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.
