The Grand Canyon is a steep-sided canyon carved by the Colorado River. The Grand Canyon is 277 miles (446 km) long, up to 18 miles (29 km) wide and attains a depth of over a mile. For six million years, the Grand Canyon has expanded with the help of the mighty Colorado River, and for centuries, people from all over the globe have traveled to gaze out over its red and orange grandeur. The canyon, river tributaries, and surrounding grounds are contained within Grand Canyon National Park, the one of the most visited tourist destinations in the world. In addition, the park has been a UNESCO World Heritage Site since 1979. There are two public areas of Grand Canyon National Park, the North and South Rims. The Grand Canyon South Rim is the most accessible section of the national park, with numerous places where visitors can pull over to admire the views.