Geography |
The United States of America consists of 48 contiguous states in North America and the non-contiguous states of Alaska in the north-west corner of North America and Hawaii in the Pacific Ocean. The conterminous 48 states are bounded on the north by Canada, on the east by the Atlantic Ocean, on the south by the Gulf of Mexico and Mexico, and on the west by the Pacific Ocean. The total area is 9 809 630 km2.
From northern Maine the Appalachian Mountains extend south-westward to northern Alabama. Although the Appalachians are fairly low (mostly below 2 000 m), they are rugged with many parallel ranges and valleys. Some of the individual mountain ranges include the White Mountains and the Green Mountains in northern New England, the Adirondack Uplands of northern New York and the Blue Ridge Mountains.
Coastal lowlands extend down the east coast from south-eastern Maine to Florida and across the southern United States to eastern Texas. In the east, they can be broken into two divisions, the hilly Piedmont and the Atlantic Coastal Plain. The Gulf Coastal Plain borders the Gulf of Mexico from Florida to southern Texas. The plains are generally flat.
From the Appalachian Highlands in the east to the Rocky Mountains in the west lie the interior plains. Glaciers covered much of the northern portion of this region during the Ice Age. The plains slope gradually upward from east to west and get progressively drier. The western part of the region, called the Great Plains, has vast grasslands and fertile soils suitable for dry-land farming. Some areas of rugged hills, such as the Black Hills of South Dakota and Wyoming and the Ozark-Ouachita Highlands of southern Missouri, north-west Arkansas, and eastern Oklahoma, rise up out of the plains. Along the northern border with Canada lie the five Great Lakes, the largest group of freshwater lakes in the world. The Mississippi River, together with its major tributaries, the Missouri and Ohio, are the major rivers of the interior plains.
Much of the western United States is a land of high mountain ranges divided by high plateaus and deep valleys. The Rocky Mountains extend from Canada to Mexico, with many peaks over 3 000 m. Between the Rocky Mountains and the Cascade and Sierra Nevada ranges lies a series of arid basins separated by low mountain ranges. The Colorado river in the south-west and the Columbia River in the north-west, with their tributaries, and the major rivers draining the interior west. A series of low mountains borders much of the west coast, and fertile valleys lie between them and the parallel Cascade and Sierra Nevada ranges.
Alaska's south-east coast is a spectacular series of islands and fjords with glacier-filled valleys, rising to permanent icefields above. Southern Alaska is mountainous, cumulating in the highest peak in North America, Mt. Denali (6 184 m). The centre of the state is a huge basin drained mainly by the Yukon river, rising to the Brooks Range in the north. A low coastal plain faces the Arctic Ocean.
The Hawaiian islands are of volcanic origin, lying in a north-west to south-east line. The islands to the north-west are the oldest, with deeper soils and more dissected topography. Volcanic action is still taking place on the youngest island, Hawaii.
Given the wide range of elevation, topography, and latitude, the climate of the United States is extremely varied. Average annual temperatures range from -13° C in Barrow, Alaska, to 25.7° C in Death Valley, California. The highest temperature ever recorded in the country was 57° C at Death Valley. The lowest recorded temperature was -62° C near Barrow. Precipitation varies from a yearly average of less than 50 mm at Death Valley to about 1 170 mm at Mount Waialeale in Hawaii. In general, however, much of the United States has a moderate temperate climate.
The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.