Semi-arid Portion of Southwestern New Mexico. 243 



overstocking had reduced the vegetation cover the first floods 

 began to come, and have been coming with increased fre- 

 quency and violence every year since. 



Having found from an inductive study that the trenching 

 and other conditions of the valleys might be explained by a 

 removal of vegetation cover, and having found from the his- 



Fig. 3. 



Fig. 3. Typical recent stream trench in the Mangas valley, 

 alluvial valley filling in which the trench is cut. 



Note the flat 



Fig. 4. 



Fig. 4. Another view showing characteristic recent stream trenching. 

 This is near the head of a small valley, hut the trench is well developed. 



