Credit: National Park Service. View full size image. The Grand Canyon is indeed a very big hole in the ground. It is 277 miles (446 km) long, up to 18 miles (29 km) wide and more than a mile (6,000 feet / 1,800 meters) deep. It is the result of constant erosion by the Colorado River over millions of years.t is 277 miles (446 km) long, up to 18 miles (29 km) wide and more than a mile (6,000 feet / 1,800 meters) deep. It is the result of constant erosion by the Colorado River over millions of years.