Hardly any other natural wonder on Earth is more impressive than the Grand Canyon. Over millions of years, the Colorado River has dug up to 1,600m deep into the rock and created a gorge that is almost 30km at its widest point. To protect large parts of the canyon, the US Government established a national monument in 1908, which became Grand Canyon National Park in 1919. In 1979, UNESCO finally declared the Grand Canyon a World Natural Monument.