The Grand Canyon in Arizona is a steep-sided canyon carved by the Colorado River over a period of roughly 6 million years. It is nearly 446 kilometers long and up to 1.8 kilometers deep. The canyon is considered one of the world's most significant geological sites because it exposes nearly two billion years of Earth's geological history through its colorful layers of rock, particularly the Vishnu Schist at the bottom. The 'Great Unconformity' is a famous geological phenomenon visible here, where a billion-year gap exists in the rock record between different layers. The canyon is so large that it creates its own weather; the temperature can vary by more than 25 degrees Fahrenheit between the rim and the river floor. It remains a central landmark for several Native American tribes, including the Havasupai, who still live within a tributary canyon.