The Grand Canyon is a gorge created by the Colorado River. A gorge is a steep-sided river valley created by the erosive power of water. The Grand Canyon was carved into the Colorado Plateau by the Colorado River over millions of years.
The Grand Canyon is 277 miles (446 km) long and averages 4,000 feet (1,220 m) deep. The Grand Canyon is 6,000 feet (1,830 m) deep at its deepest and 18 miles (29 km) across at its widest.
The Grand Canyon is located in the northwest corner of Arizona near the borders of Nevada and Utah in the United States. The Grand Canyon sits on the Colorado Plateau. The Colorado Plateau is a region that covers 130,000 square miles (336,700 square km) in four states; about 90 percent of the plateau is drained by the Colorado River and its tributaries.
Geologists estimate that the Grand Canyon had its beginning about 5 million years ago when the Colorado River began its course across the Colorado Plateau from its origins in the Rocky Mountains. The Colorado Plateau is made up of layers of sedimentary rock including limestone, sandstone, and shale. It sits above the Earth’s tectonic plates which are made of very hard igneous and metamorphic rock.
The Colorado River falls more than 10,000 feet on its way from the Rocky Mountains to the Gulf of California. As it falls, the water increases speed and scours the rock, deepening and widening the river channel. The erosive power of the Colorado River has exposed layers of ancient rock. The layers of rock at the bottom of the Grand Canyon are nearly 2 billion years old. They were buried for hundreds of millions of years before the river cut into them. Each layer of rock has put up a different level of resistance to the river.
The layers of igneous and metamorphic rock at the bottom of the Grand Canyon–the oldest rock in the canyon–were formed by molten mixtures of minerals nearest the core of the Earth billions of years ago. Erosion of these rocks is very difficult. As a result, this is where the sides of the Grand Canyon are narrow and steep. Above this ancient rock, the younger sedimentary rock–formed by the collection of sand, mud, and sediment–is much softer and more easily washed away. This accounts for the wider and shallower slopes of the Grand Canyon nearer the top of the plateau.
As long as the Colorado River continues to flow, the Grand Canyon will continue to deepen and widen.