| North American Cordillera | |
|---|---|
.JPG) A mountain inDenali National Park | |
| Highest point | |
| Peak | Denali |
| Elevation | 6,190 m (20,310 ft) |
| Dimensions | |
| Length | 6,400 km (4,000 mi) |
| Geography | |
 The mountainous western part of North America is called a "cordillera". | |
| Countries |
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TheNorth American Cordillera, sometimes also called theWestern Cordillera of North America, theWestern Cordillera, or thePacific Cordillera,[1][2] is theNorth American portion of theAmerican Cordillera, the mountain chain system along thePacific coast of theAmericas. The North American Cordillera covers an extensive area ofmountain ranges,intermontanebasins, andplateaus inWestern andNorthwestern Canada,Western United States, andMexico, including much of the territory west of theGreat Plains.
The precise boundaries of this cordillera and its subregions, as well as the names of its various features, may differ depending on the definitions in each country or jurisdiction, and also depending on the scientific field; this cordillera is a particularly prominent subject in the scientific field ofphysical geography.[3][4]
The North American Cordillera extends from theU.S. state ofAlaska to the southern border ofMexico, and includes some of the highest peaks on the continent.[5] Its mountain ranges generally run north-to-south along three main belts: thePacific Coast Ranges in the west, the Nevadan belt in the middle (including theSierra Nevada), and the Laramide belt in the east (including theRocky Mountains).[6][7][8]
These threeorogenic belts (also called "orogens") arose due to the engagement oftectonic plates which deformed the Earth'slithosphere (crust and uppermost mantle). For example, theLaramide orogeny changed thetopography of the central Rocky Mountains and adjoining Laramide regions (from central Montana to central New Mexico) during theLate Cretaceous 80 million years ago.[9] Prior to this time the Rocky Mountain region was occupied by a broad basin. Further topographical evolution occurred during theEocene (55–50 million years ago) andOligocene (34–23 million years ago), but since that time, the region has been relatively stable.[10][11][12][13] Generally speaking, it will be convenient here to consider these three belts going west to east, and north to south.
InAlaska, south of the Interior Plains area, is the Rocky Mountain System, then the Intermontane Basins and Ranges, and in the southern part of the state are the Pacific Mountains and Valleys.[14] In theAlaska panhandle, the mainland mountain ranges and offshore islands (theAlexander Archipelago) are extensions of respective ranges further south.[15]
In Canada, the North American Cordillera is usually divided into three physiographic regions: the western system, the interior system, and the eastern system.[16] The western system includes theCoast Mountains, the interior system includes theColumbia Mountains, and the eastern system includes theCanadian Rockies.[3]
At its midsection betweenSan Francisco,California, andDenver,Colorado, the North American Cordillera is about 1,000 miles (1,600 km) wide, and its physiographic provinces at this midpoint are as follows, going from west to east: the Pacific Coast Ranges, theCentral Valley, the Sierra Nevada, theBasin and Range Province (forming many narrow ranges and valleys), theColorado Plateau, and the Rocky Mountains.[5] In the United States, another major feature of the Cordillera is theColumbia Plateau, located north of California between theCascade Range – which is a northern extension of the Sierra Nevada[17] – and the Rocky Mountains.
In Mexico, theSierra Madre Occidental, and theSierra Madre Oriental further east, surround theMexican Plateau.[17][18] To the west of the Sierra Madre Occidental, thePeninsular Ranges border the Pacific Ocean, and theSierra Madre del Sur is the southern extension of the Peninsular Ranges.[19] Sierra Madre means "Mother Range" in Spanish.
The Nevadan belt runs up and down the middle of the North American Cordillera. Therefore, the intermontane areas of the cordillera can be divided up into the areas east of the Nevadan belt, and those west of the Nevadan belt.
The Pacific Coast Ranges, comprising the Pacific Coast Belt, parallel the North American Pacific Coast, and comprise several mountain systems. Along theBritish Columbia and Alaska coasts, 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).
In southern Alaska, the primary mountain ranges are theAlaska Range,Wrangell Mountains,Saint Elias Mountains,Kenai Mountains,Chugach Mountains, andTalkeetna Mountains.[20][21]
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TheYukon Ranges comprise themountains in the southeastern part of theU.S. state ofAlaska and most of theYukon, Canada. This range has an area of 364,710 km2 (140,820 sq mi).[22]
TheCoast Mountains run from the lowerFraser River and theFraser Canyon northwestward, separating theInterior Plateau from the Pacific Ocean.[23] Their coastal flank is characterized by an intense network of fjords and associated islands, very similar to theNorwegian coastline, while their inland side against the plateau transitions to the high plateau in dryland valleys notable for a series of large lakes similar to the alpine lakes of southern Switzerland, beginning in deep mountains and ending in flatland. They are subdivided in three main groupings, thePacific Ranges between the Fraser andBella Coola, theKitimat Ranges from there northwards to theNass River, and theBoundary Ranges from there to their terminus in theYukon Territory atChampagne Pass andChilkat Pass northwest ofHaines, Alaska.[23] TheSaint Elias Mountains lie to their west and northwest, while theYukon Ranges and Yukon Basin lie to their north. On the inland side of the Boundary Ranges are theTahltan andTagish Highlands and also theSkeena Mountains, part of theInterior Mountains system, which also extend southwards on the inland side of theKitimat Ranges.[23]
The terrain of the main spine of the Coast Mountains is typified by heavy glaciation, including several very large icefields of varying elevation. Of the three subdivisions, the Pacific Ranges are the highest and are crowned byMount Waddington, while the Boundary Ranges contain the largest icefields, theJuneau Icefield being the largest. The Kitimat Ranges are lower and less glacier-covered than either of the other two groupings, but are extremely rugged and dense.
The Coast Mountains are made ofigneous andmetamorphic rock from an episode ofarc volcanism related tosubduction of theKula andFarallon Plates during theLaramide orogeny about 100 million years ago.[24] The widespreadgranite forming the Coast Mountains formed when magma intruded and cooled at depth beneath volcanoes of theCoast Range Arc, whereas the metamorphic formed when intruding magma heated the surrounding rock to produceschist.
TheInsular Mountains extend fromVancouver Island in the south toHaida Gwaii in the north on theBritish Columbia Coast. It contains two main mountain ranges, theVancouver Island Ranges on Vancouver Island and theQueen Charlotte Mountains on Haida Gwaii.[25]
TheOlympic Mountains is amountain range on theOlympic Peninsula of westernWashington in theUnited States. Themountains, part of thePacific Coast Ranges, are not especially high –Mount Olympus is the highest at 7,962 ft (2,427 m) – but the western slopes of the Olympics rise directly out of thePacific Ocean and are the wettest place in the contiguous 48 states.[26][27] Most of the mountains are protected within the bounds of theOlympic National Park.
South of the Olympics lies theChehalis River valley representing a break in elevation and drainages, followed by theWillapa Hills. The highest peak in the Willapa Hills isBoistfort Peak with an elevation of 3,113 feet (949 m).[28] This region represents the lowest of the upland ares in the Pacific Coast Ranges.
TheOregon Coast Range is the part of the Coast Range system that is denoted as between the mouth of theColumbia River and theMiddle Fork Coquille River. It is about 200 miles (320 km) long. The highest peak isMarys Peak, at 4,101 ft (1,250 m).
TheCalifornia Coast Ranges are one of the eleven traditional geomorphic provinces of California. This province includes several – but not all – mountain ranges along the California coast (theTransverse Ranges,Peninsular Ranges, andKlamath Mountains are not included).[29]
TheSierra Madre del Sur mountains in southwestern Mexico form a southern extension of thePeninsular Ranges ofBaja California.[19] The Peninsular Ranges are separated from the Sierra Madre del Sur by an expanse of ocean.
The Nevadan belt is located between the Pacific coast belt and the Laramide belt.Nevada means "snow-covered" in Spanish.
In Canada, theNorthern Interior Mountains are a northern extension of the Columbia Mountains.[30] They include theHazelton Mountains,Cassiar Mountains,Omineca Mountains, andSkeena Mountains.
TheColumbia Mountains are a designation in British Columbia for a group of four ranges lying between theRocky Mountain Trench (to the east) and theInterior Plateau (to the west). These ranges are theCariboo Mountains, which are the northernmost and sometimes considered to be part of the Interior Plateau, theSelkirk Mountains, thePurcell Mountains, and theMonashee Mountains.
The Columbia Mountains are classified as being in Canada's interior system, rather than its eastern system.[31] However, the Columbia Mountains are an extension of mountains in the United States that are considered part of the Rocky Mountains, and therefore the Columbia Mountains are often treated as being part of the Rockies.[32]
The Selkirks and Purcells lie entirely within the basin of the Columbia River, while the Monashees lie to the river's west on its southward course from itsBig Bend and are flanked on the west by the basin of theThompson andOkanagan Rivers. There are many named subranges of all four subgroupings, particularly in the Selkirks and Monashees. The southward extension of the Selkirks, Purcells and Monashees into the United States are reckoned to be part of theRocky Mountains and the designation Columbia Mountains is not used there (the Purcells, also, go by the name "Percell Mountains" in the United States). TheSalish andCabinet Mountains south of theKootenai River are essentially part of the same landform, but are officially designated part of the Rocky Mountains in the United States.
To the west of the Monashees and Cariboos, there are three intermediary upland areas which are transitional between the mountain ranges and the plateaus flanking theFraser andThompson Rivers. TheseQuesnel,Shuswap, andOkanagan Highlands are sometimes considered as being part of the neighbouring ranges rather than the plateaus and are often spoken of that way locally but are formally designated as being part of theInterior Plateau. The southernmost extends into Washington, where it is named by the American spelling Okanogan Highland (and was the first-named of these groupings).[31]
TheCascade Range (called theCascade Mountains in Canada) extends fromnorthern California in the United States toBritish Columbia, Canada. It consists of non-volcanic andvolcanic mountains: all of the known historic eruptions in the contiguous United States have been from thevolcanoes of the Cascade Volcanic Arc. The highest peak in the Cascade Range isMount Rainier (14,409 feet (4,392 m)), astratovolcano. The small portion of the Cascade Range in Canada is called the Cascade Mountains or Canadian Cascades, and in its southwestern area is similar in terrain to the area north ofGlacier Peak, known as theNorth Cascades, and its northern and eastern extremities verge on theThompson Plateau in a less rugged fashion than in most other parts of the range. The North Cascades are very different in character from the series of high volcanic stratovolcanoes from Rainier southwards toMount Shasta andLassen Peak, and are more severely alpine and steeply rugged, particularly theSkagit Range. Inland portions of the range are dryland and plateau-like in character, such as theOkanagan Range, which lies along the Cascades' northeastern margin, separated by theSimilkameen River.
TheSierra Nevada forms an inland mountain spine of northern California, extending from the terminus of theCascade Range south ofLassen Peak southwards along the east flank of theCentral Valley of California to theTransverse Ranges, forming a mountain region of complex terrain and varied geology which separates the Central Valley from theGreat Basin to the east. The mean height of the mountain summits in the Sierra Nevada gradually increases from north to south, culminating atMount Whitney (14,505 feet (4,421 m)), the highest point in thecontiguous United States. From east to west, the Sierra is wedge-shaped: the west slope gradually rises and the east slope forms a steepescarpment, particularly so in the southern portion.
The northern Sierra surface rocks are predominantly volcanic, while the southern Sierra graniticbatholith has been sculpted by glaciers into dramaticU-shaped valleys and thin ridges calledarêtes.
TheSierra Madre Occidental mountain range is a southern extension of the Sierra Nevada.[33] The range extends from near the Arizona border down to the Sierra Madre del Sur, along the western mainland of Mexico. The high plateau that is formed by the range is cut by deep river valleys.
TheLaramide belt is on the side of the North American Cordillera most distant from the Pacific Coast Ranges. It is named for theLaramie Mountains of easternWyoming (in turn named forJacques La Ramee, a trapper who disappeared in the Laramie Mountains in 1820 and was never heard from again).[34]
TheBrooks Range includes the northernmost of the major mountain systems of the North American Cordillera, and extends along an east–west axis across northernAlaska from near the northern opening of theBering Strait to the northernYukon Territory. Major subranges include theBritish Mountains andRichardson Mountains, towards their eastern end, and at their farthest west is theDe Long Mountains. The Brooks Range forms the northern flank of the lowerYukon River basin, separating it from Alaska'sNorth Slope region, facing theBeaufort Sea. The Brooks Range is considered part of (or an extension of) theRockies.[35][36][37] South of the Brooks Range are theMackenzie Mountains and theCanadian Rockies.
In theRocky Mountains, the highest peak isMount Elbert inColorado at 14,439 feet (4,401 m) above sea level. The American Rockies rise steeply over theInterior Plains to the east, and over theGreat Basin to the west, and extend south to theRio Grande in New Mexico. The United States definition of the Rockies includes theCabinet andSalish Mountains of Idaho and Montana, whereas their counterparts north of theKootenai River, theColumbia Mountains, are sometimes considered a separate system lying to the west of the hugeRocky Mountain Trench which runs the length of British Columbia.[32]
TheSierra Madre Oriental mountains in eastern Mexico are a southern extension of theRocky Mountains.[37][38] The Sierra Madre Oriental spans about 1,000 km (600 miles). Mexico's Gulf Coastal Plain lies to the east of the range, between the mountains and the Gulf of Mexico coast. The Mexican Plateau lies to the west of the range.
The Nevadan belt runs down the middle of the North American Cordillera. Therefore, the intermontane areas can be divided up into the areas east of the Nevadan belt, and those west of the Nevadan belt.
TheInterior Plateau is the northern continuation of theColumbia Plateau, and covers much of inlandBritish Columbia. TheCariboo Mountains andMonashee Mountains lie to the east, theCanadian Cascades are to the southwest, and theHazelton Mountains andCoast Range to the west and northwest.[39]
Within the Interior plateau, theShuswap Highland consists of a portion of the foothills between theThompson Plateau andBonaparte Plateau on the west, and theMonashee Mountains andCariboo Mountains on the east and northeast.[40]
Also within the Interior plateau, theThompson Plateau forms the southern portion of the Interior Plateau. It is bordered on the south by theCanadian Cascades and on the north by theThompson River.[41]
The Okanagan Highland is the part of the Interior Plateau to the east of the Thompson Plateau, and is bounded by theOkanagan River on the west, theShuswap River on the north, and theKettle River on the east side. The Okanagan Highland is described as being a hilly plateau, and is located in southernBritish Columbia and northernWashington.[42] The Interior Plateau also includes theQuesnel Highland,Fraser Plateau,Nechako Plateau, andMcGregor Plateau.
California'sCentral Valley is a large, flat valley that dominates the central portion ofCalifornia, stretching inland and parallel to thePacific Ocean coast. Its northern half is referred to as theSacramento Valley, and its southern half as theSan Joaquin Valley. The two-halves meet at the hugeSacramento-San Joaquin River Delta of the Sacramento and San Joaquin Rivers, which along with their tributaries drain the majority of the valley and flow intoSan Francisco Bay. The Central Valley covers an area of approximately 22,500 square miles (58,000 km2), making it slightly smaller than the state ofWest Virginia and about 13.7% of California's total area. The Central Valley is 40 to 60 miles (60 to 100 km) wide, with theSierra Nevada to the east and theCoast Ranges to the west.
In northwestern Oregon, the fertileWillamette Valley lies between theOregon Coast Range and theCascades; this depression continues north into Washington as thePuget Trough.
TheGulf of California is a body of water that separates thePeninsular Ranges from theSierra Madre Occidental on theMexican mainland. The Gulf of California is 1,126 km (700 miles) long and 48 to 241 km (30 to 150 miles) wide, with an area of 177,000 km2 (68,000 sq mi), a mean depth of 818.08 m (2,684.0 ft), and a volume of 145,000 km3 (35,000 cu mi).[43]
TheRocky Mountain Trench is a large valley that extends approximately 1,600 km (990 mi) fromFlathead Lake,Montana, to theLiard River, just south of theBritish Columbia–Yukon border nearWatson Lake, Yukon. The trench bottom is 3 to 16 km (2 to 10 miles) wide and ranges from 600 to 900 m (2,000 to 3,000 ft) above sea level. The general orientation of the Trench is almost uniformly pointing north. Some of itstopography has been carved intoglacial valleys, but it is primarily a byproduct offaulting. The Trench separates theRocky Mountains on its east from theColumbia Mountains and theCassiar Mountains on its west. It is up to 25 km (16 miles) wide, if measured peak-to-peak.
For convenience the Rocky Mountain Trench may be divided into northern and southern sections. The dividing point reflects the separation of north and easterly flows to the Arctic Ocean versus south and westerly flows to the Pacific Ocean. A break in the valley system at around 54°N nearPrince George,British Columbia may be used for this purpose. There are three main mountain ranges in the Canadian area named the Rocky Mountains, the Columbia Mountains, and the Coast Mountains.
TheColumbia Plateau is ageologic andgeographic region that lies across parts of theU.S. states ofWashington,Oregon, andIdaho.[44] It is a wideflood basalt plateau between theCascade Range and theRocky Mountains, cut through by theColumbia River. In one of various usages, the term "Columbia Basin" refers to more or less the same area as the Columbia Plateau.[45]
TheBasin and Range province covers most of the state ofNevada and parts of the states ofArizona,California,Idaho,New Mexico,Oregon,Texas,Utah, andWyoming, as well as much of northernMexico. It is an extremely arid region characterized bybasin and range topography.[46]
TheColorado Plateau is an area of high desert located inArizona,New Mexico,Colorado, andUtah, bisected by theColorado River which flows westward through the southern part, and theGreen River which flows south from the northernmost part of the plateau. The Green is a tributary of the Colorado, the confluence being west of Moab, Utah in Canyonlands National Park.[47]
TheMexican Plateau is one of six distinct physiographic sections of theBasin and Range Province, which in turn is part of theIntermontane Plateaus physiographic division. It is a large arid-to-semiaridplateau that occupies much of northern and centralMexico. Averaging 1,825 m (5,988 ft) above sea level, it extends from theUnited States border in the north to theTrans-Mexican Volcanic Belt in the south and is bounded by theSierra Madre Occidental andSierra Madre Oriental to the west and east, respectively.
A low east–west mountain range in the state ofZacatecas divides the plateau into northern and southern sections. These two sections, called the Northern Plateau (Spanish:Mesa del Norte) and Central Plateau (Spanish:Mesa Central), are now generally regarded by geographers as sections of one plateau.
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