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110-574: Based on changes in position of ice sheet margins dated via terrestrial cosmogenic nuclides and radiocarbon dating , growth of ice sheets in the southern hemisphere commenced 33,000 years ago and maximum coverage has been estimated to have occurred sometime between 26,500 years ago and 20,000 years ago. After this, deglaciation caused an abrupt rise in sea level. Decline of the West Antarctica ice sheet occurred between 14,000 and 15,000 years ago, consistent with evidence for another abrupt rise in

220-532: A cold reversal caused a replacement of much of the arboreal vegetation with Magellanic moorland and Alpine species. On Isla Grande de Chiloé , Magellanic moorland and closed-canopy Nothofagus forests were both present during the LGM, but the former disappeared by the late LGM. Little is known about the extent of glaciers during Last Glacial Maximum north of the Chilean Lake District . To the north, in

330-414: A crystallized mineral or has a short enough half-life such that it has decayed since nucleosynthesis , but a long enough half-life such that it has built up measurable concentrations. The former includes measuring abundances of Kr and Ar whereas the latter includes measuring abundances of Be, C, and Al. Three types of cosmic-ray reactions can occur once a cosmic ray strikes matter which in turn produce

440-623: A fauna resembling its position in the dry deserts with temperature extremes. The western continental coast of the U.S., just as the East Coast, varies from a colder-to-warmer climate from north to south. Few species live throughout the entire West Coast, however, there are some, including the bald eagle that inhabits both the Alaskan Aleutian Islands and the California Channel Islands . In most of

550-729: A formal measurement of uncalibrated radiocarbon years , counted from 1950). In New Zealand and neighbouring regions of the Pacific, temperatures may have been further depressed during part of the LGM by the world's most recent supervolcanic eruption , the Oruanui eruption , approximately 25,500 years BP. However, it is estimated that during the LGM, low-to-mid latitude land surfaces at low elevation cooled on average by 5.8 °C relative to their present-day temperatures, based on an analysis of noble gases dissolved in groundwater rather than examinations of species abundances that have been used in

660-532: A high-energy cosmic ray interacts with the nucleus of an in situ Solar System atom , causing nucleons (protons and neutrons) to be expelled from the atom (see cosmic ray spallation ). These nuclides are produced within Earth materials such as rocks or soil , in Earth's atmosphere , and in extraterrestrial items such as meteoroids . By measuring cosmogenic nuclides, scientists are able to gain insight into

770-486: A local glacial maximum in the region. In northeastern Italy , in the region around Lake Fimon , Artemisia -dominated semideserts, steppes, and meadow-steppes replaced open boreal forests at the start of the LGM, specifically during Heinrich Stadial 3. The overall climate of the region became both drier and colder. In the Sar Mountains , the glacial equilibrium-line altitude was about 450 metres lower than in

880-410: A mixture of grassland and tundra prevailed, and even here, the northern limit of tree growth was at least 20° farther south than today. In the period before the LGM, many areas that became completely barren desert were wetter than they are today, notably in southern Australia, where Aboriginal occupation is believed to coincide with a wet period between 40,000 and 60,000 years Before Present (BP,

990-414: A myth of the west which has shaped much of American popular culture since the late 19th century. Writers as diverse as Bret Harte and Zane Grey celebrated or derided cowboy culture, while artists such as Frederic Remington created western art as a method of recording the expansion into the west. The American cinema , in particular, created the genre of the western movie , which, in many cases, use

1100-884: A national issue, agencies of the federal government own and manage vast areas of land. (The most important among these are the National Park Service and the Bureau of Land Management within the Interior Department , and the U.S. Forest Service within the Agriculture Department .) National parks are reserved for recreational activities such as fishing , camping , hiking , and boating , but other government lands also allow commercial activities like ranching , logging , and mining . In recent years, some local residents who earn their livelihoods on federal land have come into conflict with

1210-463: A possible shift in the popular understanding of the West as a region in the early 1990s, historian Walter Nugent conducted a survey of three groups of professionals with ties to the region: a large group of Western historians (187 respondents), and two smaller groups, 25 journalists and publishers and 39 Western authors. A majority of the historian respondents placed the eastern boundary of the West east of

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1320-478: A range of geological and astronomical processes. There are both radioactive and stable cosmogenic nuclides. Some of these radionuclides are tritium , carbon-14 and phosphorus-32 . Certain light (low atomic number) primordial nuclides (isotopes of lithium , beryllium and boron ) are thought to have been created not only during the Big Bang , but also (and perhaps primarily) to have been made after

1430-578: A sharp decline in citrus production in Arizona. Many varieties of chile peppers are grown in the valleys of New Mexico . 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

1540-460: A slow change in vegetation towards a sparsely distributed vegetation dominated by Nothofagus species. Within this parkland vegetation Magellanic moorland alternated with Nothofagus forest, and as warming progressed even warm-climate trees began to grow in the area. It is estimated that the tree line was depressed about 1,000 m relative to present day elevations during the coldest period, but it rose gradually until 19,300 years ago. At that time

1650-464: A total 2020 population of 78,588,572. The West is one of the most sparsely settled areas in the United States with 49.5 inhabitants per square mile (19.1 inhabitants/km ). Only Texas with 78.0 inhabitants/sq mi (30.1 inhabitants/km ), Washington with 86.0 inhabitants/sq mi (33.2 inhabitants/km ), and California with 213.4 inhabitants/sq mi (82.4 inhabitants/km ) exceed

1760-754: A volcano in Washington , is also over 14,000 feet (4,300 m). Mount St. Helens , a volcano in the Cascades , 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. Beyond

1870-461: Is exactly the same. These same nuclides still arrive on Earth in small amounts in cosmic rays, and are formed in meteoroids, in the atmosphere, on Earth, "cosmogenically". However, beryllium ( all of it stable beryllium-9) is present primordially in the Solar System in much larger amounts, having existed prior to the condensation of the Solar System, and thus present in the materials from which

1980-489: Is in the Western states. Public lands account for 25 to 75 percent of the total land area in these states. The climate of the West is semi-arid , yet parts of the region get high amounts of rain or snow. Other parts are true desert which receive less than 5 inches (130 mm) of rain per year. The climate is increasingly unstable, and subject to periods of severe drought. The seasonal temperatures vary greatly throughout

2090-689: Is predicted to experience drought-like conditions for much of the 21st century. Violent thunderstorms occur east of the Rockies . Tornadoes 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 wheat belt extends from Texas through The Dakotas , producing most of

2200-631: Is referred to in Britain as the Dimlington Stadial , dated to between 31,000 and 16,000 years ago. The average global temperature about 21,000 years ago was about 6 °C (11 °F) colder than today. According to the United States Geological Survey (USGS), permanent summer ice covered about 8% of Earth's surface and 25% of the land area during the last glacial maximum. The USGS also states that sea level

2310-734: Is the largest region of the country, covering nearly half the land area of the contiguous United States . It is also the most geographically diverse, incorporating geographic regions such as the temperate rainforests of the Northwest , the highest mountain ranges, including the Rocky Mountains , the Sierra Nevada , and the Cascade Range , numerous glaciers , and the western edge of the Great Plains . It also contains

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2420-816: The American West , the Western States , the Far West , the Western territories , and the West ) is one of the four census regions defined by the United States Census Bureau . As American settlement in the U.S. expanded westward , the meaning of the term the West changed. Before around 1800, the crest of the Appalachian Mountains was seen as the western frontier . The frontier moved westward and eventually

2530-673: The Baltic Shield , and in Russia in particular, the LGM ice margin of the Fennoscandian Ice Sheet was highly lobate. The main LGM lobes of Russia followed the Dvina , Vologda and Rybinsk basins respectively. Lobes originated as result of ice following shallow topographic depressions filled with a soft sediment substrate. The northern Ural region was covered in periglacial steppes. Permafrost covered Europe south of

2640-778: The Barents Sea , the Kara Sea , and Novaya Zemlya , ending at the Taymyr Peninsula in what is now northwestern Siberia. Warming commenced in northern latitudes around 20,000 years ago, but it was limited and considerable warming did not take place until around 14,600 year ago. In northwestern Russia , the Fennoscandian ice sheet reached its LGM extent approximately 17,000 years ago, about five thousand years later than in Denmark, Germany and Western Poland. Outside

2750-697: The Big Bang and the Solar System's formation (thus making these primordial nuclides , by definition) are not termed "cosmogenic", even though they were formed by the same process as the cosmogenic nuclides (although at an earlier time). The primordial nuclide beryllium-9, the only stable beryllium isotope, is an example of this type of nuclide. In contrast, even though the radioactive isotopes beryllium-7 and beryllium-10 fall into this series of three light elements (lithium, beryllium, boron) formed mostly by cosmic ray spallation nucleosynthesis , both of these nuclides have half lives too short (53 days and ca. 1.4 million years, resp.) for them to have been formed before

2860-614: The Cantabrian Mountains of the northwestern corner of the Iberian Peninsula , which in the present day have no permanent glaciers, the LGM led to a local glacial recession as a result of increased aridity caused by the growth of other ice sheets farther to the east and north, which drastically limited annual snowfall over the mountains of northwestern Spain. The Cantabrian alpine glaciers had previously expanded between approximately 60,000 and 40,000 years ago during

2970-577: The Cenozoic era. 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. Earthquakes cause damage every few to several years in California . While the Pacific states are the most volcanically active areas, extinct volcanoes and lava flows are found throughout most of

3080-590: The East . During the latter half of the 20th century, several transcontinental interstate highways crossed the West bringing more trade and tourists from the East. Oil boom towns in Texas and Oklahoma rivaled the old mining camps for their rawness and wealth. The Dust Bowl forced children of the original homesteaders even further west. The movies became America's chief entertainment source featuring western fiction , later

3190-693: 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

3300-544: The Gulf of Mexico . The Mississippi River forms the easternmost possible boundary for the West today. The Missouri River , a tributary of the Mississippi , flows from its headwaters in the Rocky Mountains eastward across the Great Plains , a vast grassy plateau, before sloping gradually down to the forests and hence to the Mississippi . The Colorado River snakes through the Mountain states , at one point forming

3410-720: The Gulf of Oman . Bathymetric data suggests there were two palaeo-basins in the Persian Gulf. The central basin may have approached an area of 20,000 km, comparable at its fullest extent to lakes such as Lake Malawi in Africa. Between 12,000 and 9,000 years ago much of the Gulf's floor was not covered by water, only being flooded by the sea after 8,000 years ago. It is estimated that annual average temperatures in Southern Africa were 6 °C lower than at present during

Last Glacial Maximum - Misplaced Pages Continue

3520-615: The Hex River Mountains , in the Western Cape , block streams and terraces found near the summit of Matroosberg evidences past periglacial activity which likely occurred during the LGM. Palaeoclimatological proxies indicate the region around Boomplaas Cave was wetter, with increased winter precipitation. The region of the Zambezi River catchment was colder relative to present and the local drop in mean temperature

3630-703: The Las Vegas Valley and Los Angeles . 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

3740-413: The Mississippi , Ohio , Missouri , Illinois , Tennessee , Cumberland , Arkansas , and White Rivers and their tributaries, and certain other rivers that flow towards the Gulf of Mexico ." The Ohio River portion of the system includes parts of several Atlantic coastal states, from Georgia to New York. Most of the public land held by the U.S. National Forest Service and Bureau of Land Management

3850-529: The Mormon Trail , made its fortunes on outfitting settlers; St. Louis built itself upon the vast fur trade in the West before its settlement. The 1850s were marked by political battles over the expansion of slavery into the western territories, issues leading to the Civil War . Between 1863 and 1869, North America's first transcontinental railroad was constructed to connect the eastern US with

3960-593: The Mountain States include Denver , Colorado Springs , Phoenix , Tucson , Albuquerque , Las Vegas , Reno , Salt Lake City , Boise , El Paso , and Billings . Along the Pacific Ocean coast lie the 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

4070-882: The Northern Mariana Islands ) are sometimes considered part of the Western United States. American Samoa is in Polynesia in the South Pacific Ocean , while Guam and the Northern Mariana Islands are in the Mariana Islands in the western North Pacific Ocean . Guam and the Northern Mariana Islands have district courts within the 9th Circuit , which includes western states such as California and Nevada. (See District Court of Guam and District Court for

4180-634: The Oklahoma panhandle are typically considered to be the Southwest states. Meanwhile, the states of Montana, Idaho, Oregon, and Washington can be considered part of the Northwest or Pacific Northwest . The term West Coast is commonly used to refer to just California, Oregon, Washington, and Alaska, whereas Hawaii is more geographically isolated from the continental U.S. and does not necessarily fit in any of these subregions . The three inhabited Pacific U.S. territories ( American Samoa , Guam and

4290-648: The Pacific Ocean from North America , and its tributary, the Snake River , water the Pacific Northwest. The Platte runs through Nebraska and was known for being a mile (2 km) wide but only a half-inch (1 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

4400-536: The Pacific coast . The resulting railroad connection revolutionized the settlement and economy of the American West by making the transportation of passengers and freight quicker, safer, and cheaper. The history of the American West in the late 19th and early 20th centuries has acquired a cultural mythos in the literature and cinema of the United States. The image of the cowboy , the homesteader , and westward expansion took real events and transmuted them into

4510-554: The Virginia opossum , which occurs throughout California and coastal areas in Oregon and Washington. The North American beaver and mountain beaver live in forested areas of Washington, Oregon and Northern California. The kit fox lives throughout Arizona, New Mexico and Utah, while the gray fox occurs throughout the Western U.S. The Western United States has been populated by Native Americans since at least 11,000 years ago, when

Last Glacial Maximum - Misplaced Pages Continue

4620-516: The dry Andes of Central and the Last Glacial Maximum is associated with increased humidity and the verified advance of at least some mountain glaciers. Montane glaciers in the northern Andes reached their peak extent approximately 27,000 years ago. In northwestern Argentina, pollen deposits record the altitudinal descent of the treeline during the LGM. Amazonia was much drier than in the present. δ D values from plant waxes from

4730-711: The sea level about 14,500 years ago. Glacier fluctuations around the Strait of Magellan suggest the peak in glacial surface area was constrained to between 25,200 and 23,100 years ago. There are no agreed dates for the beginning and end of the LGM, and researchers select dates depending on their criteria and the data set consulted. Jennifer French, an archeologist specialising in the European Palaeolithic, dates its onset at 27,500 years ago, with ice sheets at their maximum by around 26,000 years ago and deglaciation commencing between 20,000 and 19,000 years ago. The LGM

4840-605: The Andes occupying lacustrine and marine basins where they spread out forming large piedmont glacier lobes . Glaciers extended about 7 km west of the modern Llanquihue Lake , but not more than 2 to 3 km south of it. Nahuel Huapi Lake in Argentina was also glaciated by the same time. Over most of the Chiloé Archipelago , glacier advance peaked 26,000 years ago, forming a long north–south moraine system along

4950-427: The Big Bang, but before the condensation of the Solar System, by the process of cosmic ray spallation on interstellar gas and dust. This explains their higher abundance in cosmic dust as compared with their abundances on Earth. This also explains the overabundance of the early transition metals just before iron in the periodic table – the cosmic-ray spallation of iron produces scandium through chromium on

5060-405: The Census definition out on the eastern edge of the Great Plains or on the Mississippi River . The survey respondents as a whole showed just how little agreement there was on the boundaries of the West. The region is split into two smaller units or divisions, by the U.S. Census Bureau: Other classifications distinguish between Southwest and Northwest . Arizona, New Mexico, West Texas , and

5170-433: The Coast Ranges lie several cultivated fertile valleys , notably the San Joaquin and Sacramento valleys of California and the Willamette Valley of Oregon . Beyond the valleys lie the Sierra Nevada in the south and the Cascade Range in the north. Mount Whitney , at 14,505 feet (4,421 m) the tallest peak in the contiguous 48 states, is in the Sierra Nevada . The Cascades are also volcanic. Mount Rainier ,

5280-435: The Great Barrier Reef was enhanced due to low atmospheric CO 2 levels. The deep waters of the Indian Ocean were significantly less oxygenated during the LGM compared to the Middle Holocene. The deep South Indian Ocean in particular was an enormous carbon sink, partially explaining the very low p CO 2 of the LGM. The intermediate waters of the southeastern Arabian Sea were poorly ventilated relative to today because of

5390-491: The Holocene. In Greece , steppe vegetation predominated. Megafaunal abundance in Europe peaked around 27,000 and 21,000 BP; this bountifulness was attributable to the cold stadial climate. In Greenland, the difference between LGM temperatures and present temperatures was twice as great during winter as during summer. Greenhouse gas and insolation forcings dominated temperature changes in northern Greenland, whereas Atlantic meridional overturning circulation (AMOC) variability

5500-432: The LGM are significantly more enriched than those in the present and those dating back to MIS 3, evidencing this increased aridity. Eastern Brazil was also affected; the site of Guanambi in Bahia was much drier than today. AMOC was weaker and more shallow during the LGM. Sea surface temperatures in the western subtropical gyre of the North Atlantic were around 5 °C colder compared to today. Intermediate depth waters of

5610-624: The LGM except in transient intervals around 23,200 and 22,300 BP. In the western South Atlantic , where Antarctic Intermediate Water forms, sinking particle flux was heightened as a result of increased dust flux during the LGM and sustained export productivity. The increased sinking particle flux removed neodymium from shallow waters, producing an isotopic ratio change. On the Island of Hawaii , geologists have long recognized deposits formed by glaciers on Mauna Kea during recent ice ages. The latest work indicates that deposits of three glacial episodes since 150,000 to 200,000 years ago are preserved on

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5720-428: The LGM, 21,000 years ago, the sea level was about 125 meters (about 410 feet) lower than it is today. Across most of the globe, the hydrological cycle slowed down, explaining increased aridity in many regions of the world. In Africa and the Middle East, many smaller mountain glaciers formed, and the Sahara and other sandy deserts were greatly expanded in extent. The Atlantic deep sea sediment core V22-196, extracted off

5830-420: The Last Glacial Maximum. This temperature drop alone would however not have been enough to generate widespread glaciation or permafrost in the Drakensberg Mountains or the Lesotho Highlands . Seasonal freezing of the ground in the Lesotho Highlands might have reached depths of 2 meters or more below the surface. A few small glaciers did however develop during the LGM, in particular in south-facing slopes. In

5940-406: The Laurentide Ice Sheet reached 3.2 km in height around Keewatin Dome and about 1.7-2.1 km along the Plains divide. In addition to the large Cordilleran Ice Sheet in Canada and Montana , alpine glaciers advanced and (in some locations) ice caps covered much of the Rocky and Sierra Nevada Mountains further south. Latitudinal gradients were so sharp that permafrost did not reach far south of

6050-523: The North Atlantic was reduced, as measured by the increased proportion of radiogenic isotopes in neodymium isotope ratios. There is controversy whether upwelling off the Moroccan coast was stronger during the LGM compared to today. Though coccolith size increases in Calcidiscus leptoporus suggest stronger trade winds during the LGM caused there to be increased coastal upwelling of the northwestern coast of Africa, planktonic foraminiferal δC records show upwelling and primary productivity were not enhanced during

6160-464: The North Atlantic were better ventilated during the LGM by Glacial North Atlantic Intermediate Water (GNAIW) relative to its present-day ventilation by upper North Atlantic Deep Water (NADW). GNAIW was nutrient poor compared to present day upper NADW. Below GNAIW, southern source bottom water that was very rich in nutrients filled the deep North Atlantic. Due to the presence of immense ice sheets in Europe and North America, continental weathering flux into

6270-427: The Northern Mariana Islands ). American Samoa, Guam, and the Northern Mariana Islands are also considered part of the western U.S. by the U.S. National Park Service , the Federal Reserve Bank system, FEMA , and the USGS . The population distribution by race in the Western United States (2022): As defined by the United States Census Bureau , the Western region of the United States includes 13 states, with

6380-516: 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. 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

6490-402: The Rockies , 54 of which are over 14,000 feet (4,300 m), 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

6600-414: The Solar System formed. To make the distinction in another fashion, the timing of their formation determines which subset of cosmic ray spallation-produced nuclides are termed primordial or cosmogenic (a nuclide cannot belong to both classes). By convention, certain stable nuclides of lithium, beryllium, and boron are thought to have been produced by cosmic ray spallation in the period of time between

6710-429: The West and California , whites and blacks together are less than half the population because of the preference for the region by Hispanics and Asians . African and European Americans, however, continue to wield a stronger political influence because of the lower rates of citizenship and voting among Asians and Hispanics . According to 2022 estimates from the Census Bureau, the largest ancestries reported in

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6820-440: 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 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

6930-517: The West are Mexican (24.2%), German (10.1%), English (9.5%), Irish (7.2%), Italian (3.5%), Filipino (3.4%), and Chinese (3.3%). The West also contains much of the Native American population in the U.S., particularly in the large reservations in the Mountain and Desert States . As of 2022, the West is home to 365,351 Navajo , 109,208 Apache , and 78,364 Blackfeet , as well as 276,082 people identifying as Indigenous Mexican . The largest concentrations for African-Americans in

7040-453: The West as a metaphor for the virtue of self-reliance and an American ethos. The contrast between the romanticism of culture about the West and the actuality of the history of the westward expansion has been a theme of late 20th and early 21st century scholarship about the West. Cowboy culture has become embedded in the American experience as a common cultural touchstone, and modern forms as diverse as country and western music have celebrated

7150-409: The West can be found in San Diego , Los Angeles , Oakland , Sacramento , Fresno , San Francisco , Seattle , Tacoma , Phoenix , Las Vegas , Denver , and Colorado Springs . The Western United States has a higher sex ratio (more males than females ) than any other region in the United States. Because the tide of development had not yet reached most of the West when conservation became

7260-662: The West. The ecoregions and ecology found in the Western United States are extremely varied. For instance, large areas of land are made up of everything from sand dunes in the Central Basin and Range ecoregion , which makes up much of the State of Nevada , to the ecology of the North Cascades in Washington state , which has the largest concentration of active alpine glaciers in the lower 48 . The densely forested areas found in Northern California , Oregon , Washington, Idaho , and Montana have mostly species adapted to living in temperate climates , while Southern California , Nevada , Arizona , southern Utah , and New Mexico have

7370-444: The West. Low elevations on the West Coast have warm summers and mild winters with little to no snow. The desert southwest has very hot summers and mild winters. While the mountains in the southwest receive generally large amounts of snow. The 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

7480-413: The atmosphere . The massive sheets of ice locked away water, lowering the sea level, exposing continental shelves , joining land masses together, and creating extensive coastal plains . The ice sheets also changed the atmospheric circulation, causing the northern Pacific and Atlantic oceans to cool and produce more clouds, which amplified the global cooling as the clouds reflected even more sunlight. During

7590-571: The atmosphere, but some are formed in situ in soil and rock exposed to cosmic rays, notably calcium-41 in the table below. As seen in the table above, there are a wide variety of useful cosmogenic nuclides which can be measured in soil, rocks, groundwater, and the atmosphere. These nuclides all share the common feature of being absent in the host material at the time of formation. These nuclides are chemically distinct and fall into two categories. The nuclides of interest are either noble gases which due to their inert behavior are inherently not trapped in

7700-571: The best known being Lake Bonneville in Utah . This also occurred in Afghanistan and Iran , where a major lake formed in the Dasht-e Kavir . In Australia , shifting sand dunes covered half the continent, while the Chaco and Pampas in South America became similarly dry. Present-day subtropical regions also lost most of their forest cover, notably in eastern Australia, the Atlantic Forest of Brazil , and southern China , where open woodland became dominant due to much drier conditions. In northern China – unglaciated despite its cold climate –

7810-401: The coast of Senegal, shows a major southward expansion of the Sahara. The Persian Gulf averages about 35 metres in depth and the seabed between Abu Dhabi and Qatar is even shallower, being mostly less than 15 metres deep. For thousands of years the Ur-Shatt (a confluence of the Tigris - Euphrates Rivers ) provided fresh water to the Gulf, as it flowed through the Strait of Hormuz into

7920-653: The community of Hollywood in Los Angeles became the headquarters of the mass media such as radio and television production. California has emerged as the most populous state and one of the top 10 economies in the world. Massive late 19th–20th century population and settlement booms created two megalopolis areas of the Greater Los Angeles / Southern California and the San Francisco Bay Area / Northern California regions, one of

8030-644: The contiguous Western U.S. are mule deer , white-tailed antelope squirrels , cougars , American badgers , coyotes , hawks and several species of snakes and lizards are common. While the American black bear lives throughout the U.S., the brown bears and grizzly bears are more common in the northwest and in Alaska. Along the West Coast there are several species of whales, sea otters , California sea lions , eared seals and northern elephant seals . In

8140-724: The continents: the Indonesian islands as far east as Borneo and Bali were connected to the Asian continent in a landmass called Sundaland . Palawan was also part of Sundaland, while the rest of the Philippine Islands formed one large island separated from the continent only by the Sibutu Passage and the Mindoro Strait . The environment along the coast of South China was not very different from that of

8250-564: 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. 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 4,000 feet (1,200 m). The tallest peaks of

8360-569: The dry, inland desert areas of states such as California, Nevada, Arizona and New Mexico there are some of the world's most venomous lizards, snakes and scorpions. The most notorious might be the Gila monster and Mohave rattlesnake , both found in deserts in the Southwest . The Sonoran Desert has eleven species of rattlesnakes - more than anywhere else in the world. Along the southwestern border there are jaguars and ocelots . Other mammals include

8470-636: The east and west extremities of the Sundaland shelf. Only in Central America and the Chocó region of Colombia did tropical rainforests remain substantially intact – probably due to the extraordinarily heavy rainfall of these regions. Most of the world's deserts expanded. Exceptions were in what is the present-day Western United States , where changes in the jet stream brought heavy rain to areas that are now desert and large pluvial lakes formed,

8580-542: The eastern coast of Chiloé Island (41.5–43° S). By that time the glaciation at the latitude of Chiloé was of ice sheet type contrasting to the valley glaciation found further north in Chile. Despite glacier advances much of the area west of Llanquihue Lake was still ice-free during the Last Glacial Maximum. During the coldest period of the Last Glacial Maximum vegetation at this location was dominated by Alpine herbs in wide open surfaces. The global warming that followed caused

8690-607: The first Paleo-Indians arrived. Pre-Columbian trade routes to kingdoms and empires such as the Mound Builders existed in places such as Yellowstone National Park since around 1000 AD. Major settlement of the western territories developed rapidly in the 1840s, largely through the Oregon Trail and the California Gold Rush of 1849. California experienced such a rapid growth in a few short months that it

8800-421: The formation of the Solar System, and thus they cannot be primordial nuclides. Since the cosmic ray spallation route is the only possible source of beryllium-7 and beryllium-10 occurrence naturally in the environment, they are therefore cosmogenic. Here is a list of radioisotopes formed by the action of cosmic rays ; the list also contains the production mode of the isotope. Most cosmogenic nuclides are formed in

8910-707: The ice sheet down to as far south as present-day Szeged in Southern Hungary. Ice covered the whole of Iceland . In addition, ice covered Ireland along with roughly the northern half of the British Isles with the southern boundary of the ice sheet running approximately from the south of Wales to the north east of England, and then across the now submerged land of Doggerland to Denmark . Central Europe had isolated pockets of relative warmth corresponding to hydrothermally active areas, which served as refugia for taxa not adapted to extremely cold climates. In

9020-420: The ice sheets except at high elevations. Glaciers forced the early human populations who had originally migrated from northeast Siberia into refugia , reshaping their genetic variation by mutation and drift . This phenomenon established the older haplogroups found among Native Americans , and later migrations are responsible for northern North American haplogroups. In southeastern North America, between

9130-433: The land's managers, who are required to keep land use within environmentally acceptable limits. The largest city in the region is Los Angeles , located on the West Coast . Other West Coast cities include San Diego , San Bernardino , San Jose , San Francisco , Oakland , Bakersfield , Fresno , Sacramento , Seattle , Tacoma , Anchorage , and Portland – some of which are dozens of miles inland. Prominent cities in

9240-747: The lands west of the Mississippi River were considered the West . The U.S. Census Bureau's definition of the 13 westernmost states includes the Rocky Mountains and the Great Basin to the Pacific Coast , and the mid-Pacific islands state, Hawaii. To the east of the Western United States is the Midwestern United States and the Southern United States , with Canada to the north and Mexico to

9350-455: The majority of the desert areas located in the United States. The Mojave and the Great Basin deserts lie entirely within the Western region, along with parts of the Sonoran and Chihuahuan deserts (the latter extends significantly into Texas, while both extend into Mexico ). Given this expansive and diverse geography it is no wonder that the region is difficult to define precisely. Sensing

9460-486: The measured cosmogenic nuclides. Since the Earth bulges at the equator and mountains and deep oceanic trenches allow for deviations of several kilometers relative to a uniformly smooth spheroid, cosmic rays bombard the Earth's surface unevenly based on the latitude and altitude. Thus, many geographic and geologic considerations must be understood in order for cosmic-ray flux to be accurately determined. Atmospheric pressure , for example, which varies with altitude, can change

9570-579: The national average of 77.98 inhabitants/sq mi (30.11 inhabitants/km ). As of 2022, just under half of the 78.7 million residents of the West live in California . The entire Western region has also been strongly influenced by European , Hispanic or Latino , Asian and Native Americans ; it contains the largest number of minorities in the U.S. While most of the studies of racial dynamics in America such as riots in Los Angeles have been written about European and African-Americans , in many cities in

9680-486: The one hand and helium through boron on the other. However, the arbitrary defining qualification for cosmogenic nuclides of being formed "in situ in the Solar System" (meaning inside an already aggregated piece of the Solar System) prevents primordial nuclides formed by cosmic ray spallation before the formation of the Solar System from being termed "cosmogenic nuclides"—even though the mechanism for their formation

9790-427: The past. During the Last Glacial Maximum, much of the world was cold, dry, and inhospitable, with frequent storms and a dust-laden atmosphere. The dustiness of the atmosphere is a prominent feature in ice cores; dust levels were as much as 20 to 25 times greater than they are in the present. This was probably due to a number of factors: reduced vegetation, stronger global winds, and less precipitation to clear dust from

9900-650: The persistence of rainforests in eastern Australia at this time. Rivers maintained their sinuous form in southeastern Australia and there was increased aeolian deposition of sediment in compared to today. The Flinders Ranges likewise experienced humid conditions. In southwestern Western Australia, forests disappeared during the LGM. Between Sahul and Sundaland – a peninsula of South East Asia that comprised present-day Malaysia and western and northern Indonesia – there remained an archipelago of islands known as Wallacea . The water gaps between these islands, Sahul and Sundaland were considerably narrower and fewer in number than in

10010-920: The present day, featuring moist subtropical evergreen forests, despite sea levels in the South China Sea being about 100 metres lower than the present day. The Australian mainland, New Guinea , Tasmania and many smaller islands comprised a single land mass. This continent is now referred to sometimes as Sahul . In the Bonaparte Gulf of northwestern Australia, sea levels were about 125 metres lower than present. Interior Australia saw widespread aridity, evidenced by extensive dune activity and falling lake levels. Eastern Australia experienced two nadirs in temperature. Lacustrine sediments from North Stradbroke Island in coastal Queensland indicated humid conditions. Data from Little Llangothlin Lagoon likewise indicate

10120-568: The present day. The two main islands of New Zealand, along with associated smaller islands, were joined as one landmass. Virtually all of the Southern Alps were under permanent ice cover, with alpine glaciers extending from them into much of the surrounding high country . Northern Europe was largely covered by ice, with the southern boundary of the ice sheets passing through Germany and Poland. This ice extended northward to cover Svalbard and Franz Josef Land and northeastward to occupy

10230-557: The present, with flora diminished to almost the same degree as in glaciated areas of Europe and North America. Even in less affected regions, rainforest cover was greatly diminished, especially in West Africa where a few refugia were surrounded by tropical grasslands . The Amazon rainforest was split into two large blocks by extensive savanna , and the tropical rainforests of Southeast Asia probably were similarly affected, with deciduous forests expanding in their place except on

10340-540: The production rate of nuclides within minerals by a factor of 30 between sea level and the top of a 5 km high mountain. Even variations in the slope of the ground can affect how far high-energy muons can penetrate the subsurface. Geomagnetic field strength which varies over time affects the production rate of cosmogenic nuclides though some models assume variations of the field strength are averaged out over geologic time and are not always considered. Western United States The Western United States (also called

10450-503: The sense of isolation and independence of spirit inspired by the frontiersmen on "virgin land". The advent of the automobile enabled the average American to tour the West. Western businessmen promoted Route 66 as a means to bring tourism and industry to the West. In the 1950s, representatives from all the western states built the Cowboy Hall of Fame and Western Heritage Center to showcase western culture and greet travelers from

10560-572: The shutting down of the Oyashio Current and the presence of large east–west mountain ranges were secondary factors that prevented the development of continental glaciation in Asia . All over the world, climates at the Last Glacial Maximum were cooler and almost everywhere drier. In extreme cases, such as South Australia and the Sahel , rainfall could have been diminished by up to 90% compared to

10670-672: The south. The West contains several major biomes , including arid and semi-arid plateaus and plains , particularly in the American Southwest ; forested mountains , including three major ranges, the Sierra Nevada , the Cascades , and Rocky Mountains; the long coastal shoreline of the American Pacific Coast ; and the rainforests of the Pacific Northwest . The Western United States

10780-604: The southern Appalachian Mountains and the Atlantic Ocean, there was an enclave of unusually warm climate. In the Southern Hemisphere, the Patagonian Ice Sheet covered the whole southern third of Chile and adjacent areas of Argentina. On the western side of the Andes the ice sheet reached sea level as far north as in the 41 degrees south at Chacao Channel . The western coast of Patagonia

10890-567: The volcano. Glacial moraines on the volcano formed about 70,000 years ago and from about 40,000 to 13,000 years ago. If glacial deposits were formed on Mauna Loa , they have long since been buried by younger lava flows. Low sea surface temperature (SST) and sea surface salinity (SSS) in the East China Sea during the LGM suggests the Kuroshio Current was reduced in strength relative to the present. Abyssal Pacific overturning

11000-723: The weakened thermohaline circulation. Evidence from sediment cores in the Scotia Sea suggests the Antarctic Circumpolar Current was weaker during the LGM than during the Holocene. The Antarctic Polar Front (APF) was located much farther to the north compared to its present-day location. Studies suggest it could have been placed as far north as 43°S, reaching into the southern Indian Ocean. Cosmogenic nuclide Cosmogenic nuclides (or cosmogenic isotopes ) are rare nuclides ( isotopes ) created when

11110-534: The wheat and soybeans in the U.S. and exporting more to the rest of the world. Irrigation in the 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 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

11220-621: Was a pocket of relative warmth. Following a preceding period of relative retreat from 52,000 to 40,000 years ago, the Laurentide Ice Sheet grew rapidly at the onset of the LGM until it covered essentially all of Canada east of the Rocky Mountains and extended roughly to the Missouri and Ohio Rivers , and eastward to Manhattan , reaching a total maximum volume of around 26.5 to 37 million cubic kilometres. At its peak,

11330-746: Was about 125 meters (410 ft) lower than in present times (2012). When comparing to the present, the average global temperature was 15 °C (59 °F) for the 2013–2017 period. As of 2012 about 3.1% of Earth's surface and 10.7% of the land area is covered in year-round ice. Carbon sequestration in the highly stratified and productive Southern Ocean was essential in producing the LGM. The formation of an ice sheet or ice cap requires both prolonged cold and precipitation ( snow ). Hence, despite having temperatures similar to those of glaciated areas in North America and Europe , East Asia remained unglaciated except at higher elevations. This difference

11440-726: Was admitted to statehood in 1850 without the normal transitory phase of becoming an official territory. One of the largest migrations in American history occurred in the 1840s as the Latter Day Saints left the Midwest to build a theocracy in Utah . Both Omaha, Nebraska and St. Louis, Missouri laid claim to the title, "Gateway to the West" during this period. Omaha , home to the Union Pacific Railroad and

11550-556: Was because the ice sheets in Europe produced extensive anticyclones above them. These anticyclones generated air masses that were so dry on reaching Siberia and Manchuria that precipitation sufficient for the formation of glaciers could never occur (except in Kamchatka where these westerly winds lifted moisture from the Sea of Japan ). The relative warmth of the Pacific Ocean due to

11660-485: Was largely glaciated, but some authors have pointed out the possible existence of ice-free refugia for some plant species. On the eastern side of the Andes, glacier lobes occupied the depressions of Seno Skyring , Seno Otway , Inútil Bay , and Beagle Channel . On the Straits of Magellan, ice reached as far as Segunda Angostura . During the LGM, valley glaciers in the southern Andes (38–43° S) merged and descended from

11770-791: Was seasonally uniform. On the island of Mauritius in the Mascarenhas Archipelago , open wet forest vegetation dominated, contrasting with the dominantly closed-stratified-tall-forest state of Holocene Mauritian forests. There were ice sheets in modern Tibet (although scientists continue to debate the extent to which the Tibetan Plateau was covered with ice) as well as in Baltistan and Ladakh . In Southeast Asia , many smaller mountain glaciers formed, and permafrost covered Asia as far south as Beijing . Because of lowered sea levels, many of today's islands were joined to

11880-567: Was similar in spatial extent. The outflow of North Pacific Intermediate Water through the Tasman Sea was stronger during the LGM. In the Great Barrier Reef along the coast of Queensland , reef development shifted seaward due to the precipitous drop in sea levels, reaching a maximum distance from the present coastline as sea levels approached their lowest levels around 20,700-20,500 years ago. Microbial carbonate deposition in

11990-447: Was the dominant influence on southern Greenland's climate. Illorsuit Island was exclusively covered by cold-based glaciers. Eastern Beringia was extremely cold and dry. July air temperatures in northern Alaska and Yukon were about 2-3 °C lower compared to today. Equilibrium line altitudes in Alaska suggest summer temperatures were 2-5 °C compared to preindustrial. Sediment core analysis from Lone Spruce Pond in southwestern Alaska show it

12100-524: Was weaker during the LGM than in the present day, although it was temporarily stronger during some intervals of ice sheet retreat. The El Niño–Southern Oscillation (ENSO) was strong during the LGM. Evidence suggests that the Peruvian Oxygen Minimum Zone in the eastern Pacific was weaker than it is in the present day, likely as a result of increased oxygen concentrations in seawater permitted by cooler ocean water temperatures, though it

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