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Geography of the United States

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Forty-nine states in the United States (all except Hawaii) lie on the North American continent; 48 of these (all except Alaska and Hawaii) are contiguous and form the continental United States.

Geography of the United States
Topography of the 48 states of the U.S. mainland
Topography of the 48 states of the U.S. mainland
Area
Total 9,629,091 km²

3,717,813 sq. mi

Land 9,158,960 km²

3,536,294 sq. mi

Water 470,131 km²

181,519 sq. mi

Latitude 38°0' N
Longitude 97°0'W
Borders
Canada 8,893 km

5,526 miles

Mexico 3,326 km

2,067 miles

Coastlines 19,924 km

12,380 miles

Maritime claims
Contiguous zone 24 nautical miles (44 km)
Economic zone 200 nautical miles (370 km)
Territorial sea 12 nautical miles (22 km)

The United States shares land borders with Canada and Mexico, and water borders with Russia and the Bahamas.

The western half of the northern boundary is exactly at 49° N (apart from Alaska being more north and Vancouver Island, Canada reaching more south). At the eastern half the northern boundary is more south, except for Lake of the Woods, the most northerly part of the U.S. apart from Alaska.

Area

The U.S. is the world's third or fourth (disputed) largest country (by total area) after Russia, Canada, and perhaps China with an area roughly:

Physical geography

 
A satellite composite image of the contiguous United States. Deciduous vegetation and grasslands prevail in the east, transitioning to prairies, boreal forests, and the Rockies in the west, and deserts in the southwest. In the northeast, the coasts of the Great Lakes and Atlantic seaboard host much of the country's population.

The United States shares land borders with Canada (to the north) and Mexico (to the south), and territorial water boundaries with Canada, Russia, the Bahamas, and numerous smaller nations. It is 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, the Bering Strait to the west, and the Arctic Ocean to the north, while 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 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 Hawaii is an archipelago in the Pacific Ocean. The capital city, Washington, District of Columbia, is a federal district located on land donated by the state of Maryland. (Virginia had also donated land, but it was returned in 1847.) The United States also has overseas territories with varying levels of independence and organization.

In total area (including inland water), Russia and 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.

 
Mount McKinley, Alaska, the highest point in North America at 20,320 ft (6,194 m)

The eastern United States consists largely of rolling hills and temperate forests. The Appalachian Mountains form a line of low mountains separating the eastern seaboard from the Great Lakes and Mississippi Basin. The five Great Lakes are located in the north-central portion of the country, four of them forming part of the border with Canada. The southeast contains subtropical forests and, near the coast, mangrove wetlands, especially in Florida. West of the Appalachians lies the Mississippi River basin and two largest eastern tributaries, the Ohio River and Tennessee River. The Ohio and Tennessee Valleys and the Midwest consist largely of rolling hills and productive farmland, stretching south to the Gulf Coast.

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 extensive grasslands, from tallgrass prairie in the east to shortgrass steppe in the western High Plains. Elevation rises gradually from less than a few hundred feet 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, a region known as The Ozarks.

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 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 Mountains in Wyoming and the Sawatch Range in 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 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, and Bryce Canyon, among others.

 
The Grand Canyon from Moran Point. The Grand Canyon is among the most famous locations in the country.

The Intermontane Plateaus come to an end at the Cascade Range and 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 California and the Willamette Valley in Oregon. Along the coast is a series of low mountain ranges known as the Pacific Coast Ranges. Much of the Pacific Northwest coast is inhabited by some of the densest vegetation outside of the Tropics, and also the tallest trees in the world (the Redwoods).

Alaska contains 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 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 geography of the United States varies across its immense area. Within the contential U.S., eight distinct physiographic divisions exist, though each is composed of several smaller physiographic subdivisions. These major divisions are the:

 
Delicate Arch, Arches National Park, Utah

The Atlantic coast of the United States is, with minor exceptions, low. Here, lie the Atlantic Plain and Appalachian Highlands. 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 (probably in Permian 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 below, known as a physiographical map, shows geographical and topographical information 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 subarticles found in the additional topics subsection below.

 
Physiographic Regions of the United States.

While the east 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 intermontane valleys, plateaus and basins range from treeless to desert with the very arid region being in the southwest.

Both the Columbia River and Colorado River rise 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 Mexico northward, 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.

See also: List of North American deserts

 
The Strip, Las Vegas, Nevada

Elevation extremes:

Cultural regions

The continental U.S. is often subdivided into six major cultural regions which not so coincidentally often share common natural features and terrain as well as similar ethnic groups. Those regions are:

  • New England - One of the regions first settled by European immigrants, this region lies in the upper north-east of the U.S. geographically. New England is dominated by rocky uplands and sandy outwash plains and with a climate having stark seasonal changes.
  • Mid-Atlantic - Another region settled earlier on in the U.S. history and home to the capital of the United States, Washington, D.C. Its geography is varied, including forested ridges and marshy lowlands.
  • South - Culturally perhaps the most different of the states, the South still maintains an identity developed prior to and during the Civil War. The South consists mostly of low coastal areas drained by comparatively few rivers. There is a wide band of piedmont soil, mostly thick clay, and forbidding mountain mazes.
  • Midwest - This region was settled during the late 1700s and early 1800s well after the east coast. Many of these states lie on the Great Plains.
  • Southwest - The Southwest has a drier climate than the Midwest. The population is less dense and, with strong Spanish-American and Native American components, more ethnically varied than neighboring areas. Outside the cities, the region is a land of open spaces, much of which is desert. The magnificent Grand Canyon is located in this region, as is Monument Valley.
  • Western states - The west is home to the pacific coast of the United States as well as many gorges, plateaus and mountain ranges, the most famous being the Rocky Mountains.

For more information on other "cultural" regions of the U.S., see List of regions of the United States.

Climate

 
Average precipitation

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 Hawaii and southern Florida, polar in Alaska, semiarid in the Great Plains west of the 100th meridian, Mediterranean in coastal California and 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.

 
Deep snow during the Blizzard of 2006 Nor'easter in Brooklyn, New York City.

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 Mountains pick 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 Mexico is 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 Plains also 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.

 
The U.S. State of Hawaii has a year-round tropical climate, and is known for its many beaches, such as this one on O'ahu.

The Great Basin and 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 monsoon from the Gulf of California from July-September, which brings localized but often severe thunderstorms to the region.

Much of California consists of a Mediterranean climate, with sometimes excessive rainfall from October-April and nearly no rain the rest of the year. In the Pacific Northwest rain 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 snow that falls south and east of the Great Lakes, especially in the hilly portions of the Upper Peninsula of Michigan and on the Tug Hill Plateau in New York. The Wasatch Front and Wasatch Range in Utah can also receive significant lake effect accumulations off of the Great Salt Lake.

Natural disasters

 
Hurricanes are among the most devastating natural disasters that impact the United States. This picture shows the Coast Guard assisting in relief during Hurricane Katrina in 2005.

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 Plains have developed.[1] 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 experiences, 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 Texas north to Kansas and east into Tennessee is 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 Coast as well as Hawaii in the Pacific Ocean. Particularly at risk are the central and southern Texas coasts, the area from southeastern Louisiana east to the Florida Panhandle, the east coast of Florida, and the Outer Banks of 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 Andrew in 1992, and Hurricane Katrina in 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 monsoon season 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 Peninsula and 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, Oregon and northern California along 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. Helens in Washington.

The Ring of Fire makes California and southern Alaska particularly vulnerable to earthquakes. Earthquakes can cause extensive damage, such as the 1906 San Francisco Earthquake or the 1964 Good Friday Earthquake near Anchorage, Alaska. California is well known for seismic activity, and requires large structures to be earthquake proofed to minimize loss of life and property. Outside of devastating earthquakes, California experiences minor earthquakes on a regular basis.

Natural resources

Natural resources: coal, copper, lead, molybdenum, phosphates, uranium, bauxite, gold, iron, mercury, nickel, potash, silver, tungsten, zinc, petroleum, natural gas, timber

Land use: arable land: 19% permanent crops: 0% permanent pastures: 25% forests and woodland: 30% other: 26% (1993 est.)

Irrigated land: 79,900 square miles (207,000 km²) (1993 est.)
Natural hazards: tsunamis, volcanoes, and earthquake activity around Pacific Basin; hurricanes along the Atlantic and Gulf of Mexico coasts; tornadoes in the midwest and southeast; mud slides in California; forest fires in the west; flooding; permafrost in northern Alaska, a major impediment to development

Environment

Environment - current issues: air pollution resulting in acid rain in both the US and Canada; the US is the largest single emitter of carbon dioxide from the burning of fossil fuels; water pollution from runoff of pesticides and fertilizers; very limited natural fresh water resources in much of the western part of the country require careful management; desertification

Environment - international agreements: party to: Air Pollution, Air Pollution-Nitrogen Oxides, Antarctic-Environmental Protocol, Antarctic Treaty, Climate Change, Endangered Species, Environmental Modification, Marine Dumping, Marine Life Conservation, Nuclear Test Ban, Ozone Layer Protection, Ship Pollution, Tropical Timber 83, Tropical Timber 94, Wetlands, Whaling signed, but not ratified: Air Pollution-Persistent Organic Pollutants, Air Pollution-Volatile Organic Compounds, Biodiversity, Climate Change-Kyoto Protocol, Desertification, Hazardous Wastes

Public lands

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:

See also

Template:US topics

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