| Pacific Coast Ranges | |
|---|---|
 Canadian Coast Range, Whistler, British Columbia | |
| Highest point | |
| Peak | Mount Logan |
| Elevation | 5,959 m (19,551 ft) |
| Dimensions | |
| Length | 3,800 mi (6,100 km) |
| Geography | |
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| Countries |
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| Parent range | North American Cordillera |
ThePacific Coast Ranges (officially gazetted as thePacific Mountain System[1] in theUnited States;French:chaînes côtières du Pacifique;Spanish:cadena costera del Pacífico)[2] are the series ofmountain ranges that stretch along the West Coast ofNorth America fromAlaska south to northern and centralMexico. Although they are commonly thought to be the westernmost mountain range of the continental United States and Canada, the geologically distinctInsular Mountains ofVancouver Island lie farther west.
The Pacific Coast Ranges are part of theNorth American Cordillera (sometimes known as the Western Cordillera, or inCanada, as the Pacific Cordillera and/or the Canadian Cordillera), which includes theRocky Mountains, theColumbia Mountains, theInterior Mountains, theInterior Plateau, theSierra Nevada, theGreat Basin mountain ranges, and other ranges and various plateaus and basins.
ThePacific Coast Ranges designation, however, only applies to the Western System of the Western Cordillera,[3] which comprises theSaint Elias Mountains,Coast Mountains,Insular Mountains,Olympic Mountains,Cascade Range,Oregon Coast Range,California Coast Ranges,Transverse Ranges,Peninsular Ranges, and theSierra Madre Occidental.
The termCoast Range is used by theUnited States Geological Survey to refer only to the ranges south of theStrait of Juan de Fuca inWashington to theCalifornia-Mexico border, and to those west ofPuget Sound, theWillamette Valley, and theSacramento andSan Joaquin valleys (theCalifornia Central Valley).That definition excludes theSierra Nevada andCascade Ranges, theMojave(High), andSonoran(Low) Deserts,[4] i.e. thePacific Border province. The same term is used informally in Canada to refer to theCoast Mountains and adjoining inland ranges such as theHazelton Mountains, and sometimes also theSaint Elias Mountains.
The character of the ranges varies considerably, from the record-settingtidewater glaciers in the ranges of Alaska, to the rugged Central andSouthern California ranges, theTransverse Ranges andPeninsular Ranges, in thechaparral and woodlands eco-region withOak Woodland,Chaparral shrub forest orCoastal sage scrub-covering them. The coastline is often seen dropping steeply into the sea with photogenic views. Along theBritish Columbia and Alaska coast, the mountains intermix with the sea in a complex maze offjords, with thousands of islands. Off the Southern California coast theChannel Islandsarchipelago of theSanta Monica Mountains extends for 160 miles (260 km).
There arecoastal plains at the mouths of rivers that have punched through the mountains spreading sediments, most notably at theCopper River in Alaska, theFraser River in British Columbia, and theColumbia River between Washington and Oregon. In California: theSacramento andSan Joaquin Rivers'San Francisco Bay, theSanta Clara River'sOxnard Plain, the Los Angeles, San Gabriel, and Santa Ana Rivers'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, and the San Diego River'sMission Bay.
From the vicinity of San Francisco Bay north, it is common in winter for cool unstable air masses from theGulf of Alaska to make landfall in one of the Coast Ranges, resulting in heavyprecipitation, both asrain andsnow, 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 eastwardrainshadow that produces the ariddesert regions.
Omitted from the list below, but often included is the Sierra Nevada, a major mountain range of eastern California that is separated by the Central Valley over much of its length from the California Coast Ranges and the Transverse Ranges.[5]
On the West coast of North America, the coast ranges and the coastal plain form the margin. Most of the land is made ofterranes that have beenaccreted onto the margin. In the north, the insular belt is an accreted terrane, forming the margin. This belt extends from theWrangellia Terrane in Alaska to the Chilliwack group of Canada.[6]
A rupture inRodinia 750 million years ago formed a passive margin in the eastern Pacific Northwest. The breakup ofPangea 200 million years ago began the westward movement of the North American plate, creating an active margin on the western continent. As the continent drifted West, terranes were accreted onto the west coast.[6] The timing of the accretion of the insular belt is uncertain, although the closure did not occur until at least 115 million years ago.[6] OtherMesozoic terranes that accreted onto the continent include theKlamath Mountains, the Sierra Nevada, and the Guerrero super-terrane of western Mexico.[7] 90–80 million years ago the subductingFarallon plate split and formed theKula Plate to the North. This formed an area in what is now Northern California, where the plates converged forming aMélange. North of this was theColumbia Embayment, where the continental margin was east of the surrounding areas.[6] Many of the majorbatholiths date from the lateCretaceous.[7] As theLaramide Orogeny ended around 48 million years ago, the accretion of theSiletzia terrane began in the Pacific Northwest. This began the volcanic activity in theCascadia subduction zone, forming the modern Cascade Range, and lasted into theMiocene. Events here may relate to theignimbrite flare-up of the southernBasin and Range.[8] As extension in the Basin and Range Province slowed by a change inNorth American Plate movement circa 7 to 8 Million years ago, rifting began on theGulf of California.[8]
Although many of the ranges do share a common geologic history, the Pacific Coast Ranges province is not defined by geology, but rather by geography. Many of the various ranges are composed of distinct forms of rock from many different periods of geological time from thePrecambrian in parts of theLittle San Bernardino Mountains to 10,000-year-old rock in the Cascade Range. For one example, the Peninsular Ranges, composed of Mesozoic batholitic rock, are geologically extremely different from theSan Bernardino Mountains, composed of a mix of Precambrian metamorphic rock and Cenozoic sedimentary rock. However, both are considered part of the Pacific Coast Ranges due to their proximity and similar economic and social impact on surrounding communities.
These are the members of the Pacific Coast Ranges, from north to south:
These are not named as ranges, but amount to the same thing. The Pacific Coast Ranges are home to the largest temperate-latitude icefields in the world.
Only the largest icefields are listed above; smaller icefields may be listed on the various range pages. Formally unnamed icefields are not listed
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