May 24,1924 Significance of the Southwestern Desert Vegetation 
759 
saline. The penetration of water in the rainy season is deep but the water 
table is beyond the reach of the root system. The growth here is scattered 
and open, the individual trees being smaller, scarcely forming a trunk and re¬ 
sembling large shrubs. 
The texture of soil indicated by the mesquite thickets is like that of the desert- 
sage land. Sample 14, Table XXVII, shows the first foot considerably lighter, 
because it was taken on a hummock, otherwise it would show heavier soil. The 
main difference in the two types of land is in the soil moisture. In the mesquite 
land the water table influences the soil moisture. The third and fourth feet 
were not found dry as late as October. In spring there is an abundance of water 
in all 4 feet. 
Salinity. 
The salt content is appreciable in all 4 feet and is especially high in the third 
and fourth feet (sample 14, Table XXVII). 
Summary of Physical Conditions Indicated 
The mesquite thickets indicate land with (1) a soil texture approximately 
that of desert-sage land; (2) water table high but never actually coming to the 
surface of the soil; (3) an abundance of available water in all 4 feet in spring, 
and some water in the third and fourth feet even late in fall; (4) an appreciable 
quantity of salt in all 4 feet, the quantity increasing in the third and fourth feet. 
ADAPTATIONS TO PHYSICAL CONDITIONS 
The mesquite has a very wide range of adaptability as to the soil conditions 
under which it grows, from a nonsaline type that is practically pure dune sand 
to the saline heavy adobe lands at the bottoms of the valley. It is on the latter 
type that the pure dense mesquite thickets occur, often so dense as to be almost 
impenetrable. 
The mesquite puts out a new set of leaves in the early spring and carries a 
dense foliage throughout the hot months. Most of these leaves are lost in the 
winter. Mesquite blooms in the spring, and in late summer or early fall bears 
ripe fruit pods which were used to a large extent as food by the Indians. This 
tree thrives best on a heavy soil that is subirrigated, and rarely forms a good 
sized tree on lands where its roots can not reach underground water. 
Mesquite thicket land covers considerable areas in the Gila Valley. This land 
is subject to flooding by the water from lands above, but could probably be used 
for growing crops after leaching out some of the salts without providing artificial 
drainage. 
NARROWLEAF SALTBUSH ASSOCIATION 
TOPOGRAPHICAL RELATIONS 
Narrowleaf saltbush ( Atriplex linearis S. Wats.), has a much more limited 
range than desert-sage. It is not found in Coachella Valley. In the Gila Valley 
it occupies the low flat depressions occurring either in the creosote bush or in 
the desert-sage areas. The center of these flat areas is either a “bare flat” (“slick 
land”) or a seepweed area. Surrounding this is the narrowleaf saltbush area 
and outside of this area again is a scrubby growth of creosote bush or desert-sage. 
At the lines of contact between these types are considerable areas of narrowleaf 
saltbush mixed with seepweed or desert-sage, and, more rarely, with creosote 
bush. 
BOTANICAL COMPOSITION 
Typical areas of narrowleaf saltbush (Atriplex linearis S. Wats.) contain no 
other shrubs. Usually Atriplex polycarpa (Torr.) S. Wats. Prosopis glandulosa 
