United States Geography, Climate & Nature

The contiguous United States spans a continent's worth of terrain -- the Appalachian Mountains running along the east, the vast Great Plains at its center, the Rocky Mountains dividing the interior from the Pacific coast, and desert basins across much of the American Southwest.

The Mississippi River, the country's longest, drains most of the interior and has historically shaped settlement and trade. The Great Lakes, shared with Canada, sit along the northern border, anchoring the historically industrial cities of the Midwest.

The West is defined by dramatic elevation change -- the Grand Canyon, Yosemite's granite cliffs, and Death Valley, the lowest and hottest point in North America, all within a few hundred kilometers of each other.

The country's size and range of latitudes give it nearly every climate type found anywhere in the world. The Northeast and Midwest have a four-season continental climate, while the Southeast is humid subtropical, with mild winters and hot, storm-prone summers.

The American Southwest is a true desert climate -- summers routinely exceed 40°C (104°F) -- while the Pacific Northwest is famously wet and mild, and California's coast enjoys a Mediterranean climate.

Alaska ranges from subarctic to true Arctic conditions, while Hawaii's tropical climate stays warm year-round. Hurricane season (June-November) affects the Gulf and Atlantic coasts, and tornado season (spring) affects the central "Tornado Alley" states.

The United States spans more latitude and more climate than almost any single country, and its biology follows: Arctic tundra in Alaska, temperate rainforest on the Pacific Northwest coast, desert in the American Southwest, subtropical wetland in Florida, and the largest temperate grassland system on earth through the middle. Its native flora alone runs to about 17,000 species of vascular plants, with tens of thousands more algae, lichens, fungi and mosses, and another 3,800 non-native vascular species now established outside cultivation.

Two features shape what a visitor can actually see. The first is that the great biological divisions run north to south -- the Rockies, the Appalachians, the Mississippi corridor -- so a drive across the country crosses more ecological boundaries than a drive down it. The second is public ownership: vast contiguous blocks of land are held federally, which is why intact habitat survives at a scale that a country this developed would not otherwise have, and why so much of it is reachable on a made road.

The pressure is real all the same. A substantial share of US vascular plants are considered rare, threatened or endangered either rangewide or within particular states, and the losses are concentrated where habitat is fragmented rather than where it is remote.

An estimated 432 mammal species live in the continental United States, alongside 311 known reptiles, 295 amphibians, 1,154 fish and more than 100,000 known insect species. What distinguishes American wildlife for a visitor is less the count than the accessibility: large mammals are genuinely visible from public roads and short trails in a way that is unusual for a wealthy, populous country.

The bison is the animal that carries the country's conservation history in one figure. An estimated 30 to 60 million once roamed the plains, forming the largest concentration of large mammals on earth, before nineteenth-century hunting reduced the population to fewer than 1,000 individuals by 1889. It was recognised by Congress as the national mammal in 2016 through the National Bison Legacy Act, and the herds a visitor now sees in Yellowstone and on the plains refuges are descended from that remnant.

Beyond it, the animals most visitors hope for are concentrated in the west and the north: grizzly and black bear, elk, moose, pronghorn, bighorn sheep and wolves in the northern Rockies; alligators and wading birds in the southern wetlands; whales along both coasts. The practical point is seasonal rather than geographic -- most large mammals are active at dawn and dusk, and the middle of a summer day in a famous park is the worst time to look for any of them.