Geography of the United States

As the third-largest country by size, the United States has a varied geography, including woodlands, rainforests, mountains, grassy plains, rocky seacoasts, arid deserts, and volcanic islands. Within its borders lie both the highest and lowest points in North America, some of the youngest mountains on Earth, one of the world’s longest river systems, and the planet’s largest coal reserves. The total area of the country is 3,794,079 square miles (9,826,675 square kilometers).

The climate is mostly temperate but similarly varied, with temperatures typically cooler in the north. The major climate groups are dry, continental, polar, temperate, and tropical. The hottest state on average is Florida at 70.7 degrees Fahrenheit (21.5 degrees Celsius), while Alaska is the coldest at 26.6 degrees F (-3 degrees C). Hawaii averages the most annual precipitation (63.7 inches/1,618 millimeters), while Nevada sees the least (9.5 inches/241 millimeters).

Background

The United States is a part of the North American continent, which also includes Canada, Mexico, the Caribbean, Greenland, and numerous other countries. Two hundred million years ago, North America was part of the Pangaea supercontinent. As the tectonic plates of Earth’s crust gradually moved, separating the continents, the floor of the vast Panthalassa Ocean was subducted under North America as the continent moved westward. North America collided with an island chain about 150 million years ago, with the resulting upheaval creating the Rocky Mountains. A complicated series of collisions and subductions caused a wide range of terrain types to develop along the western edge of the continent. Mountains in the east began to form about 750 million years ago, when the continental crust expanded, and the supercontinent started to pull apart. More than 200 million years later, the continental crust broke apart, with the pieces drifting away from each other. Gradually, the low areas between plates filled with seawater and sediments. About 270 million years ago, the North American and African continents collided, with the plates pushing westward, crumpling, and forming mountains.

North America, Earth’s third-largest continent, ranges from the Aleutian Islands in the northwest, the Arctic Ocean in the north, Greenland in the northeast, the Isthmus of Panama in the south, the Pacific Ocean to the west, and the Caribbean Sea and North Atlantic islands in the east.

The highest point on the continent at 20,310 feet (6,190 meters) above sea level is Denali, formerly Mount McKinley, in the state of Alaska. Death Valley in California is the lowest point in North America, at 282 feet (86 meters) below sea level. The coastline, which is second only to Asia in length, is 37,000 miles (60,000 kilometers) and highly irregular.

Overview

The United States contains three major physical regions—the western mountains, the Great Plains, and the varied eastern region—that include most of the major types of biomes. The major feature of the West is the Rocky Mountain range, the largest on the continent, which extends northward into Canada. The Great Plains, which likewise extend into Canada, are an expanse of rich grassland. Major features of the East are the Appalachian Mountains and the Atlantic coastal plain. These physical regions overlap to varying degrees with the nine climate regions of the contiguous United States.

The Western Region

The Rocky Mountains, one of the parallel ranges known as the Cordilleras, are considerably younger than the ranges in the east. Other mountains in the West are the Cascades, which run from British Columbia to Northern California, and the Sierra Nevada range in California. Some of the mountains in the Cascades are among Earth’s youngest, having begun to form about one million years ago.

The mountains of the west have a tremendous impact on weather and climate. The ranges block a great deal of rainfall on their eastern sides. The Mojave and Great Basin Deserts, as well as the Sonoran and Chihuahua Deserts, parts of which are in the United States, all lie in mountains’ rain shadows. The Sonoran Desert is in the Coast Ranges’ rain shadow, while the Mojave and Chihuahua Deserts are in the rain shadows of the Sierra Nevada and Sierra Madre, respectively. These biomes are home to desert plants, including the saguaro cactus and mesquite, and animals, including the Gila monster, rattlesnake, and roadrunner.

The northwest coast of North America, from Alaska to southern California, is rimmed with temperate rainforest. In the US Pacific Northwest, this coniferous forest grows in a band about 35 miles (56 kilometers) wide. This area has a regional maritime climate that does not see long stretches of temperature extremes but sees precipitation all year. The major types of forest along the Pacific Coast are boreal rainforest, which grows near alpine glaciers in Alaska and Canada; humid temperate rainforest, which receives more than 100 inches (254 centimeters) of precipitation annually; seasonal temperate rainforest, which is found in Oregon and Washington and receives from 78 to 160 inches (198 to 406 centimeters) of precipitation, mostly in autumn and winter; and warm temperate rainforest, which stretches from the California-Oregon border to south of San Francisco Bay and is known for dry summers, annual precipitation greater than 125 inches (317 centimeters), and coastal redwoods. These iconic trees were once plentiful, but in modern times, only about 4 percent of the original forest remains, primarily in isolated stands on protected lands.

The weather and climate in the West vary considerably. The Northwest climate region, which consists of Idaho, Oregon, and Washington, is typically cooler and wetter than the Western climate regions of California and Nevada and the Southwest region, which includes Arizona, Colorado, New Mexico, and Utah. Temperate rainforests in the mountains receive between 100 and 200 inches (254 to 508 centimeters) of precipitation annually. Species native to these rainforests include the Douglas fir, Sitka spruce, and western red cedar; indigenous animal species include black bears, marmots, and the Roosevelt elk.

The Great Plains

The Great Plains region in the center of the United States includes grasslands in all or parts of Colorado, Iowa, Kansas, Minnesota, Missouri, Montana, Nebraska, New Mexico, North Dakota, Oklahoma, South Dakota, Texas, and Wyoming. This region has traditionally been called the continent’s breadbasket because of the importance of the grain grown here for domestic use and export. The fertility of the soil is due to the organic matter deposited during the last ice age, which began about thirty thousand years ago and ended about twelve thousand years ago. As glaciers melted, the water deposited sediment across the plains, laying down layers of rich soil.

Few large plants grow on the prairies because of the weather, but native grasses are well adapted. The region does boast some prairie woodlands, shrublands, and forests. The grasslands make up North America’s largest biome. Habitats include shortgrass prairies, home to native grasses that grow to 10 inches (25 centimeters), and tallgrass prairies, where grasses up to 7 feet (2 meters) tall wave. These plants provide food and shelter to a range of creatures, including bison and prairie dogs. Multiple introduced species, such as crested wheatgrass and Kentucky bluegrass, compete with and crowd out many native species.

The Northern Rockies and Plains climate region includes Montana, Nebraska, North Dakota, South Dakota, and Wyoming, while the Southern climate region includes Arkansas, Kansas, Louisiana, Mississippi, Oklahoma, and Texas. The Great Plains see blizzards, cold waves, droughts, floods, heat waves, and severe weather.

The Eastern Region

This area includes the Appalachian Mountain Range and the Atlantic coastal plain. Much of the east consists of hills and low mountains. Deposits of coal and other minerals have been mined from these mountains for centuries. The mountains here are older than those in the west. For example, the base rocks of the Appalachians are more than one billion years old. Over many millions of years, these mountains have eroded. Sediment from the rocks washed down to the coastal plains, forming rich soils.

Marsh, river, and wetland areas of the Atlantic coastal plain stretch from the mountains eastward. Wetlands, areas where soil is permanently or seasonally saturated, are a major biome in the east. Among the most well-known wetland systems are the Florida Everglades. At more than 4,300 square miles (11,137 square kilometers), it is the country’s largest wetland system. Major river systems in the Eastern United States include the Delaware, Mississippi, Potomac, Savannah, and Susquehanna. These river habitats have a high richness and variety of species, including aquatic insects, fish, and mollusks, as well as alligators and giant aquatic salamanders. While long ago bottomlands flooded for months of the year, humans have constructed channels and levees to restrict flooding. Acid mine drainage, sedimentation, and urban runoff are some of the modern threats to riparian habitats. The eastern geographical region's climate is generally humid continental in the north and humid subtropical in the south.

Alaska and Hawaii

The two states not part of the contiguous United States have vastly different landscapes, weather, biomes, and inhabitants. The climate of Hawaii is tropical, while that of Alaska is both arctic and temperate. Both have volcanic activity.

Alaska has more than three million lakes and three thousand rivers. The Yukon, which flows through the state and northwest Canada, is the third-longest North American river. Alaska is the largest state at 586,412 square miles (1.5 million square kilometers) but has a low population density. It has 33,904 miles (54,563 kilometers) of shoreline and shares a 1,538-mile (2,475-kilometer)-long border with Canada. Alaska has 1,800 named islands. About 5 percent of the state is covered by ice fields. The Bering Glacier, more than 122 miles (196 kilometers) long, is the largest glacier in North America and the longest of the state’s multiple glaciers. Major land features include the Alaska Range, the Aleutian Islands, the Brooks Mountain Range, the Panhandle Archipelago in the southeast, and the treeless tundra.

Hawaii’s land features include fern and bamboo forests, lava deserts, ocean cliffs, and tropical coastal areas. Mauna Kea is frequently capped with snow. Most of the islands in this archipelago have both cliffs and coastal plains. Seven of the eight main islands are inhabited. The largest and youngest island, Hawaii, is growing as lava continues to flow from Kilauea, one of the island’s five volcanoes. The others are Hualalai, Kohala, Mauna Kea, and Mauna Loa. The western side of the island is a rain shadow. The state’s mild, tropical climate is a major tourist draw.

Inhabitants

The 2020 US Census recorded the nation’s population at 331,449,281. Those identifying as White alone, not Hispanic or Latino, made up 58.9 percent, while Black alone accounted for 13.6 percent, Hispanic or Latino 19.1 percent, Asian alone 6.3 percent, American Indian and Alaska Native alone 1.3 percent, and Native Hawaiian and other Pacific Islanders alone 0.3 percent. Those

The population density of the United States in 2023 was 96 people per square mile, or 37 people per square kilometer. The greatest concentrations of people were on the coasts. According to the US Census, 38.6 percent of the population lived in the South, 23.6 percent lived in the West, 20.6 percent were residents of the Midwest, and 17.1 percent called the Northeast home. Alaska had the lowest population density at 1.28 per square mile. The population density of the District of Columbia was 11,685.81 people per square mile, significantly more than the densest state, which was New Jersey with 1,207.83 per square mile. The largest urban area in North America is the New York City metropolitan area, which is home to more than 23.7 million people.

Land Use

Humans have altered the physical environment for thousands of years. Early changes included clearing land for agriculture and damming waterways to store water or change their course. Later alterations occurred as humans felled forests for timber, dug mines, and cleared obstacles to transportation. The nineteenth century saw engineers solving problems that stood in the way of railroads crisscrossing the continent. In the mid-twentieth century, the government embarked on the construction of an extensive highway system. These projects include building bridges and blasting through rock to create smooth roads and tunnels. While deep mining in many areas has ceased or slowed, in some states, mining companies use explosives to remove the tops of mountains and expose veins of coal. Some groups have succeeded in having dams, which often impede wildlife such as migrating salmon, removed from rivers. Newer dams have been designed to lessen their impact on wildlife.

About 52 percent of land in the United States is used for agricultural production. The largest portion of land is devoted to grassland pasture and range uses, according to the Economic Research Service’s 2012 Major Land Uses (MLU) report. Other uses are forest (including grazed forest land) and cropland. Land area in the top three categories—grassland, forest, and cropland—has remained stable for decades, though the proportions of these categories fluctuate. However, agricultural productivity has increased substantially because of advances in disease and insect control, better crop varieties, and new technology. Crop preferences have also changed. For example, demand for corn for biofuel and soybeans for export has increased, while wheat acreage has declined by 52 percent since the early 1980s. Since the MLU report began in 1945, land for special uses, including state and national parks and wilderness areas, has increased a great deal.

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