6 



SOILS OF THE SAN LUIS VALLEY, COLORADO. 



importance or permanence of flow. They are of higher gradient than 



' the west-side streams, usually head in glacial cirques, but cover only 



small drainage areas. The northern part of the valley trough is 



PIG. 1. Sketch map of San Luis Valley, Colorado. 



traversed for a distance of some 40 miles by San Luis Creek, rising 

 in the vicinity of Poncho Pass. Like the less pretentious streams 

 reaching the valley from either side, it is of inconsiderable flow. 



