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With layers of red, pink, purple, brown, green, gray, and yellow, the rocky walls of the Grand Canyon look like a box of melted crayons.
No powerful cranes, noisy drills, or enormous shovels constructed the canyon. Instead, it was created by the mighty Colorado River. Of course, it had some help: small streams and tributaries, plus wind, rain, snow, and ice, as well as Earth’s shifting tectonic plates.
The canyon is a slow and steady work in progress that has continued for more than 6 million years.
The Mighty Colorado
The strong waters of the Colorado and its tributaries carried along billions of gritty fragments. They included sediment—a mix of silt (powdered rock), gravel, mud, and sand—along with ice. The river was like a powerful tool that eroded the rock layers. It created the canyon’s basic form. The sandpaper action of the moving sediment deepens the canyon by about six inches every thousand years.
Explore the Grand Canyon
At 9,010 feet above sea level, the Colorado River begins in Rocky Mountain National Park in Colorado. The river is 1,450 miles long. As it enters the Grand Canyon at Lee’s Ferry, its altitude is just over 3,000 feet. At the lower end of the canyon, at the Grand Wash Cliffs, the river has dropped another 2,200 feet.
▲ Earth’s crust is made up of large slabs of rock, called plates. At one time, western North America was at or below sea level. About 70 million years ago, the Pacific plate crashed against and slid below the North American plate, creating a 130,000-square-mile area a mile high, called the Colorado Plateau. Aftershocks created the Rocky Mountains. The ancestor of the Colorado River, which had meandered over the plateau before the collision, began cascading downhill toward an outlet in the Gulf of California. That was the beginning of the Grand Canyon.
▲ The Colorado River can be as deep as 90 feet and as shallow as 6 feet. It has an average depth of around 20 feet. The river includes alternating sections of rapids and calm waters. The rapids generally occur in shallow areas, and the calm waters are usually found in deeper waters.
◀ Today, the river is bluish-green. Sediment and silt lie trapped behind the Glen Canyon Dam in Lake Powell. The dam, completed in 1963, has reduced the amount of water that flows into the Colorado River by about 90 percent.
