Geography of the United States


The term "United States," when used in the geographic sense, refers to the contiguous United States, Alaska, Hawaii, the five insular territories of Puerto Rico, Northern Mariana Islands, U.S. Virgin Islands, Guam, American Samoa, and minor outlying possessions. The United States shares land borders with Canada and Mexico and maritime borders with Russia, Cuba, the Bahamas, and many other countries, mainly in the Caribbean, in addition to Canada and Mexico. The northern border of the United States with Canada is the world's longest bi-national land border.
The state of Hawaii is physiographically and ethnologically part of the Polynesian subregion of Oceania. U.S. territories are located in the Pacific Ocean and the Caribbean.

Area

From 1989 through 1996, the total area of the US was listed as . The listed total area changed to in 1997, to in 2004, to in 2006, and to in 2007. Currently, the CIA World Factbook gives, the United Nations Statistics Division gives, and the Encyclopedia Britannica gives . These sources consider only the 50 states and the Federal District and exclude overseas territories. The US has the 2nd largest Exclusive Economic Zone of .
By total area, 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. Both countries are smaller than Russia and Canada in total area but are larger than Brazil. By land area only, the United States is the world's third largest country, after Russia and China, with Canada in fourth. Whether the US or China is the third largest country by total area depends on two factors: the validity of China's claim on Aksai Chin and Trans-Karakoram Tract ; and how the US calculates its surface area. Since the initial publishing of the World Factbook, the CIA has updated the total area of the United States several times.

General characteristics

The United States shares land borders with Canada to the north and Mexico to the south, a territorial water border with Russia in the northwest, and two territorial water borders in the southeast between Florida and Cuba, and Florida and the Bahamas. The contiguous 48 states are otherwise bounded by the Pacific Ocean on the west, the Atlantic Ocean on the east, and the Gulf of Mexico to the southeast. Alaska borders the Pacific Ocean to the south and southwest, the Bering Strait to the west, and the Arctic Ocean to the north; Hawaii lies 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 contiguous United States, and as the "Lower 48". Alaska, which is included in the term "continental United States", is located at the northwestern end of North America.
The nation's capital city, Washington, D.C., was established in 1800 after being relocated there from Philadelphia. It was established as a federal district located on land donated by the state of Maryland; Virginia also donated land, but it was returned in 1849. The United States also has overseas territories with varying levels of autonomy and organization, including the Caribbean territories of Puerto Rico and the U.S. Virgin Islands, formerly known as the Danish Virgin Islands and purchased by the United States at the beginning of World War II, the Pacific territories of American Samoa, Guam and the Northern Mariana Islands, and several uninhabited island territories. Some of the territories acquired were part of the territorial evolution of the United States or a product of the nation's effort to gain access to the east.
Nearly all of the United States is in the Northern Hemisphere with the exception of American Samoa and Jarvis Island.

Physiographic divisions

Within the continental U.S. there are eight distinct physiographic divisions. These major divisions are:
File:MountMcKinley BA.jpg|thumb|Denali, federally designated as Mount McKinley, in Alaska, is the tallest mountain in North America, at.
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. This broad coastal plain and barrier islands make up the widest and longest beaches in the United States, much of it composed of soft, white sands. The Florida Keys are a string of coral islands that reach the southernmost city on the United States mainland at Key West in South Florida.
Areas further inland feature rolling hills, mountains, and a diverse collection of temperate and subtropical moist and wet forests. Parts of interior Florida and South Carolina are also home to sandhill communities. The Appalachian Mountains form a line of low mountains separating the eastern seaboard from the Great Lakes and the Mississippi basins. New England features rocky seacoasts and rugged mountains with peaks up to 6,200 feet and valleys dotted with rivers and streams. Offshore islands dot the Atlantic and Gulf coasts. A recent global remote sensing analysis suggested that there were 6,622 km2 of tidal flats in the United States, making it the 4th ranked country in terms of tidal flat area.
The five Great Lakes are located in the north-central portion of the country, four of them forming part of the border with Canada; only Lake Michigan is situated entirely within the United States. The southeast United States, generally stretching from the Ohio River southwards, includes a variety of warm temperate and subtropical moist and wet forests, as well as warm temperate and subtropical dry forests nearer the Great Plains in the west of the region. West of the Appalachians lies the lush Mississippi River basin and two large eastern tributaries, the Ohio River and the Tennessee River. The Ohio and Tennessee valleys and the Midwest consist largely of rolling hills, interior highlands and small mountains, jungle-like marsh and swampland near the Ohio River, and productive farmland, stretching south to the Gulf Coast. The Midwest also has a vast amount of cave systems.
The Great Plains lie 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 prairie in 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 Mountains and the Appalachian Mountains.
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 Canada and stretching nearly to Mexico. The Rocky Mountain region is the highest region of the United States by average elevation. The Rocky Mountains generally contain fairly mild slopes and wider peaks compared to some of the other great mountain ranges, with a few exceptions, including the Teton Range in Wyoming and the Sawatch Range in Colorado. The highest peaks of the Rockies are found in Colorado, the tallest peak being Mount Elbert at. Instead of being one generally continuous and solid mountain range, it is broken up into several 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 Corners region, is considered to have some of the most spectacular scenery in the world. It is accentuated in such national parks as Grand Canyon, Arches, Mesa Verde and Bryce Canyon, among others. Other smaller Intermontane areas include the Columbia Plateau, which covers eastern Washington state, western Idaho and northeast Oregon and the Snake River Plain in southern Idaho.
The Intermontane Plateaus come to an end at the Cascade Range and the Sierra Nevada. The Cascades consist of largely intermittent, volcanic mountains, many 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. It is located at the boundary between California's Inyo and Tulare counties, just west-northwest of the lowest point in North America at the Badwater Basin in Death Valley National Park at below sea level. 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 California and the Willamette Valley in Oregon. Along the coast is a series of low mountain ranges known as the Pacific Coast Ranges.
Alaska contains some of the most dramatic 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 Alaska in the Pacific Ocean, is a chain of tropical, volcanic islands, popular as a tourist destination for many from East Asia and the mainland United States.
The territories of Puerto Rico and the U.S. Virgin Islands encompass a number of tropical isles in the northeastern Caribbean Sea. In the Pacific Ocean the territories of Guam and the Northern Mariana Islands occupy the limestone and volcanic isles of the Mariana archipelago, and American Samoa encompasses volcanic peaks and coral atolls in the eastern part of the Samoan Islands chain.
The Atlantic coast of the United States is low, with minor exceptions. The Appalachian Highland owes its oblique northeast–southwest trend to crustal deformations which in very early geological time gave a beginning to what later came to be the Appalachian Mountain system. This system had its climax of deformation so long ago 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.
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 mountain systems lie the Intermontane Plateaus. Both the Columbia River and Colorado River rise far inland near the easternmost members of the Cordilleran system, and flow through plateaus and intermontane basins to the ocean. Heavy forests cover the northwest coast, but elsewhere trees are found only on the higher ranges below the Alpine region. The intermontane valleys, plateaus and basins range from treeless to desert with the most arid region being in the southwest.
Elevation extremes: