The final chapters of the geological history of the Colorado
Plateau involve huge changes, and a true scrambling of the
landscape by tectonic movements, and by erosional activity.
Volcanism has been an ever present entity during the Cenozoic
era. Each of these elements can be seen in the photo above, the
plateau's most famous gorge, the Grand Canyon. On the horizon is
the San Francisco Peaks volcanic field, which includes what may
have recently been the highest mountain in the contiguous United
States. The canyon (seen here from the less visited North Rim)
is an obvious monument to erosional forces, and a more subtle
monument to the work of tectonics. Most discussions of the Grand
Canyon emphasize the ancient nature of the rocks, but the very
appearance of the canyon bespeaks geological youth. Incredibly
steep canyon walls lining the river for more than 200 miles,
compared to an exceedingly flat canyon rim. The canyon is more
than a mile deep in places which means the Colorado River has
quarried and carried a