Pacific Coast Ranges: Difference between revisions

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'''The''' '''Pacific Coast Ranges''' (officially gazetted as the '''Pacific Mountain System'''<ref>[http://water.usgs.gov/GIS/metadata/usgswrd/XML/physio.xml ''Physiographic regions of the United States'', USGS]</ref> in the [[United States]] but referred to as the Pacific Coast Ranges),<ref>''[https://books.google.com/books?id=V2d12iZkgOwC&pg=PA361 Merriam-Webster's collegiate encyclopedia]'', page 361 (Merriam-Webster, 2000).</ref> are the series of [[mountain range]]s that stretch along the West Coast of [[North America]] from [[Alaska]] south to Northern and Central [[Mexico]]. Although they are commonly thought to be the westernmost mountain range of the continental United States and Canada, the geologically distinct [[Insular Mountains]] of [[Vancouver Island]] lie farther west.

The Pacific Coast Ranges are part of the [[North American Cordillera]] (sometimes known as the Western Cordillera, or in [[Canada]], as the Pacific Cordillera and/or the Canadian Cordillera), which includes the [[Rocky Mountains]], the [[Columbia Mountains]], the [[Interior Mountains]], the [[Interior Plateau]], the [[Sierra Nevada (U.S.)|Sierra Nevada Mountains]], the [[:Category:Mountain ranges of the Great Basin|Great Basin mountain ranges]], and other ranges and various plateaus and basins.

The term ''Coast Range'' is used by the [[United States Geological Survey]] to refer only to the ranges south of the [[Strait of Juan de Fuca]] in [[Washington (state)|Washington]] to the [[California-Mexico border]], and to those west of [[Puget Sound]], the [[Willamette Valley]], and the [[Sacramento Valley|Sacramento]] and [[San Joaquin Valley|San Joaquin]] valleys (the [[California Central Valley]]).

The character of the ranges varies considerably, from the record-setting [[tidewater glacier]]s in the ranges of Alaska, to the rugged Central and [[Southern California]] ranges, the [[Transverse Ranges]] and [[Peninsular Ranges]], in the [[California chaparral and woodlands|chaparral and woodlands]] ecoregioneco-region with [[California oak woodland|Oak Woodland]], [[Chaparral]] shrub forest or [[Coastal sage scrub]]-covering them. The coastline is often seen dropping steeply into the sea with photogenic views. Along the [[British Columbia]] and Alaska coast, the mountains intermix with the sea in a complex maze of [[fjordsfjord]]s, with thousands of islands. Off the Southern California coast the [[Channel Islands of California|Channel Islands]] [[archipelago]] of the [[Santa Monica Mountains]] extends for {{convert|160|mi|km}}.

There are [[coastal plains]] at the mouths of rivers that have punched through the mountains spreading sediments, most notably at the [[Copper River (Alaska)|Copper River]] in Alaska, the [[Fraser River]] in British Columbia, and the [[Columbia River]] between Washington and Oregon. In California: the [[Sacramento River|Sacramento]] and [[San Joaquin River|San Joaquin]] Rivers' [[San Francisco Bay]], the [[Santa Clara River (California)|Santa Clara River's]]'s [[Oxnard Plain]] ''(home to some of the most fertile soil in the world),'' the Los Angeles, San Gabriel, and Santa Ana Rivers' [[Los Angeles Basin]] - {{Snd}}a coastal sediment-filled plain between the peninsular and transverse ranges with sediment in the basin up to 6 miles (10&nbsp;km) deep, and the San Diego River's [[Mission Bay, San Diego, California|Mission Bay]].

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 (meteorology)|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 Region of California|desert regions]].

Omitted from the list below, but often included is the [[Sierra Nevada (U.S.)|Sierra Nevada]], a major mountain range of eastern California that is separated by the [[Central Valley (California)|Central Valley]] over much of its length from the California Coast Ranges and the Transverse Ranges.<ref>{{cite webencyclopedia

| workencyclopedia = Britannica Online Encyclopedia

| accessdateaccess-date = 2007-09-29

On the West coast of North America, the coast ranges and the coastal plain form the margin. Most of the land is made of [[terrane]]s that have been [[Accretion (geology)|accreted]] onto the margin. In the north, the insular belt is an accreted terrane, forming the margin. This belt extends from the [[Wrangellia Terrane]] in Alaska to the Chilliwack group of Canada.<ref name = Townsend2002>{{cite web|title = Northwest Origins|lastlast1 = Townsend|firstfirst1 = Catherine|last2 = Figge|first2 = John|publisher = The Burke Museum|date = 2002|url = http://www.burkemuseum.org/static/geo_history_wa/}}</ref>

A rupture in [[Rodinia]] 750 million years ago formed a passive margin in the eastern Pacific Northwest. The breakup of [[Pangea]] 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.<ref name = Townsend2002/> The timing of the accretion of the insular belt is uncertain, although the closure did not occur until at least 115 million years ago.<ref name = Townsend2002/> Other [[Mesozoic]] terranes that accreted onto the continent include the [[Klamath Mountains]], the [[Sierra Nevada (U.S.)|Sierra Nevada]], and the Guerrero super-terrane of western Mexico.<ref name=Dickinson2004>{{cite journal|title = Evolution of the North American Cordillera|last = Dickinson|first = William|journal = Annual Review of Earth and Planetary Sciences|date = 2004|volume = 32|pages = 13–45|url = http://www.geo.arizona.edu/tectonics/Ducea/teaching/Dickinson2004.pdf|accessdateaccess-date = 9 April 2013|doi = 10.1146/annurev.earth.32.101802.120257|deadurlurl-status = yesdead|archiveurlarchive-url = https://web.archive.org/web/20140104204050/http://www.geo.arizona.edu/tectonics/Ducea/teaching/Dickinson2004.pdf|archivedatearchive-date = 4 January 2014|df = }}</ref> 80 to 9090–80 million years ago the subducting [[Farallon plate]] split and formed the [[Kula Plate]] to the North. This formed an area in what is now Northern California, where the plates converged forming a [[Mélange]]. North of this was the [[Olympic-WallowaOlympic–Wallowa Lineament#Columbia Embayment and KBML|Columbia Embayment]], where the continental margin was east of the surrounding areas.<ref name = Townsend2002/> Many of the major [[batholith]]s date from the late [[Cretaceous]].<ref name = Dickinson2004/> As the [[Laramide Orogeny]] ended around 48 million years ago, the accretion of the [[Siletzia]] terrane began in the Pacific Northwest. This began the volcanic activity in the [[Cascadia subduction zone]], forming the modern [[Cascade Range]], and lasted into the [[Miocene]]. Events here may relate to the [[Mid-Tertiary ignimbrite flare-up|ignimbrite flare-up]] of the southern [[Basin and Range Province|Basin and Range]].<ref name = Humphreys2009>{{cite journalbook |url=https://doi.org/10.1130/MEM204 |doi=10.1130/978-0-8137-2446-1-204.0.v |isbn=9780813712048 |title = Backbone of the Americas: Shallow Subduction, Plateau Uplift, and Ridge and Terrane Collision |chapter=Relation of flat subduction to magmatism and deformation in the Western United States|last = Humphreys|first = Eugene|publisher = GSAGeological Society of America|date = 2009-06-01}}</ref> As extension in the Basin and Range Province slowed by a change in [[North American Plate]] movement circa 7 to 8 Million years ago, rifting began on the [[Gulf of California]].<ref name = Humphreys2009/>

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 the [[Precambrian]] in parts of the [[Little 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 the [[San 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.

*[[Saint Elias Mountains]], southern Alaska, southwestern Yukon, far northwestern [[British Columbia]]

**[[Boundary Ranges]], southeastern Alaska, northwestern [[British Columbia]]

*[[Sargent Icefield]][[File:Harding Icefield 26-1992.jpgjpeg|right|thumbnail|Harding Icefield]]

{{commonsCommons category|Pacific Coast Ranges|<br/>Pacific Coast Ranges}}

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