Mesa Verde

A great concentration of ancestral Pueblo Indian dwellings, built from the 6th to the 12th century, can be found on the Mesa Verde plateau in south-west Colorado at an altitude of more than 2,600 m. Some 4,400 sites have been recorded, including villages built on the Mesa top. There are also imposing cliff dwellings, built of stone and comprising more than 100 rooms.

Yellowstone

The vast natural forest of Yellowstone National Park covers nearly 9,000 km² ; 96% of the park lies in Wyoming, 3% in Montana and 1% in Idaho. Yellowstone contains half of all the world's known geothermal features, with more than 10,000 examples. It also has the world's largest concentration of geysers (more than 300 geyers, or two thirds of all those on the planet). Established in 1872, Yellowstone is equally known for its wildlife, such as grizzly bears, wolves, bison and wapitis.