The continental territory can be divided into four main morphological zones, elongated in the direction of the meridians; from the Pacific to the Atlantic one first encounters a region of high reliefs; to East of these, there are large flat expanses drained by the Mississippi – Missouri system ; further to East another mountainous area, older, and finally a coastal selvedge along the Atlantic.
● The Atlantic coast is generally low, not very extensive, articulated only by river estuaries (Hudson, on which New York stands ; Potomac, with the capital Washington; more in S Savannah, with the city of the same name) and from the peninsula of Capo Cod. AS, between the Atlantic and the Gulf of Mexico, the lower peninsula of Florida extends for over 500 km, affected by vast swampy areas (everglades).
● Behind the coastal plain, a false plain about a hundred kilometers wide (piedmont belt) first gradually rises, up to about 600 m, and then abruptly up to the first of the ridges that form the Appalachian Mountains, stretched for about 2500 km towards the SW- NEITHER. Erosion has softened all forms and the highest ridge is that of the Blue Ridge, where Mount Mitchell barely exceeds 2000m. Beyond the watershed, erosion has filled most of the valleys, forming the Cumberland Plateau. The great rivers that flow to the West (Ohio, Kentucky, Tennessee) flow into the Mississippi, with the exception of a few that make their way to the Gulf of Mexico, such as Alabama. Towards the north, a series of moraine hills embrace the region of the Great Lakes, of glacial excavation, crossed by the border between the USA and Canada in the direction of its length. Just W of the Great Lakes the Mississippi is born, which in practice lacks a real high course: its sources are at about 450 m of altitude, in a few kilometers it drops to 300 m and to reach the mouth it still runs almost 4000 km. Its left tributaries are the Appalachian rivers; more relevant are those on the right, which arise from the Rocky Mountains and run through the Great Plains (Great Plains) and the prairies (prairies). The largest is Missouri which, from the headwaters of the highest branch (the Red Rock) to the confluence in the Mississippi, is more than twice as long as the approximately 2000 km traveled there by the Mississippi itself, considered however the main course, given the distinct flow higher and more regular regimen. After the confluence of the Missouri, the Mississippi course is approximately 1km wide, after the confluence of the Ohio it exceeds 2km, and after the confluence of Arkansas and Red River, reaches to exceed 3 km. The Mississippi receives a significant solid load from its tributaries, with which it builds a continuously advancing delta at its mouth. The accumulation of debris has also raised the entire lower course, making the river suspended, which causes frequent very large floods. AO of the mouth of the Mississippi flows into the Río Grande which, with the tributary Pecos, collects the waters of the southern sector of the Rocky Mountains.
● The Great Plains region is a slightly sloping false plain, rising from the right of the Mississippi up to around 600m, to the western relief region. These, like the Alaska reliefs to which they are structurally connected, are made up of ancient formations, however involved in the Meso-Cenozoic uprisings. It is an articulated system of ridges and reliefs, where many peaks exceed 4200 m, in Wyoming as well as in Colorado, Utah and New Mexico. In the northern part there was volcanic activity, which produced lava expansions, and still feeds notable phenomena of secondary volcanism, so much so that the first national park in the world, Yellowstone, was established there (1872). In the southernmost part it exceeds 4300 m in the Sawatch Range and in the Sangre de Cristo Mountains. AO the reliefs decline towards a vast region with an average height of 1000-1500 m, which the Wasatch Mountains divide into the Great Basin to the NW and the Colorado Plateau to the SE. The whole area is arid and partly endorheic; maximum internal basin is that of the Great Salt Lake, at the north-western slopes of the Wasatches. The largest river in the Great Basin is the Snake, which opens its way through deep canyons until it flows into the river Columbia, from Canada. The Colorado Plateau has a tabular structure, for the most part made up of Paleozoic sandstones, in which the Colorado River has carved out the impressive Grand Canyon, which in some places deepens for 1800 m, until it reveals old rocks. Precambrian. AO the highland region is bounded by the Cascade Range and the Sierra Nevada, and along the coast by the Coastal Range. The highest peaks (Whitney, Rainier, Shasta, over 4000m) are volcanic systems. AN, in the Cascade Range, the Columbia River opens its way to the Pacific, while San Joaquin further south and the Sacramento join a short distance from the coast, flowing into the San Francisco Bay. The aridity of the plateaus is accentuated towards the West, where there are extensive desert areas, which also drop below sea level in the well-known Valley of Death, in California, where it reaches −84 m, and in the endorheic basin of the Salton Sea, at −75 m. All the reliefs near the Pacific are recent and show strong seismicity. Volcanism is also active.