The Grand Canyon is likely between 5 and 6 million years old, according to most geologists and scientists. However, some theorize that the Colorado River began forming the Canyon nearly 17 million years ago. The Canyon continues to form, due to the ongoing erosion that the Colorado River causes.
Geologists and scientists can estimate the Canyon's age by studying its layers of sediment and the animals and plants trapped within this sediment. The Canyon, which is 18 miles wide, 277 miles long, and 1 mile deep, is one of the Seven Wonders of the World and a national monument. Visitors can hike to the floor of the Canyon, and they also can take raft and boat trips along the Colorado River.