6 Colorado Experiment Station 
area includes the towns of Leadville, Buena Vista and Salida. The 
conditions, however, have not been such as to materially change the 
character of the water. The sample of water taken about 120 miles 
further down the stream, was wholly return water, namely, irrigating 
water that had been applied to thefland and had found its way back 
into the river’s course. At the time that this sample was taken, no 
river water was flowing past Rocky Ford, the point at which the sam¬ 
ple was taken, for all of the river water had been diverted into the va¬ 
rious irrigating canals or ditches. The differences shown in the two 
cases, those of the Poudre and Arkansas river waters, are wholly quan- 
tative; the changes shown are identical in kind. 
The waters of the South Platte have been studied but to a less 
extent than those of the other streams. The conditions obtaining in 
this case are somewhat different from those obtaining in the cases of 
the Poudre and Arkansas. Still, the results obtained agree in show¬ 
ing that the changes produced in the character of the solids held in 
solution are the same as in the cases previously given. 
These changes are thorough-going; in the mountain waters we 
have the carbonates of lime, magnesia and soda predominating, while 
in the return waters we have these changed to sulfates and the quan¬ 
tity of these salts very greatly increased—ten times in the case of the 
Arkansas and forty times in the case of the Poudre water. 
These general statements evidently hold for the Laramie, for its 
waters are partly diverted into the Poudre without perceptible modi¬ 
fication of the results. They will probably hold for all of the streams 
of our arid regions where the conditions are similar to those obtaining 
in these cases; but it is not safe to assert that they will hold for all of 
our streams. 
CONDITIONS IN SAN LUIS VALLEY EXCEPTIONAL 
We recognize, on examining the water conditions ot the San Luis 
Valley, that they are exceptional. While the big features of the case 
may be very simple, there are others which are not, and the problem 
becomes, taken in its entirety, far more difficult to explain satisfac¬ 
torily than those of the eastern slope, where our problems of natural 
drainage and return waters are quite simple, and the changes in the 
waters of our streams are really such as should be produced by the 
waters entering them after flowing through adjacent higher-lying 
lands whether under cultivation or not. 
The Rio Qrande enters the San Luis valley a little north of the 
middle of the west side and flows southeasterly and south to the state 
line. We shall consider it only as far as the State Bridge, a distance 
of about 60 miles. 
