792 
Journal of Agricultural Research 
Vol. XXVIII, No. 8 
A similar series showing the effect of altitude may be selected ranging from 
Indio near the Salton Sink to Idyllwild on the San Jacinto Mountains (fig. 20). 
Palm Springs and Indio differ very slightly in temperature, but Palm Springs 
has a heavier rainfall. Neither is sufficient to change the type of vegetation. 
The slight differences that exist are due primarily to topography and soils. 
Rainfall at Cabazon is approximately three times as heavy as at Indio and Palm 
Springs and the temperature about 8 degrees lower. The vegetation at Cabazon 
is of the chaparral type. Proceeding to the higher altitude of the yellow pine 
zone at Idyllwild, the rainfall is about ten times as heavy as at Palm Springs. 
The temperature is much lower, the average being about 52 degrees as compared 
with 65 degrees in the chaparral and 73 degrees in the creosote bush zone, although 
the temperatures do not fall below zero. The difference in average mean tern* * 
perature between the lower creosote bush zone and the yellow pine zone is approx¬ 
imately the same as between the same types at Maricopa and Williams. 
A similar series ranging from the Colorado desert northward (fig. 21) has been 
chosen. In this series, Indio represents vegetation consisting largely of desert- 
sage, although the climate is not essentially different in the creosote bush areas 
at a somewhat higher elevation. Las Vegas, Nev., has a vegetation composed 
of desert-sage and creosote bush at a higher elevation, with an admixture of 
shadscale. Therefore, Las Vegas may be regarded as near the northern limit of 
the southern desert. St. George, Utah, shows a vegetation characteristic of the 
northern desert, and represents almost the northern limit of the southern desert 
vegetation. At Parowan, Utah, the vegetation is typical of that of the northern 
desert. It consists of a great sagebrush area lying near the lower border of the 
juniper-pinon belt. Still another station, Yellowstone, may be chosen to 
represent conditions of sagebrush where it occurs close to the yellow pine zone. 
In comparing the rainfall of these five stations we find that Indio has a rainfall 
of less than 3 inches, and Las Vegas less than 4J inches, St. George has 9 inches, 
Parowan 13 inches, and Yellowstone Park 18 inches. On the conditions of 
moisture supply, therefore, the conditions improve as we pass northward, where 
there is also increase in elevation. Indio has an elevation of minus 20 feet, 
Las Vegas a little over 2,000 feet, St. George less than 3,000 feet, Parowan about 
6,000 feet, and Yellowstone 6,200 feet, a difference of more than 6,000 feet. 
Rainfall is more uniform at Yellowstone throughout the season, and it is the 
only station which has over £ inch precipitation during June. The temperature 
conditions are markedly different in these five stations. Indio has an average 
temperature of 73 degrees, Las Vegas 61 degrees, St. George 59 degrees, Parowan 
49 degrees, and Yellowstone Park 39 degrees. These differences in mean tem¬ 
perature are also accompanied by the similar differences in the maximum and 
minimum temperatures. The lowest at Indio is 16 degrees, at Las Vegas 8 
degrees, at St. George —1 degree, at Parowan —18 degrees, and at Yellowstone 
Park —41 degrees. Parowan and Yellowstone Park represent conditions in the 
northern desert area, therefore much colder, and have a much greater and more 
equally distributed rainfall than any of the stations in the southern desert shrub. 
On the basis of yearly summaries, the evaporation rate in this southwestern 
desert is high and the depression of the wet bulb is also high. 8 However, if 
only the period of growth is considered the conditions are by no means extreme. 
Briggs and Shantz 9 have found a close correlation between rate of transpiration 
1 Kincer, J. B. precipitation and humidity. Atlas of American Agriculture, Part II, Section A, Fig. 
103-105. 1922. 
• Briggs, L. J., and Shantz, H. L. hourly transpiration rate on clear days as determined by 
cyclic environmental factors. Jour. Agr. Research 5:583-650, illus. 1916. 
-. daily transpiration during the normal growth period and its correlation with 
the weather. Jour. Agr. Research 7:155-212, illus. 1916. 
