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. 
Station. 1911. 1912. 1913. 1914. | Average. 
4,000 feet...]| +7.2 |........ + .1 1.6 | +1.9 
5,000 feet... ]........[... eee e fee e ween 8.1 8.1 
6,000 feet...) 12.5 |........ 7.6 7.6 9.2 
7,000 feet...) 16.1 |........ 11.1 14.0 13.7 
8,000 feet... |. ccs elec secsesfeonenees 20.1 20.1 
9,000 feet... ]........ SLak. - |sucnnsuve 20.8 25.9 
[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 
3,000 4,000 6,000 8,000 
T T ' 
7,000 9,000 
5,000 10,000 
U 
oO 
T 
{ 
A D 
30 \ N N i ! ! ! 
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), onthe 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 
