290 
COLORADO RIVER BASIN 
The uplifts were produced primarily by intense folding, rather 
than alone by vertical displacement. In the history of the science 
this disturbance is referred to usually as the Larimide Revolution. 
The Colorado River must have had its beginning prior to the 
completion of this mountain-building period, for its channel cuts 
directly through at least one of the ranges that had its origin at 
this time. It will be recalled that Green River, the principal 
tributary of the Colorado, rises in the Wind River Mountains of 
Wyoming, and flows in a southerly direction until just after it 
reaches the Utah-Wyoming , line. Then it turns suddenly to the 
east, and again to the south, where it cuts a mighty gorge directly 
through the Uinta Mountains. Evidence supports the interpre¬ 
tation that the river was in existence before the mountains were 
constructed and, therefore, that as the uplifting arose, the river 
simultaneously cut through the rising mass and thus maintained 
its course. 
It is clear, therefore, that at a time near the close of Cretacic 
time, the Colorado River Basin had already acquired somewhat 
its present outline. The lower depressions of the Basins, however, 
were frequently covered by more or less continues bodies of 
water, sometimes connecting with the Pacific Ocean near the point 
where the Colorado River now enters it. More commonly, how¬ 
ever, the Basin seems to have been devoid of extensive bodies of 
water, except in the form of playas and marshes. If to this 
picture is added the presence of lofty mountain on nearly every 
side of the Basin, we have a fair conception of the general con¬ 
figuration of the region. 
Under conditions such as these, the universal tendency of the 
eroding agencies is to wear down the higher elevations and fill 
up the lower ones. The streams flowing from these ancient 
mountains carried their loads of gravel, sand and finer materials, 
and spread them out over the valley floor. The gravels were 
dropped near the flanks of the mountains, the sands farther out, 
and still farther out the clays and muds. Taken as a whole, 
however, the materials are predominantly of the continental type. 
Moreover, as should be expected, they grade from coarse to fine 
from the peripheral parts of the basin inward. 
Plainly, deposition within this ancient Basin could take place 
