Why is the Grand Canyon unique?

Located in Arizona and stretching to Colorado, the Grand Canyon is 18 miles (29 kilometers) wide, 227 miles (365 kilometers) long, and 6,000 feet (1,828 meters) deep in its deepest section. It takes about two days by foot or mule to travel from the top to the bottom. Although it is not the biggest canyon in the world—Barranca de Cabre in northern Mexico and Hell’s Canyon in Idaho are deeper—it is known for its amazing landscape. The canyon’s walls are made up of rocks, cliffs, hills, and valleys formed millions of years ago, and it is home to hundreds of species of mammals, reptiles, and birds. Although people lived in the canyon some 4,000 years ago, today it is a national park and national landmark.