56 



VEGETATION OF A DESERT MOUNTAIN RANGE. 



Figure 6 gives the actual curves for the three summers for the Santa 

 CataUnas. It will be noted that in each curve there is a sharp rise 

 from 3,000 to 4,000 feet, a rise which continued at the same gradient 

 to 5,000 feet in 1911 and 1913. From these submaxima, reached at 

 5,000 feet in 1911 and 1913 and at 4,000 feet in 1912, there is a fall to 

 a subminimum at 6,000 feet in the two former years and at 5,000 feet 

 in the latter year. There is then a pronounced rise in the curve to 

 7,000 and 8,000 feet. The rainfall at 9,000 feet in 1912 was probably 

 an inch or more greater than indicated by the curve, in any case was 

 greater than that at 8,000 feet; whereas in 1913 the precipitation at 

 9,000 feet was less than that at 8,000 feet, in fact less than that at 

 5,000 feet. 



The horizontal distances between the rainfall stations were unequal 

 (see plate A), the angle of rise from 3,000 to 4,000 feet being very 



Fig. 7. — Graph showing vertical increase of summer rainfall in the Santa Catalina Mountains 



in 1911 (solid line), together with averaged vertical increase in a series of 13 Weather Bureau 



stations in Arizona (broken line). 

 Fig. 8. — Graph showing vertical increase of summer rainfall in the Santa Catalina Mountains 



in 1912 (solid line), together with averaged vertical increase in a series of 21 Weather Bureau 



stations in Arizona (broken line) . 



sharp, that from 4,000 to 5 000 slightly less sharp, and that from 5,000 

 to 6,000 still less sharp and exactly equal to the angle of rise from 6,000 

 to 7,000 feet. The stations at 8,000 and 9,000 feet are located at the 

 west end of the main ridge and are consequently not in line with the 

 lower stations. The sharp rise in elevation between the 3,000 and 4,000 

 foot stations is doubtless partially accountable for the rapid increase 

 of rainfall between them. The steep rise of the rainfall graphs between 

 6,000 and 7,000 feet may indicate an influence due to the position of 

 the 7,000-foot station on the north rim of Bear Canon, with a very 

 abrupt wall immediately below it. There is no topographic cause, 

 however, to which it is possible to attribute the dip in the rainfall 

 curves for 6,000 feet in 1911 and 5,000 feet in 1912. 



In order to institute a comparison between the mountain gradients 

 of rainfall and those of the valley stations of the Weather Bureau the 

 data have been collated which are expressed in the curves of figures 7 



