There is a great group of table-lands constituting a geographic unit
which have been named the Terrace Plateaus. They ex-tend from the Paria
and Colorado on the east to the Grand Wash and Pine Mountains on the
west, and they are bounded on the south by the Grand Canyon of the
Colorado, and on the north they divide the waters of the Colorado from
the waters of the Sevier, which flows northward and then westward until
it is lost in the sands of the Great Desert. It is an irregular system
of great plateaus with subordinate mesas and buttes separated by lines
of cliffs and dissected by canyons.

In this region all of the features which have been described as found in
other portions of the province are grouped except only the cliffs of
volcanic ashes, the volcanic cones, and the volcanic domes. The volcanic
mountains, cinder cones, and coulees, the majestic plateaus and
elaborate mesas, the sculptured buttes and canyon gorges, are all found
here, but on a more stupendous scale. The volcanic mountains are higher,
the cinder cones are larger, the coulees are more extensive and are
often sheets of naked, black rock, the plateaus are more lofty, the
cliffs are on a grander scale, the canyons are of profounder depth; and
the Grand Canyon of the Colorado, the most stupendous gorge known on the
globe, with a great river surging through it, bounds it on the south.

The east-and-west cliffs are escarpments of degradation, the
north-and-south cliffs are, in the main, though not always, escarpments
of displacement. Let us understand what this means. Over the entire
region limestones, shales, and sandstones were deposited through long
periods of geologic time to the thickness of many thousands of feet;
then the country was upheaved and tilted toward the north; but the
Colorado River was flowing when the tilting commenced, and the upheaval