238 



-/. /.. Rich — Recent Sir,, mi Trenching in the 



the mountains, the permanent streams are of small consequence 

 except when swollen by the summer rains. 



In the following discussion when we speak of streams we 

 would be understood as referring to the temporary streams 

 which carry water only during, or immediately after, a storm. 



A conspicuous feature of the topography of the Silver City 

 quadrangle, outside the more rugged mountains, is a pro- 

 nounced stream trenching in all the valleys; a trenching of 

 recent date which is evidently still in progress. Along the 

 steep-walled mountain gorges this feature is, of course, not evi- 

 dent, but outside of the higher mountains it would be difficult 



Fig. 1. 



Fig. 1. View showing typical features along the course of the Cane 

 Spring Canyon stream across the piedmont fan. The photograph shows 

 recent trench in the foreground cut into alluvial valley filling, piedmont 

 gravels in the middle distance along the sides of the valley, and mountains 

 at source of the stream in background. Note the bowlders and flood debris 

 spread out over the surface of the alluvial flat. 



to name a valley in which it is not conspicuous. The features 

 shown in different parts of the quadrangle are so similar that a 

 description of one of the most typical valleys will serve as a 

 characterization of the general conditions throughout the area, 

 and as a basis for a discussion of the causes of the trenching. 

 For such a description the valley called Cane Spring Canyon, 

 along which some of the accompanying photographs were 

 taken, will admirably serve our purpose. 



The stream, which is a temporary one, flowing only in times of 

 flood, heads with several branches in a region of rocky hills of 

 moderate height. Within the hills it has a drainage area of 



