Deep trenches such as the Grand Canyon were formed primarily by erosion. In the Grand Canyon, the Colorado River gradually cut downward through layers of rock, while weathering, runoff, wind, ice, and landslides widened and shaped the canyon walls.
Erosion is the movement of broken-down rock and soil from one place to another. It differs from weathering, which breaks rock apart without necessarily transporting it. In a canyon, these processes work together: weathering weakens the rock, and flowing water carries sediment away.
The Grand Canyon is about 446 kilometers (277 miles) long and reaches depths of more than 1.6 kilometers (1 mile) in places. Its exposed rock layers preserve nearly two billion years of geological history, although the canyon itself is much younger than the oldest rocks visible inside it.
A common mix-up is to credit the canyon only to the river. The Colorado River was the main cutting force, but tributaries and long-term climate and geological changes also contributed. Uplift of the Colorado Plateau helped give the river enough gradient to cut deeply into the landscape.