DESERT REGIONS OF NORTH AMERICA. 39 
Islay, Ann. Astronomical Observatory, Harvard College, vol. 39, pt. 2, 1906, 
p. 287) and are also found in the desert of Seistan, Persia. These dunes 
are rarely over 15 or 20 feet in height, and a plantin the way of the crest of 
the dune may be destroyed before it is uncovered by the advancing wave 
of sand. 
Some of the woody plants exhibit many interesting capacities in the 
way of elongation of the stems with restoring curvatures, by which those 
encountering the thinner portions of the dune are enabled to survive the 
inundation even when it is greatly prolonged (plate 39). 
The principal trail, still in use across the mountains in southern Cal- 
fornia, cuts across the southwestern portion of the Salton Basin and 
up the Carrizo Creek drainage system, passing for many miles throughthe 
sand of this region. During periods of high winds and storms the amount 
of sand carried along is so great as to make travel impossible. During 
such storms the experienced traveler shelters his animals as securely as 
he may against the cutting wind, and watches his wagons to prevent any 
deposit of sand, which might quickly grow into a dune of respectable size 
and impede his departure from the place after the storm. 
The Carrizo slopes bear numerous seepages, or slow springs, and as the 
sand moves along some of it is wetted when it reaches such a spring 
and remains in place. To this small moist heap other particles become 
attached by moisture until a mound of some height may be formed, 
which affords lodgment for a few perennial shrubs such as the mesquite. 
The growth of these bushes serves to bind the sand stillfurther. The 
seepage may vary, or the wind, in conjunction with the sun, may dry out 
and move some of the sand, killing the shrubs. As a final result such 
dunes may be disintegrated, while others, still intact and serving as 
retreats for numerous desert rats and small rodents, will be encountered 
nearby (plate 4o). ) 
The bottom of the Salton Basin lies 286 feet below sea-level, and an 
ancient beach-line 20-30 feet above sea-level incloses it, showing unmis- 
takably that the basin at one time was filled with water. Furthermore,an 
examination of the gravelly slopes reveals great numbers of minor beach- 
lines, indicative of levels at which the water has stood for extended periods. 
According to concurrent testimony of geologists, this basin was at one 
time the head of the Gulf of California and was cut off by the deposition 
of silt from the river entering it from one side, since which time the occur- 
rence of water in the basin has been irregular. Until recently the flood- 
waters of the river overflowed the banks of the river and, spreading over 
the sloping alluvial plain, finally found their way into the basin in some 
volume, cutting indefinite channels here and there, the most prominent 
of which were designated as New River and Alamo River. These chan- 
nels did not begin as definite outlets from the river, and simply ran across 
the plain for some distance, then widened and terminated. The string 
