Pacific Coast Ranges: Difference between revisions

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]])<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 furtherfarther 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.

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, 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|access-date = 9 April 2013|doi = 10.1146/annurev.earth.32.101802.120257|url-status = dead|archive-url = https://web.archive.org/web/20140104204050/http://www.geo.arizona.edu/tectonics/Ducea/teaching/Dickinson2004.pdf|archive-date = 4 January 2014}}</ref> 90-8090–80 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–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 book |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 = Geological 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/>