Editing Sierra Nevada (section)

==Geologic history==
[[File:Sevehah Cliff.jpg|thumb|Sevehah Cliff, near [[Convict Lake]], shows severely deformed [[Devonian]] rock<ref name=StevensGreene/>]]
[[File:YosemitePark2 amk.jpg|thumb|[[Yosemite Valley]] in Yosemite National Park was carved by glaciers]]
{{anchor|Geology}}
{{For|central Sierra Nevada geology|Geology of the Yosemite area}}

The earliest rocks in the Sierra Nevada are [[Metamorphic rock|metamorphic]] [[roof pendant]]s of [[Paleozoic]] age, the oldest being [[metasediment]]ary rocks from the [[Cambrian]] in the [[Mount Morrison (California)|Mount Morrison]] region.<ref name=StevensGreene>{{cite web |title=Geology of Paleozoic rocks in eastern Sierra Nevada roof pendants, California |url=https://www.researchgate.net/publication/242494245 |first1=CH |last1=Stevens |first2=DC |last2=Greene |year=2000 |publisher=Geological Society of America |id=Field Guide 2}}</ref> These dark-colored [[hornfel]]s, [[slate]]s, [[marble]]s, and [[schist]]s are found in the western foothills (notably around [[Coarsegold, California|Coarsegold]], west of the [[Tehachapi Pass]]) and east of the Sierra Crest.<ref>{{cite web |url=http://pubs.usgs.gov/pp/0385/report.pdf |title=Geology and Mineral Deposits of the Mount Morrison Quadrangle, Sierra Nevada, California |publisher=[[United States Geological Survey]] |access-date=December 12, 2014 |archive-date=September 20, 2015 |archive-url=https://web.archive.org/web/20150920132321/http://pubs.usgs.gov/pp/0385/report.pdf |url-status=live }}</ref> The earliest granite of the Sierra started to form in the [[Triassic]] period. This granite is mostly found east of the crest and north of 37.2°N.<ref name="mesopluto">{{cite web |title=Mesozoic Plutonism in the Sierra Nevada Batholith |url=http://www.colorado.edu/GeolSci/Resources/WUSTectonics/SierraBatholith/mesozoic.htm#pt3 |first=Tanya S. |last=Unger |access-date=June 1, 2010 |archive-url=https://web.archive.org/web/20150923210251/http://www.colorado.edu/GeolSci/Resources/WUSTectonics/SierraBatholith/mesozoic.htm#pt3 |archive-date=September 23, 2015 |url-status=dead}}</ref> In the Triassic and into the [[Jurassic]], an [[island arc]] collided with the west coast of [[North America]] and raised a chain of volcanoes, in an event called the [[Nevadan orogeny]].<ref>{{cite web |url=http://www.gorp.com/parks-guide/travel-ta-yosemite-hiking-california-sidwcmdev_056847.html |archive-url=https://web.archive.org/web/20110424062151/http://www.gorp.com/parks-guide/travel-ta-yosemite-hiking-california-sidwcmdev_056847.html |archive-date=April 24, 2011 |last=Shaffer |first=Jeffrey |title=Evolution of the Yosemite Landscape – The Nevadan Orogeny |work=One Hundred Hikes in Yosemite |url-status=dead}}</ref> Nearly all [[subaerial]] Sierran Arc volcanoes have since disappeared; their remains were redeposited during the [[Great Valley Sequence]] and the subsequent [[Cenozoic]] filling of the Great Valley, which is the source of much of the sedimentary rock in California.

In the [[Cretaceous]], a [[subduction zone]] formed at the edge of the continent.<ref>{{cite web |url=http://jan.ucc.nau.edu/~rcb7/Text_WUS.html |title=Geologic History of Western US |first=Ron |last=Blakely |access-date=June 1, 2010 |archive-date=June 22, 2010 |archive-url=https://web.archive.org/web/20100622013326/http://jan.ucc.nau.edu/~rcb7/Text_WUS.html |url-status=dead}}</ref> This means that an [[oceanic plate]] started to dive beneath the [[North American Plate]]. Magma, formed through the subduction of the ancient [[Farallon Plate]], rose in plumes ([[pluton]]s) deep underground, their combined mass forming what is called the [[Sierra Nevada batholith]]. These plutons formed at various times, from 115&nbsp;[[Megaannum|Ma]] to 87&nbsp;Ma.<ref name="Schoenherr" /> The earlier plutons formed in the western half of the Sierra, while the later plutons formed in the eastern half of the Sierra.<ref name="mesopluto" /> At this time, the Sierra Nevada formed the western ramp of a high plateau to the east, the [[Nevadaplano]].<ref>{{cite journal |last1=Ernst |first1=W. G. |title=Rise and fall of the Nevadaplano |journal=International Geology Review |date=July 1, 2009 |volume=51 |issue=7–8 |pages=583–588 |doi=10.1080/00206810903063315 |bibcode=2009IGRv...51..583E |s2cid=129541879 |url=https://www.tandfonline.com/doi/abs/10.1080/00206810903063315 |issn=0020-6814 |access-date=September 20, 2021 |archive-date=September 20, 2021 |archive-url=https://web.archive.org/web/20210920212209/https://www.tandfonline.com/doi/abs/10.1080/00206810903063315 |url-status=live }}</ref> During this period, rivers cut deep canyons into the range, generating topographic relief similar to the modern Sierra Nevada. This period of incision was halted approximately 30 million years ago by vast outpourings of [[pyroclastic flow]]s from Nevada which filled the northern Sierran valleys with volcanic deposits.<ref>{{Cite journal |last1=Henry |first1=C. D. |last2=Hinz |first2=N. H. |last3=Faulds |first3=J. E. |last4=Colgan |first4=J. P. |last5=John |first5=D. A. |last6=Brooks |first6=E. R. |last7=Cassel |first7=E. J. |last8=Garside |first8=L. J. |last9=Davis |first9=D. A. |last10=Castor |first10=S. B. |date=2012-02-01 |title=Eocene-Early Miocene paleotopography of the Sierra Nevada-Great Basin-Nevadaplano based on widespread ash-flow tuffs and paleovalleys |url=https://pubs.geoscienceworld.org/geosphere/article/8/1/1-27/132491 |journal=Geosphere |language=en |volume=8 |issue=1 |pages=1–27 |doi=10.1130/GES00727.1 |bibcode=2012Geosp...8....1H |issn=1553-040X}}</ref> These pyroclastic flows, which continued for about 10 million years, were followed by andesitic [[lahar]]s which nearly completely buried the northern Sierran landscape such that only the tallest peaks emerged above a volcanic plain.<ref>{{Cite book |last1=Bateman |first1=P.C. |title=Geology of the Sierra Nevada in Geology of Northern California |last2=Wahrhaftig |first2=C. |publisher=California Division of Mines and Geology |year=1966 |pages=107–172}}</ref> This second period of volcanism appears to have been triggered by crustal extension associated with extension of the [[Basin and Range Province]].<ref>{{cite web |title=Basin and Range (Transierra) Region Physical Geography |url=http://www.geog.ucsb.edu/~joel/g148_f09/readings/basin_range/basin_range.html |author=Joel Michaelsen |access-date=May 7, 2010 |url-status=dead |archive-url=https://web.archive.org/web/20110727072611/http://www.geog.ucsb.edu/~joel/g148_f09/readings/basin_range/basin_range.html |archive-date=July 27, 2011}}</ref> As this andesitic volcanism began waning about five million years ago, the rivers were able to begin eroding away the 100s of meters of volcanic deposits and resume the incision that had been halted by the first period of volcanism.

Some studies have argued that this recent incision is a sign of recent tectonic uplift.<ref>{{Cite journal |last=Wakabayashi |first=J. |title=Paleochannels, stream incision, erosion, topographic evolution, and alternative explanations of paleoaltimetry, Sierra Nevada, California |journal=Geosphere |volume=9 |pages=191–215|year=2013|issue=2 |doi=10.1130/GES00814.1|bibcode=2013Geosp...9..191W |doi-access=free }}</ref><ref>{{cite journal|first1=Helen W|last1=Beeson|first2=Scott W|last2=McCoy|title=Disequilibrium river networks dissecting the western slope of the Sierra Nevada, California, USA, record significant late Cenozoic tilting and associated surface uplift|journal=GSA Bulletin|year=2022|volume=134|issue=11–12|pages=2809–2853|doi=10.1130/B35463.1|bibcode=2022GSAB..134.2809B }}</ref> Other geologists claim that the elevations of many of the modern rivers flowing down the range are only {{convert|100|–|300|meters|feet|sigfig=1}} lower than their ancient counterparts from 30–40&nbsp;million years ago and the overall elevation and bedrock topography of the northern Sierra Nevada has changed little since at least 30–40&nbsp;million years ago.<ref>{{cite journal|last1=Mulch|first1=Andreas|first2=Stephan A|last2=Graham|first3=C. Page|last3=Chamberlain|title=Hydrogen isotopes in Eocene river gravels and paleoelevation of the Sierra Nevada.|journal=Science|volume=313|issue=5783|year=2006|pages=87–89|doi=10.1126/science.1125986 |pmid=16825568 |bibcode=2006Sci...313...87M }}</ref><ref>{{Cite journal |last1=Gabet |first1=E.J. |last2=Miggins |first2=D. |date=2020 |title=Minimal net incision of the northern Sierra Nevada (California, USA) since the Eocene-early Oligocene |url=https://doi.org/10.1130/G47902.1 |journal=Geology |volume=48 |issue=10 |pages=1023–1027|doi=10.1130/G47902.1 |bibcode=2020Geo....48.1023G }}</ref><ref>{{Cite journal |last1=Cassel |first1=E.J. |last2=Graham |first2=S.A. |last3=Chamberlain |first3=C.P. |title=Cenozoic tectonic and topographic evolution of the northern Sierra Nevada, California, through stable isotope paleoaltimetry in volcanic glass |journal=Geology |date=2009 |volume=37 |issue=6 |pages=547–550|doi=10.1130/G25572A.1 |bibcode=2009Geo....37..547C }}</ref>

About 2.5&nbsp;Ma, the Earth's climate cooled, and [[ice age]]s started. [[Glacier]]s carved out characteristic U-shaped canyons throughout the Sierra. The combination of river and glacier erosion exposed the uppermost portions of the plutons emplaced millions of years before, leaving only a remnant of [[metamorphic rock]] on top of some Sierra peaks.

Extension of the Basin and Range continues today, leading to downdropping of crustal blocks just east of the Sierra Nevada during large earthquakes, such as the [[1872 Lone Pine earthquake|Lone Pine earthquake]] of 1872.<ref>{{cite web |url=http://sierranevadavirtualmuseum.com/docs/galleries/nathist/geology/lonepine.htm |archive-url=https://web.archive.org/web/20110522015222/http://sierranevadavirtualmuseum.com/docs/galleries/nathist/geology/lonepine.htm |archive-date=May 22, 2011 |title=1872 Lone Pine Earthquake |work=Sierra Nevada Virtual Museum |access-date=May 31, 2010 |quote=Few people ever see a mountain range grow, but on March 26, 1872, the 300 residents of Lone Pine, California, did. |url-status=dead}}</ref>
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{{Wide image|SierraEscarpmentCA.jpg|700px|Sierra Escarpment viewed from the east. In the foreground is [[Tinemaha Reservoir]] in the [[Owens Valley]].}}