Grand Canyon National Park, located in northwestern Arizona, is the 15th site in the United States to have been named as a national park. The park’s central feature is the Grand Canyon, a gorge of the Colorado River, which is often considered one of the Wonders of the World. The Grand Canyon, including its extensive system of tributary canyons, is valued for its combination of size, depth, and exposed layers of colorful rocks dating back to Precambrian times. The canyon itself was created by the incision of the Colorado River and its tributaries after the Colorado Plateau was uplifted, causing the Colorado River system to develop along its present path. The primary public areas of the park are the South and North Rims, and adjacent areas of the canyon itself. The rest of the park is extremely rugged and remote, although many places are accessible by pack trail and backcountry roads. The South Rim is more accessible than the North Rim and accounts for 90% of park visitation.