738 
Journal of Agricultural Research 
Vol XXVIII, No. 8 
present a very uniform appearance. The bushes are regularly but widely spaced 
with the intervening ground covered with annuals. Where there is a good growth 
of the creosote bush covering large areas the plants are from 5 to 7 feet high, 
although scattered plants in very favorable locations attain a height of 10 feet or 
even more. A poor growth consists of low scraggy, open plants, 2 to 5 feet high, 
with a few branches sparsely covered with leaves. In the fall, when the moisture 
supply has been exhausted this growth is decidedly brown, while the good growth 
where moisture is still available shows dark green. The dark brownish-green of 
this association contrasts sharply with the light gray of the desert-sage association. 
PHYSICAL CONDITIONS INDICATED 
Soil Moisture 
The soil in this area in Coachella Valley is light and porous and is composed of 
coarse unweathered particles of rock. The moisture equivalents (Table VI) show 
that the moisture-holding capacity is low. The penetration of water into this 
soil is very rapid and much deeper than in the desert-sage. In March there is 
available water to a depth of 4 feet, while late in summer there is none at that 
depth. Creosote bush is never found on soils where the water table is high. 
Table VI.— Comparisons of spring and fall soil conditions at the same stations in 
typical creosote bush areas . Indio, Calif ., 1915 a 
Date of collection 
Date of collection 
Item 
Depth 
of 
soil 
Mar. 
2 , 
sam¬ 
ple 
No. 6 
Mar. 
2 , 
sam¬ 
ple 
No. 7 
Mar. 
2 , 
sam¬ 
ple 
No. 8 
Mar 
3, 
sam¬ 
ple 
No. 9 
Mar. 
3, 
sam¬ 
ple 
No.10 
Aver¬ 
age 
Sept. 
21 , 
sam¬ 
ple 
No. 6 
Sept. 
21 , 
sam¬ 
ple 
No. 7 
Sept. 
21 , 
sam¬ 
ple 
No. 8 
Sept. 
24, 
sam¬ 
ple 
No. 9 
Sept. 
24, 
sam¬ 
ple 
No 40 
Aver¬ 
age 
Moisture equiva¬ 
lent. 
Feet 
1 
3.8 
3.4 
4.2 
2.3 
2.6 
3.3 
3.7 
6.5 
3.6 
1.9 
2.8 
3.7 
2 
3.4 
2.6 
5.9 
3.0 
2.7 
3.5 
3.9 
8.0 
4.3 
3.3 
3.1 
4.5 
3 
3.4 
2.1 
2.9 
3.0 
2.8 
2.8 
4.0 
5.4 
3.6 
3.6 
3.0 
3.9 
4 
2.8 
3.1 
2.8 
2.1 
2.7 
2.7 
3.6 
6.5 
3.2 
2.9 
4.1 
4.1 
Wilting coefficient. _ 
1 
2.0 
1.8 
2.3 
1.3 
1.4 
1.8 
2.1 
3.5 
2.0 
1.0 
1.5 
2.0 
2 
1.8 
1.4 
3.2 
1.6 
1.5 
1.9 
2.1 
4.4 
2.3 
1.8 
1.7 
2.5 
3 
1.8 
1.1 
1.6 
1.6 
1.5 
1.5 
2.0 
2.9 
2.0 
1.9 
1.6 
2.1 
4 
1.5 
1.7 
1.5 
1.1 
1.5 
1.5 
2.0 
3.5 
1.7 
1.6 
2.2 
2.2 
Moisture content 
1 
+1.4 
+8.0 
+2.8 
+0.9 
+1.9 
+3.0 
-1.1 
-1.7 
-1.0 
-0.8 
-1.2 
-1.2 
above or below 
2 
+3.0 
+8.8 
+3.0 
+4.4 
+2.9 
+4.4 
-0.9 
-3.2 
-1.3 
-1.4 
-1.4 
-1.6 
wilting coefficient. 
3 
+4.3 
+5.0 
+3.5 
+6.9 
+2.4 
+4.4 
-1.6 
-1.8 
-1.3 
-1.3 
-1.1 
-1.2 
4 
+2.„6 
+0.9 
+1.9 
+3.3 
+2.8 
+2.3 
-1.4 
-1.7 
-0.7 
-1.2 
-1.6 
-1.3 
Salt content h . 
1 
<.01 
<.01 
<.01 
<.01 
<.01 
<.01 
.01 
<•01 
<.01 
.02 
<.01 
.01 
2 
<.01 
<.01 
<.01 
<.01 
<.01 
<.01 
.01 
<.01 
<.01 
.01 
<.01 
.01 
3 
<.01 
<.01 
.02 
<.01 
<.01 
.01 
.01 
<.01 
<.01 
.01 
<.01 
.01 
4 
.01 
<.01 
.02 
.02 
<.01 
.01 
.01 
.02 
<.01 
<.01 
<.01 
.01 
a All data in this table are stated in percentages of the dry weight of the soil. 
b Electrical resistance readings over 3,000 ohms indicated less than «) 0.01 per cent. 
In considering soil moisture conditions in the different associations reference 
should be made to figure 7 which shows the daily rainfall for three stations in 
Coachella Valley. It is evident at a glance that no soil moisture had been added 
during the summer of 1915 and that whatever growth the plants had made was 
due to the soil moisture present at the beginning of the growing season in March 
(Table VI). 
A comparison of the soil of the creosote bush land in Gila Valley with that in 
Coachella Valley shows (Tables VI and VII) the texture of the former to be much 
finer, with the moisture equivalents two or three times as high, which increases the 
