American Forest Congress 95 



at the sources of mountain streams, ultimately brings 

 about a very different physiographic configuration from 

 that of non-forested areas under otherwise similar 

 conditions. In well timbered mountain summits and 

 ridges are usually broad and rounded. On the other 

 hand, non-timbered summits and ridges are inclined to 

 be sharp and jagged, with very precipitous slopes. The 

 former have a convex physiographic form, while the 

 latter have a concave. This condition can be observed 

 in all the mountain ranges of the West. Even in the 

 same range, these features above or below timber line 

 have sharp ridges and concave lines, while in the dense 

 timber the ridges are rounded and the form is convex. 



I am well aware that convexity in physiographic 

 form is indicative of youth, while concave physio- 

 graphic form indicates age. Although in a broad way 

 this is true, the concave or old type is reached at a com- 

 paratively early age on elevations that do not bear a 

 forest cover, while it is almost indefinitely postponed 

 on elevations that sustain an uninterrupted forest 

 growth. 



The convex configuration of forested summits and 

 ridges is the ideal type for the retention of a maximum 

 amount of the precipitation on the higher portions of 

 the drainage basin to ultimately seep through the soil 

 and give the streams a sustained flow. 



The concave configuration, which is so character- 

 istic of non-timbered mountains, permits the precipi- 

 tation for the most part to escape over the surface, not 

 only on account of the absence of an absorbing me- 

 dium, but because of the more precipitous slopes. 



The former condition causes a large percentage of 

 the rainfall to be retained at high elevation from 

 whence, through seepage, it gives perennial flow to 

 mountain streams. The latter condition results in the 



