26 THE ARTESIAN WELLS OF COLORADO, 
The source of the supply for the wells is to be found at 
no great distance, in the streams from the mountains 
which pour their waters into the sands of the western 
part of the valley, and to a lesser extent from the streams 
of the eastern side. These have gradually raised a delta 
of sand where they enter the plain, higher than the basin 
proper and consisting of the coarser debris which has 
been brought down. Farther out in the valley, the beds 
of clay begin. All of the smaller streams are entirely 
lost in these beds of debris, as the map shows. Of those 
which do not disappear, it would be interesting to know 
whether there is any marked diminution of their volume 
in passing over this absorbing area. Except in high water, 
the streams do not extend as far as the map indicates. The 
watershed of the smaller streams from the west, which 
entirely disappear, is some 460 square miles, of the 
Saguache and San Luis creeks about 1,300. The amount 
brought into the valley by means of these streams is 
unknown, but the ratio it bears to the area of the water¬ 
shed will be approximately the same as in the case of the 
Rio Grande. Through the courtesy of the State Engineer, 
we have been furnished with the discharge of the latter 
river for 1890, and by taking the area of the watershed 
from Hayden’s maps with a planimeter, we find that the 
discharge of the Rio Grande, as measured at Del Norte, 
corresponds to a depth of twelve inches very nearly over 
the whole watershed. Assuming the same depth as the 
amount flowing off from the smaller streams, their total 
flow would average about 330 cubic feet per second. An 
unknown amount comes from the San Luis and Saguache 
creeks and from the mountains of the east. If we assume 
that this may be as much more, as seems a reasonable 
estimate, the total amount available would be some 600 
cubic feet per second. 
