58 Colorado Experiment Station 
SUMMARY 
The Rio Grande flows for about 60 miles through the San Luis 
Valley without any considerable change in the character of its waters. 
The flow of the river diminishes rather than increases in its pas¬ 
sage through the valley. 
There are only a few streams having a visible discharge into the 
Rio Grande. 
The drainage is practically out of the Rio Grande into the valley, 
instead) of out of the valley into the Rio Grande. 
The ground-waters of the valley retain the characters of the 
mountain waters in a noteworthy degree. 
The ground-waters, though retaining some of the features of 
mountain waters, have their own characteristics which are pronounced 
enough to affect those of the Rio Grande water if any significant vol¬ 
ume of them is mingled with it. 
The alkalis, i. e., salts that collect in the surface portions of the 
soil or appear as efflorescences, are of three types which are not fur¬ 
ther discussed. 
These types are: 
Plain sulfates, soda and lime being the predomi¬ 
nant bases. This type is the predominant one. 
Sulfates and chlorids. This type is not abundant 
though it is well distributed. 
A type in which sulfates and carbonates occur. 
The occurrence of this type is for the most part con¬ 
fined to the area north of the Rio Grande. 
Solutions of these alkalis do not find their way into the Rio 
Grande in sufficient quantities to noticeably modify the composition of 
its water. 
The valley is an exceedingly large artesian basin, but the waters 
are of two characters. Those of the southern portion and the rim of 
the basin are white and carry an excess of acids. Silicic is especially 
high, while those of the northern interior portion of the basin are al¬ 
kaline and usually brownish or brown in color. 
The white artesian waters, especially those flowing from shal¬ 
low wells, from 75 to 300 or even more feet, are very similar to river 
or mountain water and would simply increase the volume and would 
not change the character of the river-water if they mingled with it. 
The brown water is free from silicic? acid and contains so good 
as no salts except sodic carbonate. 
This character of the brown waters is the same for all flows from 
the shallowest to the deepest examined, 880 feet. 
The deeper flows increase in the amount of salts held in solution 
without any change in their character. 
This increase was from 22 grains to 108 grains in each imperial 
gallon. 
