COLORADO RIVER BASIN 
291 
only by reducing the height of the mountains surrounding it, or, 
stated conversely, as the mountains were worn down the Basin 
was filled up. Necessarily, the combined effect was to equalize 
the general elevation of the region. Evidence points to the con¬ 
clusion that this process continued until at least the greater part 
of all the higher peaks disappeared and the Basin was more or 
less filled. In certain places, especially near the flanks of the 
mountains, the deposits are assumed to reach several thousand 
feet in thickness. 
This vast leveling process occurred largely during Tertic times, 
near the close of which another geographical revolution occurred. 
This time the Colorado River Basin was lifted in its entirety, in 
places almost as gently as a mother lifts her sleeping babe. The 
Larimide Revolution was characterized by marked folding and 
plicating of the strata; but this one, near the close of the Tertic 
time, left the formations almost as nearly horizontal as when they 
were originally deposited. Only in isolated and local places were 
the strata arched into folds, and then only into gentle ones. Here 
and there, as in the region of the great Kaibab Plateau, the coun¬ 
try rose differentially, but this was accomplished largely by 
faulting the formations rather than by flexing them. It, of 
course, will be remembered that we are referring to the Colorado 
Basin of Utah and Arizona rather than to the Basin as a whole. 
In certain localities the uplifting was also characterized by intense 
volcanic activity. 
Thus, the series of events culminating with the revolution just 
mentioned, imposed upon the Colorado River a task almost Her¬ 
culean in its proportions. Up to this time the River, at its best, 
was scarcely more than a sluggish stream, slowly meandering 
toward the ocean; but simultaneous with the uplift, the grade of 
the stream increased, and gradually the River was transformed 
into a rushing torrent. Formerly the stream had been required 
to carry nothing more than a nominal load; but with its increased 
capabilities, incident to rejuvenation, it was confronted with the 
gigantic task of not only denuding the Colorado Basin of that 
which had previously been deposited within it but also of 
eventually carrying the entire country down to the level of the 
ocean, out of which it has previously risen. 
