Geography of the United States
United Statesis a nation in the Western Hemisphere. It consists of forty-eight contiguous states on the North American continent; Alaska, an enormous peninsulawhich forms the northwestern most part of North America, and Hawaii, an archipelagoin the Pacific Ocean. It also holds several United States territories in the Pacific & Caribbean. The country shares land borders with Canadaand Mexicoand a water border with Russia.
By total area including water, the United States is either slightly larger or smaller than the
People's Republic of China, making it the world's third or fourth largest country. Its rank depends on whether one includes two territories claimed by Indiabut governed by China when calculating China's size. Both China and the United States follow behind Canadaand Russiain total area, and are followed by Brazil. By land area (exclusive of waters), the United States is the world's third largest country, following Russia and China. [Yahoo's chart of countries by land area based on the CIA World Factbook http://education.yahoo.com/reference/factbook/countrycompare/area/3d.html;_ylt=As1XMsN8kgSx746VWazy_s7PecYF] In total area, the United States is:
*three-tenths the size of
*half the size of
*half the size of
*roughly the same size as
*slightly larger than
*slightly more than one and a quarter times the size of
*two and a half times the size of
*roughly 14 times the size of
*roughly 39 times the size of the
NOTE: The US has made numerous major changes to it territorial extent. From the initial publishing of the CIA Factboook to 1996, its listed total area is around 9,372,610 km². But from 1997 to 2007, its listed total area is "upgraded" to around 9,629,091 km². Finally in 2008, US total area has been further "upgraded" to its current 9,800,000 km² figure. For more detail, visit http://www.theodora.com/wfb/abc_world_fact_book.html
The United States shares land borders with
Canada(to the north) and Mexico(to the south), and a territorial water border with Russiain the northwest. The contiguous forty-eight states are otherwise bounded by the Pacific Oceanon the west, the Atlantic Oceanon the east, and the Gulf of Mexicoto the southeast. Alaska borders the Pacific Oceanto the south, the Bering Straitto the west, and the Arctic Oceanto the north, while Hawaiilies far to the southwest of the mainland in the Pacific Ocean.
Forty-eight of the States are in the single region between Canada and Mexico; this group is referred to, with varying precision and formality, as the "continental" or "contiguous" "United States", and as the "
Lower 48". Alaska, which is not included in the term "contiguous United States", is at the northwestern end of North America, separated from the Lower 48 by Canada. The State of Hawaiiis an archipelagoin the Pacific Ocean. The capital city, Washington, District of Columbia, is a federal district located on land donated by the state of Maryland. ( Virginiahad also donated land, but it was returned in 1847.) The United States also have overseas territories with varying levels of independence and organization.
In total area (including inland water),
Russiaand Canada are larger than the United States. Ranking for third-largest status is disputed. Some sources (including " Encyclopædia Britannica" and all publications of the People's Republic of China), list China as larger than the U.S. Many other sources list the U.S. as larger. The dispute appears to hinge on Taiwan, without which China takes fourth place. Total U.S. area is 3,718,711 square miles (9,631,418 km²), of which land is 3,537,438 square miles (9,161,923 km²) and water is 181,273 square miles (469,495 km²). Ranked by land area, the top countries in order are Russia, China, the U.S., and Canada.
The eastern United States has a varied topography. A broad, flat coastal plain lines the Atlantic and Gulf shores from the Texas-Mexico border to New York City, and includes the Florida peninsula. Areas further inland feature rolling hills and temperate forests. The
Appalachian Mountainsform a line of low mountains separating the eastern seaboard from the Great Lakes and the Mississippi Basin. The five Great Lakesare located in the north-central portion of the country, four of them forming part of the border with Canada. The southeast United States contain subtropical forests and, near the gulf coast, mangrovewetlands, especially in Florida. West of the Appalachians lies the Mississippi Riverbasin and two large eastern tributaries, the Ohio Riverand the Tennessee River. The Ohio and Tennessee Valleys and the Midwest consist largely of rolling hills and productive farmland, stretching south to the Gulf Coast.
Great Plainslie west of the Mississippi River and east of the Rocky Mountains. A large portion of the country's agricultural products are grown in the Great Plains. Before their general conversion to farmland, the Great Plains were noted for their extensive grasslands, from tallgrass prairiein the eastern plains to shortgrass steppe in the western High Plains. Elevation rises gradually from less than a few hundred feet near the Mississippi River to more than a mile high in the High Plains. The generally low relief of the plains is broken in several places, most notably in the Ozark and Ouachita Mountains, which form the U.S. Interior Highlands, the only major mountainous region between the Rocky Mountainsand the Appalachian Mountains. [cite web | url=http://www.srs.fs.usda.gov/4106/about/HotSpringsOffice.htm | title= Managing Upland Forests of the Midsouth| publisher= United States Forestry Service | accessdate=2007-10-13] [cite web | url=http://tapestry.usgs.gov/physiogr/physio.html| title= A Tapestry of Time and Terrain: The Union of Two Maps - Geology and Topography| publisher= United States Geological Survey | accessdate=2007-10-13] The Great Plains come to an abrupt end at the Rocky Mountains. The Rocky Mountains form a large portion of the Western U.S., entering from Canadaand stretching nearly to Mexico. The Rocky Mountains generally contain fairly mild slopes and low peaks compared to many of the other great mountain ranges, with a few exceptions (such as the Teton Mountainsin Wyomingand the Sawatch Rangein Colorado). In addition, instead of being one generally continuous and solid mountain range, it is broken up into a number of smaller, intermittent mountain ranges, forming a large series of basins and valleys.
West of the Rocky Mountains lies the
Intermontane Plateaus(also known as the Intermountain West), a large, arid desert lying between the Rockies and the Cascades and Sierra Nevada ranges. The large southern portion, known as the Great Basin, consists of salt flats, drainage basins, and many small north-south mountain ranges. The Southwest is predominantly a low-lying desert region. A portion known as the Colorado Plateau, centered around the Four Cornersregion, is considered to have some of the most spectacular scenery in the world. It is accentuated in such national parks as Grand Canyon, Arches, and Bryce Canyon, among others.
The Grand Canyonfrom Moran Point. The Grand Canyon is among the most famous locations in the country.]
The Intermontane Plateaus come to an end at the
Cascade Rangeand the Sierra Nevada. The Cascades consist of largely intermittent, volcanic mountains rising prominently from the surrounding landscape. The Sierra Nevada, further south, is a high, rugged, and dense mountain range. It contains the highest point in the contiguous 48 states, Mount Whitney(14,505 ft; 4,421 m). These areas contain some spectacular scenery as well, as evidenced by such national parks as Yosemite and Mount Rainier. West of the Cascades and Sierra Nevada is a series of valleys, such as the Central Valley in Californiaand the Willamette Valleyin Oregon. Along the coast is a series of low mountain ranges known as the Pacific Coast Ranges. Much of the Pacific Northwestcoast is inhabited by some of the densest vegetation outside of the Tropics, and also the tallest trees in the world (the Redwoods). Alaskacontains some of the most dramatic and untapped scenery in the country. Tall, prominent mountain ranges rise up sharply from broad, flat tundra plains. On the islands off the south and southwest coast are many volcanoes. Hawaii, far to the south of Alaskain the Pacific Ocean, is a chain of tropical, volcanic islands, popular as a tourist destination for many from East Asiaand the mainland United States.
The geography of the United States varies across their immense area. Within the contential U.S., eight distinct physiographic divisions exist, though each is composed of several smaller physiographic subdivisions. [cite web | title = Physiographic Regions | publisher =
United States Geological Survey| date = 2003-04-17| url = http://tapestry.usgs.gov/physiogr/physio.html | accessdate = 2008-01-30 ] These major divisions are:
Laurentian Upland- part of the Canadian Shieldthat extends into the northern United States Great Lakes area.
Atlantic Plain- the coastal regions of the eastern and southern parts includes the continental shelf, the Atlantic Coast and the Gulf Coast.
Appalachian Highlands- lying on the eastern side of the United States, it includes the Appalachian Mountains, Adirondacksand New Englandprovince.
Interior Plains- part of the interior contentintal United States, it includes much of what is called the Great Plains.
Interior Highlands- also part of the interior contentintal United States, this division includes the OzarkPlateau.
* Rocky Mountain System - one branch of the Cordilleran system lying far inland in the western states.
* Intermontane Plateaus - also divided into the
Columbia Plateau, the Colorado Plateauand the Basin and Range Province, it is a system of plateaus, basins, ranges and gorges between the Rocky and Pacific Mountain Systems. It is the setting for the Grand Canyon, the Great Basinand Death Valley.
* Pacific Mountain System - the coastal mountain ranges and features in the west coast of the United States.
time) that it has since then been very generally reduced to moderate or low relief. It owes its present day altitude either to renewed elevations along the earlier lines or to the survival of the most resistant rocks as residual mountains. The oblique trend of this coast would be even more pronounced but for a comparatively modern crustal movement, causing a depression in the northeast resulting in an encroachment of the sea upon the land. Additionally, the southeastern section has undergone an elevation resulting in the advance of the land upon the sea.
The following map, known as a physiographical map, shows geographical and
terraininformation about the regions of the contiguous 48 states of the U.S. used by earth scientists. The map indicates the age of the exposed surface as well as the type of terrain. More information about the regions is covered in several sub articles found in the additional topics subsection below.
While the Atlantic coast is relatively low, the Pacific coast is, with few exceptions, hilly or mountainous. This coast has been defined chiefly by geologically recent crustal deformations, and hence still preserves a greater relief than that of the Atlantic.
The low Atlantic coast and the hilly or mountainous Pacific coast foreshadow the leading features in the distribution of mountains within the United States. The east coast Appalachian system, originally forest covered, is relatively low and narrow and is bordered on the southeast and south by an important coastal plain. The Cordilleran system on the western side of the continent is lofty, broad and complicated having two branches, the Rocky Mountain System and the Pacific Mountain System. In between these, lie the Intermontaine Plateaus. Heavy forests cover the northwest coast, but elsewhere trees are found only on the higher ranges below the Alpine region. The
intermontanevalleys, plateaus and basins range from treeless to desert with the very arid region being in the southwest.
Columbia Riverand Colorado Riverrise far inland near the easternmost members of the Cordilleran system, and flow through plateaus and intermontaine basins to the ocean.
The Laurentian Highlands, the Interior Plains and the Interior Highlands lie between the two coasts, stretching from the
Gulf of Mexiconorthward, far beyond the national boundary, to the Arctic Ocean. The central plains are divided by a hardly perceptible height of land into a Canadian and a United States portion. It is from the United States side, that the great Mississippi system discharges southward to the Gulf of Mexico. The upper Mississippi and some of the Ohio basin is the semi-arid prairie region, with trees originally only along the watercourses. The uplands towards the Appalachians were included in the great eastern forested area, while the western part of the plains has so dry a climate that its native plant life is scanty, and in the south it is practically barren.
List of North American deserts
Death Valley, Inyo County, California282 feet below sea level(-86 m)
Mount McKinley, Denali Borough, Alaska20,320 feet above sea level (+6,194 m)
Due to its large size and wide range of geographic features, the United States contains examples of nearly every global climate. The climate is temperate in most areas, tropical in
Hawaiiand southern Florida, polar in Alaska, semiarid in the Great Plainswest of the 100th meridian, Mediterranean in coastal Californiaand arid in the Great Basin. Its comparatively generous climate contributed (in part) to the country's rise as a world power, with infrequent severe drought in the major agricultural regions, a general lack of widespread flooding, and a mainly temperate climate that receives adequate precipitation.
The main influence on U.S. weather is the polar jet stream, which brings in large low pressure systems from the northern
Pacific Ocean. The Cascade Range, Sierra Nevada, and Rocky Mountainspick up most of the moisture from these systems as they move eastward. Greatly diminished by the time they reach the High Plains, much of the moisture has been sapped by the orographic effect as it is forced over several mountain ranges. However, once it moves over the Great Plains, uninterrupted flat land allows it to reorganize and can lead to major clashes of air masses. In addition, moisture from the Gulf of Mexicois often drawn northward. When combined with a powerful jet stream, this can lead to violent thunderstorms, especially during spring and summer. Sometimes during late winter and spring these storms can combine with another low pressure system as they move up the East Coast and into the Atlantic Ocean, where they intensify rapidly. These storms are known as Nor'easters and often bring widespread, heavy snowfall to the Mid-Atlantic and New England. The uninterrupted flat grasslands of the Great Plainsalso leads to some of the most extreme climate swings in the world. Temperatures can rise or drop rapidly and winds can be extreme, and the flow of heat waves or Arctic air masses often advance uninterrupted through the plains.
Great Basinand Columbia Plateau(the Intermontane Plateaus) are arid or semiarid regions that lie in the rain shadow of the Cascades and Sierra Nevada. Precipitation averages less than 15 inches (38 cm). The Southwest is a hot desert, with temperatures exceeding 100°F (38°C) for several weeks at a time in summer. The Southwest and the Great Basin are also affected by the monsoonfrom the Gulf of Californiafrom July-September, which brings localized but often severe thunderstorms to the region.
Californiaconsists of a Mediterranean climate, with sometimes excessive rainfall from October-April and nearly no rain the rest of the year. In the Pacific Northwestrain falls year-round, but is much heavier during winter and spring. The mountains of the west receive abundant precipitation and very heavy snowfall. The Cascades are one of the snowiest places in the world, with some places averaging over 600 inches (1,520 cm) of snow annually, but the lower elevations closer to the coast receive very little snow. Another significant (but localized) weather effect is lake-effect snowthat falls south and east of the Great Lakes, especially in the hilly portions of the Upper Peninsulaof Michiganand on the Tug Hill Plateauin New York.The lake effect dumped well over 5 feet of snow in the Buffalo, New York area throughout the 2006-2007 winter The Wasatch Frontand Wasatch Rangein Utahcan also receive significant lake effect accumulations off of the Great Salt Lake.
In northern Alaska,
tundraand arcticconditions predominate, and the temperature has fallen as low as minus 80 °F (−62 °C). [Williams, Jack [http://www.usatoday.com/weather/wcstates.htm Each state's low temperature record] , "USA today", "URL accessed 13 June, 2006."] On the other end of the spectrum, Death Valley, California once reached 134 °F (56.7 °C), the second-highest temperature ever recorded on Earth.cite web | url = http://www.nps.gov/deva/planyourvisit/upload/Weather.pdf | title = Weather and Climate | accessmonthday = October 5 | accessyear = 2006 | year = 2002 | month = January | format = PDF | work = Official website for Death Valley National Park | publisher = National Park Service U. S. Department of the Interior | pages = 1-2]
On average, the mountains of the western states receive the highest levels of snowfall on Earth. The greatest annual snowfall level is at
Mount Rainierin Washington, at 692 inches (17,580 mm); the record there was 1,122 inches (28,500 mm) in the winter of 1971–72. This record was broken by the Mt. Baker Ski Area in northwestern Washington which reported 1,140 inches of snowfall for the 1998-99 snowfall season. Other places with significant snowfall outside the Cascade Range are the Wasatch Mountains, near the Great Salt Lake, and the Sierra Nevada, near Lake Tahoe. In the east, while snowfall does not approach western levels, the region near the Great Lakes and the mountains of the Northeast receive the most. Along the northwestern Pacific coast, rainfall is greater than anywhere else in the continental U.S., with Quinault Rangerin Washington having an average of 137 inches (3480 mm). [National Atlas, [http://www.nationalatlas.gov/mld/prism0p.html Average Annual Precipitation, 1961-1990] , "URL accessed 15 June 2006."] Hawaii receives even more, with 460 inches (11,680 mm) measured annually on Mount Waialeale, in Kauai. The Mojave Desert, in the southwest, is home to the driest locale in the U.S. Yuma, Arizona, has an average of 2.63 inches (66.8 mm) of precipitation each year. [Hereford, Richard, et al, [http://pubs.usgs.gov/fs/fs117-03/ Precipitation History of the Mojave Desert Region, 1893–2001] , "U.S. Geological Survey, Fact Sheet 117-03", "URL accessed 13 June 2006."]
In central portions of the U.S.,
tornadoes are more common than anywhere else on Earth [NOVA, [http://www.pbs.org/wgbh/nova/tornado/country.html Tornado Heaven] , "Hunt for the Supertwister", "URL accessed 15 June 2006."] and touch down most commonly in the spring and summer. Deadly and destructive hurricanes occur almost every year along the Atlantic seaboard and the Gulf of Mexico. The Appalachian region and the Midwest experience the worst floods, though virtually no area in the U.S. is immune to flooding. The Southwest has the worst droughts; one is thought to have lasted over 500 years and to have decimated the Anasazipeople. [O'Connor, Jim E. and John E. Costa, [http://pubs.usgs.gov/circ/2003/circ1245/ Large Floods in the United States: Where They Happen and Why] , "U.S. Geological Survey Circular 1245", "URL accessed 13 June 2006."] The West is affected by large wildfires each year.
The United States is affected by a large variety of natural disasters yearly. Although severe drought is rare, it has occasionally caused major problems, such as during the
Dust Bowl(1931-1942), which coincided with the Great Depression. Farmland failed throughout the Plains, entire regions were virtually depopulated, and dust storms ravaged the land. More recently, the western U.S. experienced widespread drought from 1999-2004, and signs of a major, long-term drought across the Great Plainshave developed. [http://wwwa.accuweather.com/promotion.asp?dir=aw&page=dustbowl] In the past year, drought has spread from the Southern Plains westward through the Southwest and east along the Gulf Coast to Florida.
The United States also experience, by a large margin, the most frequent and powerful
tornadoes in the world. The Great Plains and Midwest, due to the contrasting air masses, sees frequent severe thunderstorms and tornado outbreaks during spring and summer. The strip of land from north Texasnorth to Kansasand east into Tennesseeis known as Tornado Alley, where many houses have tornado shelters and many towns have tornado sirens. Another natural disaster that frequents the country are hurricanes, which can hit anywhere along the Gulf Coast or the Atlantic Coastas well as Hawaiiin the Pacific Ocean. Particularly at risk are the central and southern Texascoasts, the area from southeastern Louisianaeast to the Florida Panhandle, the east coast of Florida, and the Outer Banksof North Carolina, although any portion of the coast could be struck. Hurricane season runs from June 1 to November 30, with a peak from mid-August through early October. Some of the more devastating hurricanes have included the Galveston Hurricane of 1900, Hurricane Andrewin 1992, and Hurricane Katrinain 2005. The remnants of tropical cyclones from the Eastern Pacific also occasionally impact the southwestern United States, bringing sometimes heavy rainfall.
Like drought, widespread severe flooding is rare. Some exceptions include the
Great Mississippi Flood of 1927, the Great Flood of 1993, and widespread flooding and mudslides caused by the 1982-1983 El Niño event in the western United States. Localized flooding can, however, occur anywhere, and mudslides from heavy rain can cause problems in any mountainous area, particularly the Southwest. Large stretches of desert shrub in the west can fuel the spread of wildfires. The narrow canyons of many mountain areas in the west and severe thunderstorm activity during the monsoonseason in summer leads to sometimes devastating flash floods as well, while Nor'Easter snowstorms can bring activity to a halt throughout the Northeast (although heavy snowstorms can occur almost anywhere).
The West Coast of the continental United States and areas of Alaska (including the
Aleutian Islands, the Alaskan Peninsulaand southern Alaskan coast) make up part of the Pacific Ring of Fire, an area of heavy tectonic and volcanic activity that is the source of 90% of the world's earthquakes. The American Northwest sees the highest concentration of active volcanoes in the United States, in Washington, Oregonand northern Californiaalong the Cascade Mountains. There are several active volcanoes located in the islands of Hawaii, including Kilauea in ongoing eruption since 1983, but they do not typically adversely affect the inhabitants of the islands. There has not been a major life-threatening eruption on the Hawaiian islands since the 17th century. Volcanic eruptions can occasionally be devastating, such as in the 1980 eruption of Mount St. Helensin Washington.
The Ring of Fire makes
Californiaand southern Alaskaparticularly vulnerable to earthquakes. Earthquakes can cause extensive damage, such as the 1906 San Francisco Earthquakeor the 1964 Good Friday Earthquakenear Anchorage, Alaska. California is well known for seismic activity, and requires large structures to be earthquake resistantto minimize loss of life and property. Outside of devastating earthquakes, California experiences minor earthquakes on a regular basis.
Other natural hazards include: tsunamis around Pacific Basin, mud slides in
California, forest fires in the west, and permafrost in northern Alaska, a major impediment to development.
The United States holds many areas for the use and enjoyment of the public. These include National Parks, National Monuments,
National Forests, Wilderness areas, and other areas. For lists of areas, see the following articles:
List of U.S. National Parks
List of U.S. National Forests
List of U.S. wilderness areas
List of miscellaneous U.S. public areas
Counties of the United States
Extreme points of the United States
Geographic centers of the United States
Geography of Puerto Rico
Geography of the Eastern United States
Geography of the Interior United States
Geography of the Western United States
Historic regions of the United States
List of islands of the United States
List of mountains of the United States
List of North American deserts
List of US government designations for places
Mountain peaks of the United States
Public Land Survey System
Regions of the United States
Territorial evolution of the United States
Russia-United States maritime boundary
* [http://tapestry.usgs.gov USGS: Tapestry of Time and Terrain]
* [http://www.usgs.gov/ United States Geological Survey] - Maintains free aerial maps
* [http://www.nationalatlas.gov/ National Atlas of the United States of America]
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