CLIMATE OF THE SANTA CATALINA MOUNTAINS. 



75 



chiefly to its location on an extensive elevated plateau and to its 

 proximity to the cold-air flow from the San Francisco Peaks and other 

 neighboring elevations. 



It may be said, in general, that the frostless season is longer on the 

 ridges of an isolated mountain than it is in adjacent valleys at the 

 same elevations. Although the advent of spring at Cochise and Fort 

 Huachuca is earlier than on the mountains, the arrival of autumn is 

 earlier also, so that these two stations show an equality in length of 

 frostless season with the mountain ridges without a correspondence 

 with them in the dates of commencement and close. 



NORMAL ALTITUDINAL TEMPERATURE GRADIENT. 



The temperatures which have been secured on the Santa Catalinas 

 do not form an altogether satisfactory basis for the determination of 



Table 13. — Average differences between all observed minimum temperatures at stations situ- 

 ated on ridges in the Santa Catalina Mountains and the minima for the same days or 

 periods at the Desert Laboratory. 



[The plus sign indicates a higher temperature at the mountain station.] 



the normal altitudinal gradient, a datum which should be derived from 

 extended series of mean temperatures. However, in the absence of an 

 ideal collection of records from the several altitudes these imperfect 





Fia. 16. — Graph showing altitudinal fall in temperature in the Santa Catalina Mountains 

 (A), and lines showing rate of fall in free air (E) on Pike's Peak (C), on the Sierra 

 Nevada (D), and average rate for 17 extra-tropical mountains (B). 



data have been used as the basis of an approximate determination of 

 the gradient of fall of temperature with increase of altitude. The 



