CLIMATE OF THE SANTA CATALINA MOUNTAINS. 61 
dryness of the three months preceding the taking of the first set of 
samples, together with the 25 days of rainless weather just preceding 
the taking of the samples, had reduced the moisture of the superficial 
soil to an amount which was near the minimum for the year, as repre- 
sented by the percentages for June. The percentages for June were 
all slightly lower than those for April. The reading of 5.2 per cent for 
the south slope at 5,000 feet in April is undoubtedly too high. The 
fall in moisture on the north slope at 7,000 feet from 9.2 per cent in 
April to 3.2 per cent in June is doubtless significant of the long reten- 
TasLe 7.—Soil moisture in the arid fore-summer at a depth of 15 cm. on north and south 
exposures at seven altitudes on the Santa Catalina Mountains. 
Elevation Average of 
‘aad ae ne 29, sae 11, ae Le se 20, the.three de- 
exposure. ; cs . terminations. 
3,000 south....... 2.5 2.3 1.2 2.0 
4,000 south....... 2.7 2.4 1.0 2.0 
4,000 north....... 3.2 2.8 1.5 2.5 
5,000 south....... 5.2 1.8 2.4 3.1 
5,000 north....... 3.8 1.3 5.5 3.5 
6,000 south....... 2.3 1.3 1.9 1.8 
6,000 north....... 5.1 2.3 3.0 3.5 
7,000 south....... 3.1 2.6 2.1 2.6 
7,000 north....... 9.2 3.2 4.1 5.5 
8,000 south....... ish 6.1 8.8 7.4 
8,000 north....... 8.1 14.5 11.3 
9,000 south....... aig 9.4 9.4 
9,000 north....... 27.9 °27.9 
The percentages are based on dry weight. 
tion of moisture derived from winter rains, characteristic of the forested 
elevations. In June the north slope at 8,000 feet had fallen to a slightly 
lower percentage of moisture than the north slope at 7,000 feet in April. 
Between May 15 and 20, 1914, another series of moisture samples 
was secured at the same localities and extended to the 9,000-foot 
station. The preceding winter had been slightly below the average in 
precipitation, but the rainfall for March had been above the average. 
At the time of the taking of the samples there had been no rains for 
six weeks. This series of percentages is similar to those secured in 
1911, and the three may be taken together as indicating the average 
soil moisture conditions of the arid fore-summer. 
A significant feature of all three of the series of moisture determina- 
tions is the fact that there is no appreciable increase of soil moisture 
up to an elevation of 7,000 feet, beyond which elevation there is a 
sharp rise in the percentages, particularly those for the north slopes. 
In other words, so far as the superficial soil moisture conditions are 
concerned, the arid fore-summer carries the desert up to the lower 
limit of the Pine Forest. 
One of the underlying causes of the importance of slope exposure 
for vegetation is revealed in a comparison of the percentages of soil 
