Semi-arid Portion of Southwestern New Mexico. 239 



about seven square miles. After leaving the bills the stream 

 flows with an average slope of 120 feet per mile for about 5 

 miles across a dissected piedmont gravel accumulation to the 

 Mangas, a larger temporary stream which, about 15 miles 

 below, empties into the Gila, a good-sized permanent stream. 



The salient features of the Cane Spring valley in its course 

 across the piedmont gravels are well shown in the accompany- 

 ing photograph (fig. 1). There are first the steep-sided valley 

 walls of partly cemented desert conglomerate from 50 to 150 

 feet high ; then, forming the valley floor, comes an alluvial 

 flat, nearly level in cross section ; and finally, cutting sharply 



Fig. 2. 



Fig. 2. Recent stream trench woi-king back into the still undissected flat 

 of a small tributary of Cane Spring Canyon. This picture was taken near 

 the site of fig. 1. 



into the material of this flat, is the recent stream trench from 

 50 to 200 feet in width and from 2 to 15 feet in depth, and 

 bounded, as a rule, by vertical walls of alluvium. 



The history of the valley as revealed by its cross section may 

 be briefly summarized as follows : The valley was initiated on 

 the surface of the piedmont desert fan. Tor some reason — 

 an uplift of the land or a change in climatic conditions — the 

 stream began cutting through the fan. This cutting continued 

 until a valley from one-eighth to one-fourth mile in width and 

 locally over 150 feet in depth had been formed. Following 

 this period of cutting came one of filling, during which the 

 alluvial flats in the valley were formed. Lastly, the streams 

 began cutting again, forming the trendies whose origin we are 



