THE VOICE OF THE DESERT 



152 



once were. The desert valley is usually "fill" washed off 

 from the mountain's mass. Around the bases of the moun- 

 tains is piled the coarser debris in which they are slowly 

 burying themselves. These "talus slopes," as such collec- 

 tions of boulders and large stones are called, are among the 

 most distinctive features of the landscape, because only 

 where precipitation is low do even the larger fragments 

 from a decaying mountain remain so close to the slopes 

 down which they tumbled. Even so, many peaks in the 

 southern deserts still rise seven to nine thousand feet 

 above sea level, five or six above the deserts upon which 

 they are based. Many are higher than any summit east of 

 the Mississippi. 



All these mountains are relatively dry because higher 

 mountains lie between them and the seas from which 

 moist winds blow. But they are cooler than the deserts 

 and they also get more rain, squeezing the last moisture 

 out. of clouds which have managed to pass over the bar- 

 riers to the west or from moist air coming from the south 

 and leaving still less for the flat lands in their rain 

 shadow. From a distance . their flanks look almost bare, 

 but near the more humid summits they are often crowned 

 with pines. 



These mountains do much more than please the eye. 

 Every thousand feet means a perceptible change in tem- 

 perature and rainfall so that the mountains are responsible 

 for the fact, so surprising to the newcomer, that Arizona 

 is astonishingly rich in the number of different plants, 

 animals and birds native there. Yet most dwellers in the 

 larger towns are little more aware than town dwellers in 

 other lands usually are of the biota of which they are a 

 part. To them the mountains, ff they mean anything. 



