236 
THE GEAKD CASON DISTEICT. 
OEIGIN AJ^D CHAEACTEE OP THE LOAD TO BE TEAESPOETED. 
We may now turn our attention to the material brought into the canons 
constituting the load to be transported. Although the Colorado is a river 
which derives the greater part of its water and transported material from 
lofty regions at a great distance from the canons, it still receives a notable 
amount of sediment from the Plateau Country contiguous to its banks. 
And it is interesting to note the conditions under which this sediment is con- 
tributed. The region adjoining the great canons of the Colorado is so arid 
that it does not give rise to a single surface stream. The very few tributa- 
ries to the canons which carry water enough to be worthy of notice have 
their sources far away in much loftier and moister countries. The rainfall 
of the region in question is not known, but it is doubtless exceedingly small, 
and if it be stated at 4 inches per annum for the region draining laterally 
into the Glen and Marble Canons, this amount seems to be as large as pres- 
ent knowledge may justify. In the Grand Canon district it is probably 
much greater, though still very small when compared with fertile regions. 
On the Kaibab, though the amount has never been measured, it seems as if 
20 inches per annum would be a very low estimate ; but this locality is 
quite exceptional. Eains sufficiently copious to saturate the soil and set the 
gulches running are very infrequent, and, perhaps, do not occur oftener 
than half a dozen times every year. But when they do come the conse- 
quences are very striking. The rills and washes are thick with mud and 
sand, and the water is loaded to its utmost capacity. There is no vegeta- 
tion to form a sod and hold the earthy matters in their place. The instant 
a rill forms it is a rill of mud. The country being scored with numberless 
canons and steeply sloping gulches, the rills and streams are gathered 
together with marvelous rapidity and plunge furiously into these narrow 
chasms, where they rush along with prodigious velocity. The traveler in 
such a canon, who is admonished of the coming of a storm, cannot be too 
diligent in seeking a place of safety. The murmur of the falling rain is 
followed in an incredibly short time by the deafening roar of the torrent, 
which rolls madly down the chasm as if some great reservoir above had 
