading sediments, most notably at the Copper River in Alaska, the Fraser River in British Columbia, and the Columbia River between Washington and Oregon. In California, sediments are spread by the Sacramento and San Joaquin Rivers into the San Francisco Bay, by the Santa Clara River to Oxnard Plain (home to some of the most fertile soil in the world), and by the Los Angeles, San Gabriel, and Santa Ana Rivers to the Los Angeles Basin – a coastal sediment-filled plain between the peninsular and transverse ranges with sediment in the basin up to 6 miles (10 km) deep.
From the vicinity of San Francisco Bay north, it is common in winter for cool unstable air masses from the Gulf of Alaska to make landfall in one of the Coast Ranges, resulting in heavy precipitation, both as rain and snow, especially on their western slopes. The same Winter weather occurs with less frequency and precipitation in Southern California, with the mountains’ western faces and peaks causing an eastward rainshadow that produces the arid desert regions.