<P> The base level and course of the Colorado River ( or its ancestral equivalent ) changed 5.3 million years ago when the Gulf of California opened and lowered the river 's base level ( its lowest point ) . This increased the rate of erosion and cut nearly all of the Grand Canyon 's current depth by 1.2 million years ago . The terraced walls of the canyon were created by differential erosion . </P>
through what process has the colorado river created the grand canyon in the usa
erosion