8 



SOILS OF THE SAN LUIS VALLEY, COLORADO. 



Destructive hailstorms frequently occur. A summary of available 

 weather records maintained at various points in the valley is as 

 follows : 



Average monthly temperature at stations in San Luis Valley. 1 







[Degrees Fahrenheit.] 



i From U. S. Geol. Survey Water-Supply Paper 240, Geology and Water Resources of the San Luis 

 Valley, Colo. By C. E. Liebenthal. 



Average monthly precipitation at stations in San Luis Valley. 



[Inches.] 



SOILS. 



The valley is a basinlike depression, treeless, and topographically 

 featureless. It is a desertlike plain of gentle, uniform slope, and 

 except near the inclosing ranges apparently flat and broken only 

 by miles of undeviating irrigation ditches. In the vicinity of the 

 valley trough the slope becomes insufficient to afford free drainage, 

 and a more or less permanently wet condition obtains over extensive 

 areas of the northern and middle portions, which are traversed by 

 no permanent stream and are in places characterized by shallow 

 basins without drainage and occupied by alkali lakes. 



The valley depression is partly filled with gravel, sand, and clay, 

 derived principally from volcanic rocks of the adjacent mountains 

 and deposited by the waters of a former lake or inland sea. This 

 formation consists mainly of alternating strata of blue clay and 

 water-bearing sand the source of an extensive supply of artesian 

 well water. The valley floor approaches the inclosing ranges by 

 gently increasing slopes, usually merging into mountain foot slopes. 



