May 24 , 1924 Significance of the Southwestern Desert Vegetation 723 
COACHELLA VALLEY 
PHYSIOGRAPHY 
Coachella Valley, Calif, (fig. 1), lies between the San Bernardino Mountains 
on the north and east, and the San Jacinto and Santa Rosa Mountains on the 
south and west. The lower part of the valley bordering the Salton Sea has a 
very gradual slope. The upper part forms a plain that rises rapidly toward 
San Gorgonio Pass. The Coachella Valley is approximately 50 miles long, and, 
at the edge of the Salton Sea, 11 miles in width, the width gradually diminishing 
toward the north. The rise is quite abrupt on each side, making the uppe, 
zones of vegetation, creosote bush or creosote bush and bur-sage, very narrowr 
excepting the broad alluvial fans at the mouths of all the canyons opening into 
the valley. In places, as at Coral Reef, these zones practically disappear. The 
uniformity of the slope is broken north and west of Indio, Calif., at the highest 
water line by a series of large sand dunes, which separate the upper higher plain 
from the lower and more level part of the valley. 
The lower part of Coachella Valley was at one time covered by a large body 
of fresh water, and later probably by the sea as an extension of the Gulf of Cal¬ 
ifornia. Full discussions are given by Blake (1858) 4 and Free (1914) 3 . The area 
is shown on the map by the sealevel line, and includes approximately all that 
part of the valley below Indio. Evidences of the former presence of water are 
still to be seen in the countless numbers of shells strewn over the surface of the 
soil of this area and also in the deposits of tufa on the rocks as at Coral Reef. 
SOILS 
The soils of Coachella Valley are derived from the surrounding mountains. 
They are mainly of granitic origin, but some are derived from shale and sandstone. 6 
The texture ranges from dune sand to clay loam. The two extreme types cover 
only small areas. The most prevalent types are a fine sandy loam and Fresno 
sand. The sandy loam occupies the lower part of the valley, while the Fresno 
sand forms the fans of alluvial soil at the mouth of canyons. The soils are gen¬ 
erally light in color and porous. Even where the heavier soils occur on the surface 
there is usually a lower stratum of coarse sand or gravel. The lower part of the 
valley between the city of Coachella and the edge of the Salton Sea has heavy 
deposits of alkali. Here the water table rises high enough to keep the surface 
of the soil moist practically throughout the year. Alkali also occurs along the 
beds of some of the creeks and on the small areas of very heavy soil scattered in 
the upper part of the valley. 
SALINITY 
The salt content of the soils in Coachella Valley varies from barely appreciable 
amounts to thick white crusts on the surface. The variation in the salt content 
and in its composition is often great in very short distances, and complicates the 
interpretation of the plant growth. If lands of arrowweed, pickleweed, and salt- 
grass are selected so that the total salt content of the soils are about the same, 
the arrowweed land would be preferable because of the preponderance of sul¬ 
phates rather than chlorids or carbonates as is apt to be the case in the pickleweed 
or saltgrass land. For instance, of two excessively saline locations about 100 
feet apart in the dry bed of a creek, one was covered by a rank growth of arrow- 
< Blake, W. P. bepobt op a geological beconnaissance in caufobnia. 370 p., illus. New York. 
1858. 
• Fbee, E. E. sketch op the geology and soils op the cahuilla basin. In MacDougal, D. T. f 
The Salton Sea, p. 21-33, illus. 1914. (Carnegie Inst. Wash. Pub. 193.) 
• Holmes, J. G. soil sub vet op the indio abea, caufobnia. U. S. Dept. Agr. Bur. Soils, Adv. 
Sheets Field Oper. 19Q3, Indio soil map. 1904. 
