Since about 6 to 10 million years the Colorado river together with other erosive forces has been carving this spectacular gorge, which is up to 60 feet (1800 m) deep, up to 18 miles (29 km) across and about 220 miles (350 km) long. The colourful strata of the Canyon walls contain fossils from the earliest living on our planet and reveal invaluable information on the earth' evolution and history over two billion years.