THE DRAINAGE SYSTEM OF THIi KAIBAB. 
197 
channels are kept open; having large basins, which furnish water enough, 
even though it be in the form of intermittent supply, to maintain a canon 
and corrade its bed. This is seen to-day all over the Kanab and Uinkaret 
Plateaus. During the Pliocene the same obliterating process probabl}^ 
prevailed upon the Kaibab. 
If, then, the great number of drainage channels upon the plateau took 
their origin at the beginning of the glacial period, the park valley must be 
much older. But we could not well suppose that it oi’iginated during the 
arid period of the Pliocene in a climate which dries up rivers instead of 
creating them, and we must therefore go farther back. It seems plain that 
the river was running during the periods of the great denudation — during 
the Eocene and Miocene, or certainly during the late Miocene — and that 
it became extinct when this denudation had been nearly or quite accom- 
plished. The reasons for assigning this epoch to the beginning of the Plio- 
cene or thereabout have already been given. Thus we arrive at the same 
conclusion as before. In reaching it we may note by the way the satis- 
factory manner in which our first perplexity is removed concerning the 
relation — oi’, rather, want of relation — between the park valley and the other 
drainage channels. We could at first discover no solution of their origin 
which would apply to both. But when the topogi’aphical details had been 
mastered and grouped in the mind the true explanation seemed to stand 
forth clearly and unmistakably. And when the facts of the drainage were 
placed in relation with those of upheaval and again with those of climate, 
the whole took form and coherence and disclosed a history, the verity of 
which needs no better support than its self-consistency. 
The conclusions drawn from the study of the Uinkaret now appear to 
be confirmed by the study of the Kaibab. We find certain facts common 
to both plateaus, and their I’elations and logical grouping are apparently 
identical. Both localities tell the same consistent story. Each, however, 
possesses features peculiar to itself. But the peculiarities in no respect con- 
flict; on the contrary, they contribute separate quotas of strong circum- 
stantial evidence of the verity of the main conclusions. 
Before closing this part of the subject it may be well to advert to the 
great amphitheaters excavated in the monocline on the east side of the 
