Editing Devils Tower (section)

==Geology==
{{multiple image
|image1 = Devils Tower National Monument geologic cross section.jpg
|image2 = Devils Tower stratigraphic column.jpg
|footer = Geologic cross section (left), and stratigraphic column (right)
|total_width = 440
}}
{{multiple image
|image1 = Devils Tower NP sign Buried Tower.jpg
|image2 = Devils Tower NP sign How Did the Tower Form?.jpg
|footer = National monument markers depicting the [[sedimentary rock]]s in the area (left), and three theories explaining the origin of the [[igneous rock]]s (right)
|total_width = 440
}}
{{multiple image
|image1 = Phonolite Porphyry of Devils Tower in Wyoming in USA - with scale.jpg
|image2 = DevilsTowerCloseupByPhilKonstantin.jpg
|footer = Devils Tower is composed of a [[porphyritic]] [[phonolite]] (left). Close-up view of the columns (right).
|total_width = 440
}}

The landscape surrounding Devils Tower is composed mostly of [[sedimentary rock]]s. The oldest rocks visible in Devils Tower National Monument were laid down in a shallow sea during the [[Triassic]].<ref name=NPSGeo/> This dark red [[sandstone]] and maroon [[siltstone]], interbedded with [[shale]], can be seen along the [[Belle Fourche River]]. [[Redox|Oxidation]] of iron minerals causes the redness of the rocks. This rock layer is known as the [[Spearfish Formation]]. Above the Spearfish Formation is a thin band of white [[gypsum]], called the [[Gypsum Springs Formation]], [[Jurassic]] in age. Overlying this formation is the [[Sundance Formation]].<ref>{{cite journal|journal=[[United States Geological Survey]]|last1=Robinson |first1=Charles |title=Geology of Devils Tower National Monument, USGS Bulletin 1021-I |url=https://pubs.er.usgs.gov/publication/b1021I |publisher=USGS |access-date=14 April 2021 |date=1956|doi=10.3133/b1021I |doi-access=free }}</ref> During the [[Paleocene]] Epoch, 56 to 66 million years ago, the [[Rocky Mountains]] and the [[Black Hills]] were uplifted.<ref name=NPSGeo/>  [[Magma]] rose through the [[Crust (geology)|crust]], intruding into the existing sedimentary rock layers.<ref name=NPSGeo>[http://www.nps.gov/deto/naturescience/geologicformations.htm National Park Service: Devils Tower: Geologic Formations]</ref>

Geologists Carpenter and Russell studied Devils Tower in the late 19th century and came to the conclusion that it was formed by an [[Igneous rock|igneous]] [[Intrusive rock|intrusion]].<ref>{{cite book | url=https://books.google.com/books?id=q84_AAAAIAAJ&dq=carpenter+russell+%22devils+tower%22+igneous&pg=PP20 | title=A Report on the Geology of Devils Tower National Monument | pages=10 |  author=Effinger, William Lloyd | year=1934 | publisher=U.S. Department of the Interior }}</ref> In 1907, geologists [[Nelson Horatio Darton]] and C.C. O'Harra (of the [[South Dakota School of Mines and Technology|South Dakota School of Mines]]) theorized that Devils Tower must be an eroded remnant of a [[laccolith]].<ref name="UT-Chavis-3-018">{{cite web |last1=Chavis |first1=Jason |title=Facts on the Devils Tower in Wyoming |url=https://traveltips.usatoday.com/devils-tower-wyoming-5176.html |publisher=USA Today |access-date=December 22, 2018 |date=March 21, 2018 |archive-date=March 6, 2021 |archive-url=https://web.archive.org/web/20210306050805/https://traveltips.usatoday.com/devils-tower-wyoming-5176.html |url-status=dead }}</ref>

The igneous material that forms the Tower is a [[phonolite]] [[Porphyry (geology)|porphyry]] intruded about 40.5 million years ago,<ref name=Bassett>{{Cite journal| doi = 10.1126/science.134.3487.1373| issn = 0036-8075| volume = 134| issue = 3487| pages = 1373| last = Bassett| first = W.A.| title = Potassium-Argon Age of Devils Tower, Wyoming| journal = Science| date = October 1961| bibcode = 1961Sci...134.1373B| pmid=17807346| s2cid = 3101604}}</ref> a light to dark-gray or greenish-gray igneous rock with conspicuous crystals of white [[feldspar]].<ref>Woolley, A. R. (1987). ''Alkaline Rocks and Carbonatites of the World, Part 1: North and South America''. London, British Museum (Natural History), University of Texas Press, page 126</ref> As the magma cooled, [[hexagon]]al [[columnar jointing|columns]] formed (though sometimes 4-, 5-, and 7-sided columns were possible), up to {{convert|20|ft|m}} wide and {{convert|600|ft|m}} tall.

As rain and snow continue to erode the sedimentary rocks surrounding the Tower's base, more of Devils Tower will be exposed. Nonetheless, the exposed portions of the Tower still experience certain amounts of erosion. Cracks along the columns are subject to water and ice erosion. Portions, or even entire columns, of rock at Devils Tower are continually breaking off and falling. Piles of broken columns, boulders, small rocks, and stones, called [[scree]], lie at the base of the tower, indicating that it was once wider than it is today.<ref name=NPSGeo />

The geologically related [[Missouri Buttes]] are located {{convert|3.5|mi|abbr=on}} northwest of Devils Tower.