302 



FORREST SHREVE 



It goes without saying that the rainfall record of a single 

 season is of relatively little value, but it has been impossible to 

 continue the observations on the Pinalenos and the data secured 

 are of too great interest to be discarded. The altitudinal curve 

 for the Santa Catalinas (fig. 6). closely approximates the form of 

 the average curve for a ten-year series in that mountain, showing 

 a sharp rise from the base, at 3000 feet, to the first mountain sta- 

 tion, at 4000 feet, a drop to the second station, at 5000 feet, and 

 a pronounced rise from 6000 to 7000 feet. There have been 

 several years when the rainfall at £000 feet on the Santa Cata- 



Fig. 6. Canopy of the forest on the summit of Mt. Graham at 10,500 feet. 

 The trees are chiefly Picea engelmannii. 



linas was less than at 8000 feet, and the question rose as to 

 whether 9000 feet was near the elevation at which the altitudinal 

 increase of rainfall ceases in this region. The aim of securing 

 data from the Pinalenos was (1) to determine whether the alti- 

 tudinal increase of rainfall has ceased at 10,000 feet; (2) to de- 

 termine the influence of the higher basal elevation of these 

 mountains in affecting the shape of the curve of altitudinal in- 

 crease; and (3) to discover whether the lowest station in the for- 

 est has here a markedly higher rainfall than the next station be- 

 low it, as is true in the Santa Catalinas. 



