36 BOTANICAL FEATURES OF NORTH AMERICAN DESERTS. 
The desert conditions extend across the Colorado River and south- 
ward, including the mesas of western Sonora. To the southward the 
Colorado Desert proper passes into the Pattie Basin and the low Eastern 
coastal plain of the Peninsula of California, portions of which are of an 
extremely arid character. 
Chief interest centers in the Salton Basin and the region inclosed 
by the ancient beach-line, which is 20 to 30 feet above mean tidewater. 
Slightly above this, on the northern side of the basin, 1s exposed the edge 
of a clay stratum in the foothills of the San Bernardino Mountains which 
serves to bring to the surface all of the water percolating from the gravel 
above them. Along this ledge is a belt of palms (Neowashingtonia) 
(plate 35), which in some places follows the clay exposure so closely as to 
make a horizontal line in the landscape, while in other places the seepage 
collects in the mouths of canyons and below the clay in sufficient volume 
to support colonies or oases of this beautiful tree (plate 36). 
One of the most convenient points from which to visit the native 
palm groves of the Colorado Desert is the town of Indio. The San Ber- 
nardino Mountains, high and timbered in their main western portion, 
send out eastward for many miles into the desert a low timberless spur. 
Its parched rocky slopes seem, at the distance of a few miles, to be devoid 
of any vegetation whatever, but upon closer inspection are found to be 
sparsely dotted with bushes, like the plains portion of the desert. The 
canyons of this spur open out upon the valley in broad deltas of gravel 
brought down by occasional torrents. Just within the mouths of some 
of the canyons occur groves of a native fan-leaved palm (Neowashingtonia 
robusta). 
The ordinary diameter of the trunk is about 2 feet and the trees at 
full maturity are about 50 feet high. Most of the old trunks are blackened, 
apparently by fire. The younger trees retain their dead leaves for several 
years, folded downward over the trunk and forming a cylindrical mass 
about 8 feet through and sometimes 18 feet in height. As the trees 
grow taller the lower of these dead leaves fall to the ground, leaving a 
naked trunk with a head of green leaves at the summit and a collar of 
dead leaves just underneath. 
All,the trees seem to stand on the same general level, not far above 
the base of the range. A close inspection showed that they grew in a 
moist clay soil, incrusted with alkali. Apparently such rain as falls upon 
the mountains and sinks into the earth is caught upon this clay table 
and runs over it to the exposed margin, where for several miles it forms 
a line of miniature oases containing the palms and various plants charac- 
teristic of alkaline springs. These include mesquite bushes (Prosopis), 
salt-grass (Distichlis spicata), a rush (Juncus), a sedge (Cyperus), and an 
orchid (Epipactis gigantea). Within the canyon and upon the delta 
were found a few desert shrubs not met with earlier, the leguminous 
