Editing Rocky Mountains (section)

==Geology==
{{See also|Geology of the Rocky Mountains}}
The rocks in the Rocky Mountains were formed before the mountains were raised by tectonic forces. The oldest rock is Precambrian [[metamorphic rock]] that forms the core of the North American continent. There is also [[Precambrian]] sedimentary [[argillite]], dating back to 1.7 billion years ago. During the [[Paleozoic]], western North America lay underneath a shallow sea, which deposited many kilometers of [[limestone]] and [[Dolomite (mineral)|dolomite]].<ref name=gadd1>{{cite book|title=Handbook of the Canadian Rockies|first=Ben|last=Gadd|year=1995|publisher=Corax Press|isbn=9780969263111}}</ref>{{rp|76}}
[[File:Jackson Glacier terminus.jpg|thumb|right|Glaciers, such as [[Jackson Glacier]] in [[Glacier National Park (U.S.)|Glacier National Park]], [[Montana]], as shown here, have dramatically shaped the Rocky Mountains.]]
In the southern Rockies, near present-day Colorado, these ancestral rocks were disturbed by mountain building approximately 300 [[Year#SI prefix multipliers|Ma]], during the [[Pennsylvanian (geology)|Pennsylvanian]]. This mountain-building produced the Ancestral Rocky Mountains. They consisted largely of Precambrian metamorphic rock forced upward through layers of the limestone laid down in the shallow sea.<ref>{{cite book|title=Roadside Geology of Colorado|last=Chronic|first=Halka|year=1980|publisher=Mountain Press Publishing Company |isbn=978-0-87842-105-3}}</ref> The mountains eroded throughout the late Paleozoic and early [[Mesozoic Era|Mesozoic]], leaving extensive deposits of [[sedimentary rock]].

[[Terranes]] began colliding with the western edge of North America in the [[Mississippian age|Mississippian]] (approximately 350 million years ago), causing the [[Antler orogeny]].<ref name=Blakely>{{cite web|url=http://jan.ucc.nau.edu/~rcb7/Text_WUS.html|title=Geologic History of Western US|first=Ron|last=Blakely|url-status=live|archive-url=https://web.archive.org/web/20100622013326/http://jan.ucc.nau.edu/~rcb7/Text_WUS.html|archive-date=June 22, 2010}}</ref> For 270 million years, the focus of the effects of plate collisions were near the edge of the North American Plate boundary, far to the west of the Rocky Mountain region.<ref name=Blakely/> It was not until 80 Ma that these effects began reaching the Rockies.<ref name=English>{{cite journal|url=http://web.uvic.ca/~stj/Assets/PDFs/04%20JE%20&%20STJ%20IGR%20Laramide.pdf|first1=Joseph M.|last1=English|first2=Stephen T.|last2=Johnston|title=The Laramide Orogeny: What Were the Driving Forces?|journal=International Geology Review|volume=46|year=2004|pages=833 838|doi=10.2747/0020-6814.46.9.833|issue=9|url-status=live|archive-url=https://web.archive.org/web/20110607041857/http://web.uvic.ca/~stj/Assets/PDFs/04%20JE%20%26%20STJ%20IGR%20Laramide.pdf|archive-date=June 7, 2011|bibcode=2004IGRv...46..833E|s2cid=129901811}}</ref>

The current Rocky Mountains arose in the [[Laramide orogeny]] from between 80 and 55 Ma.<ref name=English/> For the Canadian Rockies, the mountain building is analogous to pushing a rug on a hardwood floor:<ref name=gadd2>{{cite book|title=Canadian Rockies Geology Road Tours|first=Ben|last=Gadd|year=2008|publisher=Corax Press|isbn=9780969263128}}</ref>{{rp|78}} the rug bunches up and forms wrinkles (mountains). In Canada, the terranes and subduction are the foot pushing the rug, the ancestral rocks are the rug, and the [[Canadian Shield]] in the middle of the continent is the hardwood floor.<ref name=gadd2/>{{rp|78}}

Further south, an unusual subduction may have caused the growth of the Rocky Mountains in the United States, where the [[Farallon Plate]] dove at a shallow angle below the [[North American Plate]]. This low angle moved the focus of melting and mountain building much farther inland than the normal {{convert|200|to|300|mi|km|-2|order=flip}}. Scientists hypothesize that the shallow angle of the subducting plate increased the friction and other interactions with the thick continental mass above it. Tremendous [[Thrust fault|thrusts]] piled sheets of crust on top of each other, building the broad, high Rocky Mountain range.<ref name="usgs">{{USGS|url=http://geomaps.wr.usgs.gov/parks/province/rockymtn.html|title=Geologic Provinces of the United States: Rocky Mountains|access-date=December 10, 2006}}</ref>

[[File:Roxborough.jpg|thumb|left|Tilted slabs of sedimentary rock in [[Roxborough State Park]] near [[Denver]]]]
The current southern Rockies were forced upwards through the layers of Pennsylvanian and [[Permian]] sedimentary remnants of the Ancestral Rocky Mountains.<ref>{{cite web|last=Lindsey|first=D.A.|year=2010|url=https://pubs.usgs.gov/circ/1349/pdf/C1349.pdf|title=The geologic story of Colorado's Sangre de Cristo Range|publisher=U.S. Geological Survey|id=Circular 1349|url-status=live|archive-url=https://web.archive.org/web/20170502034033/https://pubs.usgs.gov/circ/1349/pdf/C1349.pdf|archive-date=May 2, 2017}}</ref> Such sedimentary remnants were often tilted at steep angles along the flanks of the modern range; they are now visible in many places throughout the Rockies, and are shown along the [[Dakota Hogback]], an early Cretaceous sandstone formation running along the eastern flank of the modern Rockies.

Just after the Laramide orogeny, the Rockies were like [[Tibetan Plateau|Tibet]]: a high plateau, probably {{Convert|6000|m|ft|-3}} above sea level. In the last sixty million years, [[erosion]] stripped away the high rocks, revealing the ancestral rocks beneath, and forming the current landscape of the Rockies.<ref name=gadd2/>{{rp|80–81}}

Periods of glaciation occurred from the [[Pleistocene]] Epoch (1.8 million – 70,000 years ago) to the [[Holocene]] Epoch (fewer than 11,000 years ago). These ice ages left their mark on the Rockies, forming extensive [[Glacier|glacial]] landforms, such as U-shaped valleys and [[cirque]]s. Recent glacial episodes included the [[Bull Lake Glaciation]], which began about 150,000 years ago, and the [[Pinedale Glaciation]], which perhaps remained at full glaciation until 15,000–20,000 years ago.<ref name="Pierce79">{{cite book|last=Pierce|first=K.L.|year=1979|title=History and dynamics of glaciation in the northern Yellowstone National Park area|id=Professional Paper 729-F|publisher=U.S. Geological Survey|location=Washington, DC|pages=1 90}}</ref>

All of these geological processes exposed a complex set of rocks at the surface. For example, volcanic rock from the [[Paleogene]] and [[Neogene]] periods (66 million – 2.6 million years ago) occurs in the San Juan Mountains and in other areas. Millennia of severe erosion in the [[Wyoming Basin]] transformed intermountain basins into a relatively flat terrain. The [[Tetons]] and other north-central ranges contain folded and faulted rocks of Paleozoic and [[Mesozoic]] age draped above cores of [[Proterozoic]] and [[Archean]] igneous and metamorphic rocks ranging in age from 1.2 billion (e.g., Tetons) to more than 3.3 billion years ([[Beartooth Mountains]]).<ref name="USGS">{{USGS|url=http://biology.usgs.gov/s+t/SNT/noframe/wm146.htm|archive-url=https://web.archive.org/web/20060927145110/http://biology.usgs.gov/s+t/SNT/noframe/wm146.htm|title=Rocky Mountains|archive-date=2006-09-27|work=Status and Trends of the Nation's Biological Resources|first=TJ|last=Stohlgren}}</ref>