The grand canyon was created over millions of years as the Colorado River cut through the land. What is this process called?

Grand Canyon is an awesome gash in the earth, running for about 200 miles (300 km) along the Colorado River in the northwest corner of Arizona. The Canyon is about a mile (1.6 km) deep, and about 10 miles (16 km) from north to south rims. The walls of the narrow, zig-zag inner gorge expose tilted and faulted Precambrian rock, while the walls of the outer and upper gorge are streaked with thick, colorful, horizontal bands of fossil-bearing rock, representing roughly the "bottom half" of the geologic column.