VEGETATION OF DESERT MOUNTAINS 293 



tains is made more simple than might be the case by the fact 

 that they are both in a relatively initial stage of physiographic 

 development, are both built chiefly of gneiss and both lie in a 

 WNW-ESE position. It is possible, therefore, to compare the 

 vegetation at the same elevations in the two mountains with 

 a minimum of complicating features, 3 and to determine the 

 influence of the greater altitude of the Pinaleno range in affecting 

 the character of its vegetation and flora. In making such a 

 comparison it is necessary to take into account the universal 

 influence of slope exposure, and also the influence on vertical 

 distribution which is invariably exerted by the elevation of the 

 surrounding country. 



The Pinaleno Mountains may be pictured as a series of rolling 

 areas surrounded on all sides by steep ridges and narrow canons, 

 falling away to the flood plain of the Gila on the northeast and 

 to the Bonita, or Sulphur Spring, valley on the southwest. 

 The length of the range is about 28 miles if we disregard the 

 chain of foot-hills that stretches southward toward the Dos 

 Cabezas range. Some of the most salient physical features of 

 the mountain are determined by the fact that on its northeastern 

 side its drainages reach the Gila at elevations of about 2600 feet, 

 and on the southwest side its streams fall to the Bonita valley 

 at only 5000 feet. On the side of the mountain facing the Gila 

 River steep alluvial fans, or bajadas, 4 have been deposited. All 

 of the large streams have cut through these bajadas so that their 

 upper courses now lie through rocky canons with V-shaped bottoms 

 and their lower courses through shallow canons in the outwash 

 material, with broadly U-shaped bottoms. A section of one of 

 the bajadas cut parallel to the face of the mountain would exhibit 

 a level top with pronounced edges and sides falling away in 

 parabolic curves. The average distance from the Gila River 

 to the true base of the mountain is about 6 miles. The longest 



3 The vertical limits of species and of vegetations are different on mountains 

 of different mineralogical character. In general, desert species reach higher 

 elevations on volcahics than on gneiss and the highest elevations on limestone. 



4 This Spanish word, which has been quite generally adopted into the vocabu- 

 lary of physiographic terms, should be pronounced bahdtha. 



THE PLANT WORLD, VOL. 22, NO. 10 



