VALLEY OF THE LITTLE COLORADO. 61 
Shales and gypsum.—The crinoidal limestones capping the bluff at the western edge of the 
high mesa are succeeded in the ascending series by a group of green, white, and pink shales 
and gypsum, having altogether a thickness of nearly two hundred feet. The materials com- 
posing this group are very soft, and, yielding readily to the action of eroding agents, have been 
removed from all the western portion of the high mesa, with the exception of a few rounded 
buttes, one of which is situated on the extreme edge of the mesa south of our Camp 70, 
For five-and-twenty miles from the point where we ascended the upper mesa wall our route 
led over the rolling surface and through the pine forests already described. The surface rock 
is everywhere the crinoidal limestone, which at first rises gently, then falls off, with a rapid 
and uniform dip, into the valley of the Little Colorado, determining the outline of its eastern 
slope. 
VALLEY OF THE LITTLE COLORADO. 
The high mesa does not terminate on its eastern as its western border in a mural escarp- 
ment, but following the curve of the underlying rock the surface falls off in a nearly uniform 
slope of about one hundred feet to the mile for twenty miles. This slope is succeeded by a 
level plain, having a width varying from twenty to forty miles, and bounded on the east by 
mesas of different elevations. Towards the southeast, whence the valley has a perceptible 
descent, its eastern wall, though a marked feature in the landscape, is not more than one 
thousand feet in height. Near the mouth of the Little Colorado, however, the relative altitude 
of the mesa is increased by the depression of the surface of the valley, and its absolute altitude 
enhanced by the addition of two great steps or terraces to its surface. So that the angle of 
the mesa included between the Great and Little Colorados, on the north side of the latter 
stream, combining all the formations of the table-lands, and having an absolute altitude of eight 
thousand feet, overlooks the valley in a nearly perpendicular wall of some four thousand feet 
in height, of which the base is apparently washed by the waters of both streams at least six 
thousand feet below its summit. 
The valley of the Little Colorado, throughout its entire extent, is destitute of trees, and as 
we emerged from the dense pine forests of the mesa our eyes swept a hundred miles of its 
course, and we were able to grasp at a glance all the great features of its structure and relations 
to the country surrounding it. ' 
On the west the view was everywhere bounded by the forest-covered summit of the high 
mesa we had crossed, which stretched away in an unbroken line from the Colorado to the 
point where it was crowned by the snowy peaks of the San Francisco mountain and its sub- 
ordinates. On the eastern side of the valley the long lines of mesa walls, converging in 
perspective towards the southeast, filled the horizon and gave to the landscape that linear 
character so common on the table-lands, but never seen elsewhere. In the northwest the high 
mesa at the junction of the two Colorados formed a most conspicuous object; though at a 
distance of forty miles, subtending so large an angle and covered with a glittering sheet of 
snow, it resembled the line of a lofty and snow-covered sierra. 
The area intervening between the objects I have described seemed to us, for the most part, 
a smooth and grass-covered plain. Such it doubtless was at one time and nothing more; but 
subsequently, when we attempted to cross to the opposite side of the valley, we found that 
beneath its modest surface were concealed some of the grandest and most surprising physical 
features met with on our route, and impediments to our progress more insurmountable than 
any of the snow-covered mesas or mountains which then engrossed our attention and alone 
gave us any apprehensions. From the distance we could not see, what we afterwards dis- 
covered, that the plain was cut by a series of cafions searcely less profound than that of 
Diamond river, forming a labyrinth of difficulties effectually arresting our progress in the line 
we had hoped to follow. 
