The Colorado River takes approximately one million years to erode just one inch of the Grand Canyon's rock at its deepest point.

The Grand Canyon's formation is driven by a process called downcutting, where the Colorado River erodes the bedrock of its channel. While the river flows at speeds of up to 20 miles per hour during floods, the sheer hardness of the metamorphic and igneous rocks at the canyon's base—such as the Vishnu Schist—makes erosion incredibly slow.The Colorado River began its current path roughly 5 to 6 million years ago. Since then, it has carved through nearly 6,000 feet of rock, meaning the average rate of vertical erosion is roughly one inch every 1,000 years. However, in the hardest, deepest layers of the Inner Gorge, erosion slows dramatically, approaching one million years per inch. The canyon's width, which reaches up to 18 miles, is caused primarily by side-stream erosion and mass wasting rather than the river itself.The rock at the bottom of the canyon is approximately 2 billion years old, representing nearly half of Earth's total history. Geologists from the National Park Service estimate that the river deepens the canyon by about the thickness of a piece of paper each year. The Grand Canyon Monitoring and Research Center (GCMRC) uses advanced GPS and laser mapping to track these minute changes in the canyon's topography. Their data confirms that while the river carries an average of 30,000 tons of sediment daily, the actual deepening of the solid rock floor remains one of the slowest natural processes on the planet.