What has caused the retreat of cliffs surrounding the Grand Canyon over time?

The retreat of cliffs surrounding the Grand Canyon is primarily attributed to erosion by the Colorado River. This river has played a crucial role in shaping the landscape over millions of years, cutting through rock layers and transporting sediments. As the water flows, it erodes the bedrock and banks, deepening the canyon and causing the cliffs to retreat gradually. The persistent movement of water, combined with sediment transport, contributes significantly to the ongoing erosion process, which is a fundamental geological force responsible for the canyon's grandeur and depth.

While human activity and earthquakes can affect landscapes, they are not the primary factors influencing the formation and retreat of the Grand Canyon's cliffs. Weathering from wind does occur, but it is not as impactful in this context as the direct erosion caused by the river itself. Overall, the Colorado River's continuous action is the key factor in sculpting and maintaining the canyon's features over time.