Western United States

==Natural geography==
[[File:US west coast physiographic regions map.jpg|thumb|upright|The Western United States is subdivided into three [[United States physiographic region|major physiographic regions]]: the [[Rocky Mountains]] (16–19), the [[Intermontane Plateaus]] (20–22), and the [[Pacific Coast Ranges|Pacific Mountains]] (23–25)]]

Along the [[Pacific Ocean]] coast lie the [[Pacific Coast Ranges|Coast Ranges]], which, while not approaching the scale of the [[Rocky Mountains]], are formidable nevertheless. They collect a large part of the airborne moisture moving in from the ocean. East of the Coast Ranges lie several cultivated fertile [[valley]]s, notably the [[San Joaquin Valley|San Joaquin]] and [[Sacramento Valley|Sacramento]] valleys of [[California]] and the [[Willamette Valley]] of [[Oregon]].

[[File:Zion NP20.jpg|thumb|left|[[Zion National Park]] in southern [[Utah]] is one of five national parks in the state.]]
[[File:Big Sur Coastline.jpg|thumb|left|[[Big Sur]], [[California]]]]
[[File:Mojave vista.jpg|thumb|left|The [[Mojave Desert]] covers much of the [[Southwestern United States]].]]
[[File:Grandcanyon view5.jpg|thumb|left|[[Grand Canyon]], [[Arizona]]]]
Beyond the valleys lie the [[Sierra Nevada (U.S.)|Sierra Nevada]] in the south and the [[Cascade Range]] in the north. [[Mount Whitney]], at {{convert|14505|ft|m}} the tallest peak in the contiguous 48 states, is in the [[Sierra Nevada (U.S.)|Sierra Nevada]]. [[Cascade Range|The Cascades]] are also volcanic. [[Mount Rainier]], a volcano in [[Washington (state)|Washington]], is also over {{convert|14000|ft|m}}. [[Mount St. Helens]], a volcano in [[Cascade Range|the Cascades]], [[1980 eruption of Mount St. Helens|erupted explosively in 1980]]. A major volcanic eruption at [[Mount Mazama]] around 4860 BC formed [[Crater Lake]]. These mountain ranges see heavy precipitation, capturing most of the moisture that remains after the Coast Ranges, and creating a [[rain shadow]] to the east forming vast stretches of arid land. These dry areas encompass much of [[Nevada]], [[Utah]], and [[Arizona]]. The [[Mojave Desert]] and [[Sonoran Desert]] along with other deserts are found here.
[[File:High Desert Twilight-3.jpg|thumb|Red sunset twilight in [[Landers, California|Landers]] in the [[High Desert (California)|High Desert]] region of [[California]]]]
[[File:Oregon High Desert.jpg|thumb|The [[High Desert (Oregon)|High Desert]] region of [[Oregon]]]]
[[File:Feral horses - Pryor Mountain Wild Horse Range - Montana.jpg|thumb|Feral horses in the [[Pryor Mountains]] of Southeast [[Montana]]]]
[[File:Great sand dunes.JPEG|thumb|[[Great Sand Dunes National Park]], [[Colorado]]]]

Beyond the deserts lie the [[Rocky Mountains]]. In the north, they run almost immediately east of the [[Cascade Range]], so that the desert region is only a few miles wide by the time one reaches the Canada–US border. [[Rocky Mountains|The Rockies]] are hundreds of miles wide and run uninterrupted from [[New Mexico]] to [[Alaska]]. The Rocky Mountain Region is the highest overall area of the United States, with an average elevation of above {{convert|4000|ft}}. The tallest peaks of [[Rocky Mountains|the Rockies]], 54 of which are over {{convert|14000|ft}}, are found in central and western [[Colorado]]. East of the Rocky Mountains is the Great Plains, the western portions (for example, the eastern half of Colorado) of which are generally considered to be part of the western United States.

The West has several long rivers that empty into the [[Pacific Ocean]], while the eastern rivers run into the [[Gulf of Mexico]]. The [[Mississippi River]] forms the easternmost possible boundary for the West today. The [[Missouri River]], a tributary of the [[Mississippi River|Mississippi]], flows from its headwaters in the [[Rocky Mountains]] eastward across the [[Great Plains]], a vast [[Poaceae|grassy]] plateau, before sloping gradually down to the forests and hence to the [[Mississippi River|Mississippi]]. The [[Colorado River]] snakes through the [[Mountain states]], at one point forming the [[Grand Canyon]].

The [[Colorado River]] is a major source of water in the Southwest and many dams, such as the [[Hoover Dam]], form reservoirs along it. So much water is drawn for drinking water throughout the West and irrigation in [[California]] that in most years, water from the [[Colorado River]] no longer reaches the [[Gulf of California]]. The [[Columbia River]], the largest river in volume flowing into the [[Pacific Ocean]] from [[North America]], and its tributary, the [[Snake River]], water the Pacific Northwest. The [[Platte River|Platte]] runs through [[Nebraska]] and was known for being a mile (2&nbsp;km) wide but only a half-inch (1&nbsp;cm) deep. The [[Rio Grande]] forms the border between [[Texas]] and [[Mexico]] before turning due north and splitting [[New Mexico]] in half.

According to the [[United States Coast Guard]], "The Western Rivers System consists of the [[Mississippi River|Mississippi]], [[Ohio River|Ohio]], [[Missouri River|Missouri]], [[Illinois River|Illinois]], [[Tennessee River|Tennessee]], [[Cumberland River|Cumberland]], [[Arkansas River|Arkansas]], and [[White River (Arkansas)|White Rivers]] and their tributaries, and certain other rivers that flow towards the [[Gulf of Mexico]]."<ref>{{cite web | title= Inland Aids to Navigation | url= http://uscg.mil/hq/cg3/cg3pcx/publications/auxmanuals/ATON2000StudyGuideSec14Inland.pdf | pages= 14–2 | publisher= [[United States Coast Guard]] | work= Coast Guard Auxiliary: National ATON-CU study guide (Section XIV) | access-date= March 21, 2009 | archive-url= https://web.archive.org/web/20090325111054/http://uscg.mil/hq/cg3/cg3pcx/publications/auxmanuals/ATON2000StudyGuideSec14Inland.pdf | archive-date= March 25, 2009 | url-status= dead }}</ref>  The Ohio River portion of the system includes parts of several Atlantic coastal states, from Georgia to New York.<ref>{{cite web | title= Assessment of Ohio River Water Quality Conditions | url= https://www.nrc.gov/docs/ML1826/ML18264A336.pdf | pages= 10 | publisher= Ohio River Valley Water Sanitation Commission | access-date= September 15, 2020 }}</ref>

===Climate and agriculture===
Most of the public land held by the [[United States Forest Service|U.S. National Forest Service]] and Bureau of Land Management is in the Western states. Public lands account for 25 to 75 percent of the total land area in these states.<ref>{{cite web|url=http://www.wildlandfire.com/docs/2007/western-states-data-public-land.htm|title=Western States Data Public Land Acreage|website=www.wildlandfire.com|access-date=March 7, 2008|archive-url=https://web.archive.org/web/20110727120656/http://www.wildlandfire.com/docs/2007/western-states-data-public-land.htm|archive-date=July 27, 2011|url-status=dead}}</ref>

The climate of the West is [[Semi-arid climate|semi-arid]], yet parts of the region get high amounts of rain or snow. Other parts are true desert which receive less than {{convert|5|in}} of rain per year. The climate is increasingly unstable, and subject to periods of severe drought.<ref name="U.S. Government">{{cite book | title=Climate Change on Wildfire Activity: Hearing Before the Committee on Energy and Natural Resources, United States Senate, One Hundred Tenth Congress, First Session, to Consider Scientific Assessments of the Impacts of Global Climate Change on Wildfire Activity in the United States, September 24, 2007 | publisher=U.S. Government Printing Office | issue=v. 4 | year=2007 | isbn=978-0-16-080173-0 | url=https://books.google.com/books?id=0I5UccaKwYcC&pg=PA13 | access-date=June 3, 2023 | page=13}}</ref>

The seasonal temperatures vary greatly throughout the West. Low elevations on the [[West Coast of the United States|West Coast]] have warm summers and mild winters with little to no snow. The [[Southwestern United States|desert southwest]] has very hot summers and mild winters. While the mountains in the southwest receive generally large amounts of snow. The [[Inland Northwest (United States)|Inland Northwest]] has a [[continental climate]] of warm to hot summers and cold to bitterly cold winters.

Annual rainfall is greater in the eastern portions, gradually tapering off until reaching the Pacific Coast where it increases again. In fact, the greatest annual rainfall in the United States falls in the coastal regions of the [[Pacific Northwest]]. Drought is much more common in the West than the rest of the United States. The driest place recorded in the U.S. is [[Death Valley]], California.<ref>{{cite web|url=http://spothopping.com/death-valley/|title=Death Valley: Hottest, Driest, Lowest (SpotHopping.com)|website=spothopping.com}}</ref> In Western states, drought is closely associated with fire risk, and there have been a number of notable wildfires causing extensive property damage and wildlife [[habitat destruction]]. The Western United States is predicted to experience drought-like conditions for much of the 21st century.<ref name="U.S. Government" />

Violent thunderstorms occur east of the [[Rocky Mountains|Rockies]]. [[Tornado]]es occur every spring on the southern plains, with the most common and most destructive centered on [[Tornado Alley]], which covers eastern portions of the West, ([[Texas]] to [[North Dakota]]), and all states in between and to the east.

Agriculture varies depending on rainfall, irrigation, soil, elevation, and temperature extremes. The arid regions generally support only livestock grazing, chiefly beef cattle. The ''[[Corn Belt|wheat belt]]'' extends from [[Texas]] through [[The Dakotas]], producing most of the wheat and soybeans in the U.S. and exporting more to the rest of the world. Irrigation in the [[Southwestern United States|Southwest]] allows the growth of great quantities of fruits, nuts, and vegetables as well as grain, hay, and flowers. [[Texas]] is a major cattle and sheep raising area, as well as the nation's largest producer of cotton. [[Washington (state)|Washington]] is famous for its apples, and [[Idaho]] for its potatoes. [[California]] and [[Arizona]] are major producers of [[citrus]] crops, however, declining supplies of water, as well as urban sprawl have contributed to a sharp decline in citrus production in Arizona.<ref>{{cite web | last=Henne | first=Sarabeth | title=Arizona citrus squeeze: Pushed by development, costs, citrus shrinks | website=azcentral.com and The Arizona Republic | date=May 25, 2019 | url=https://www.azcentral.com/story/money/business/economy/2019/05/25/arizona-citrus-squeeze-pushed-development-costs-citrus-shrinks/1222155001/ | access-date=June 3, 2023}}</ref> Many varieties of [[New Mexico chile|chile peppers]] are grown in the valleys of [[New Mexico]].<ref>{{Cite web|url=https://cpi.nmsu.edu/|title=Chile Pepper Institute &#124; New Mexico State University|website=cpi.nmsu.edu}}</ref><ref>{{Cite web|url=https://www.newmexico.org/chile/|title=New Mexico: Chile Capital of the World|website=www.newmexico.org}}</ref>

Starting in 1902, Congress passed a series of acts authorizing the establishment of the [[United States Bureau of Reclamation]] to oversee water development projects in seventeen western states.

During the first half of the 20th century, dams and irrigation projects provided water for rapid agricultural growth throughout the West and brought prosperity for several states, where agriculture had previously only been subsistence level. Following [[World War II]], the West's cities experienced an economic and population boom. The population growth, mostly in the [[Southwestern United States|Southwest]] states of [[New Mexico]], [[Utah]], [[Colorado]], [[Arizona]], and [[Nevada]], has strained water and power resources, with water diverted from agricultural uses to major population centers, such as the [[Las Vegas Valley]] and [[Los Angeles]].

===Geology===
Plains make up much of the eastern portion of the West, underlain with sedimentary rock from the Upper [[Paleozoic]], [[Mesozoic]], and [[Cenozoic]] eras. The [[Rocky Mountains]] expose igneous and metamorphic rock both from the [[Precambrian]] and from the [[Phanerozoic]] eon. The Inter-mountain States and [[Pacific Northwest]] have huge expanses of volcanic rock from the [[Cenozoic]] era. [[Salt pan (geology)|Salt flats]] and salt lakes reveal a time when the great inland seas covered much of what is now the West.

The Pacific states are the most geologically active areas in the United States. [[Earthquake]]s cause damage every few to several years in [[California]]. While the [[Pacific states]] are the most volcanically active areas, extinct [[volcano]]es and lava flows are found throughout most of the West.
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