May 24,1924 Significance of the Southwestern Desert Vegetation 
725 
SALINITY 
The saline soils in the Gila Valley are confined largely to the areas where there 
is seepage or where the water table is high, as, for example, in the Atriplex len¬ 
tiformis (Torr.) S. Wats, (saltbush) areas. Often considerable areas of saline 
land are found in the low places to which the salts have been washed by flood 
waters. Such are the bare flats and Dondia (seepweed) areas. Occasionally there 
is sufficient salt at the surface to form a crust especially in the Atriplex lenliformis 
areas. Of the salts composing the saline material, the chlorids are the most fre¬ 
quent and most abundant (Table II). The sulphates are next in importance. This 
Table II.— Chemical analyses of soils at Chandler, Arizona, 1915 6 
[Results given in parts per 100,000] 
Plant growth 
Depth of sample 
© <o 
i 
arbonates 
icarbonates 
•3 
S 
3 
Xfi 
<S> 
4-3 
C8 
A 
& 
3 
! 
! | 
o 
03 
I 
8 
1 
! 
o 
M 
<o 
1 
CQ 
1 
3 
o 
CQ 
o 
co 
O 
co 
S 
EH 
Atriplex lentiformis 
Composite sample first, 
second, third, .fourth 
9 
0 
83 
201 
74 
26 
0 
169 
532 
(saltbush). 
feet. 
Atriplex lentiformis. 
Composite sample first, 
second, third, fourth 
10 
Trace. 
145 
90 
74 
0 
0 
149 
432 
Bare flat. 
feet. 
Composite sample first, 
second, third, fourth 
11 
0 
48 
910 
240 
195 
35 
450 
40 
1,990 
feet. 
Mesquite thicket 
Composite sample first, 
second, third, fourth 
12 
0 
102 
292 
224 
Trace. 
0 
338 
958 
(Prosopis glandu- 
iosa). 
feet. 
Atriplex polycarpa 
(desert-sage). 
Composite sample third 
and fourth feet. 
13 
0 
86 
360 
117 
37 
0 
279 
892 
° Analyses made by the Bureau of Soils, United States Department of Agriculture. 
6 See also: Means, T. H. sou. survey in salt river valley, Arizona. U. S. Dept. Agr. Bur. Soils, 
Rpt. Field Oper. 1900: 287-332, illus. 1900; and: Eckmann, E. C., Baldwin, M., and Carpenter, 
E J. soil survey of the middle gila valley area, Arizona. U. S. Dept. Agr. Bur. Soils, Adv. 
Sheets Field Oper. 1917, 37 p., illus. 1920. 
order is reversed in the Coachella Valley, where sulphates predominate. The 
bicarbonates, according to Table II, form a greater percentage of the salt content 
than in the Coachella Valley. This is also shown in an analysis by the Bureau 
of Soils (Table III). 
The vegetation and soil conditions in the vicinity of Casa Grande, Ariz., were 
also studied. The salts of the soils at Casa Grande (Table IV) show more 
sulphates than chlorids, and in this respect resemble the salts of Coachella 
Valley. 
VEGETATION 
COACHELLA VALLEY 
The plant communities in Coachella Valley are usually sharply differentiated, 
particularly those occupying the lower areas where the soil is comparatively 
well supplied with moisture for growth and contains large quantities of alkali 
salts. The uplands which are occupied by alkali-avoiding and more drought- 
evading species, are characterized by a more mixed vegetation. No attempt is 
made to distinguish the smaller plant communities, which are not as marked in 
the vegetation of the shrubby desert formations as they are in the grass formations. 
The associations, however, are much more uniform in composition and are often 
dominated by a single species. 
