FORMATION AND EXTENT OF THE SAND-HILLS OF THE DESERT. 
241 
beauty of their wave-like outlines and the purity of the sand. It is free from fine, earthy dust, 
and being perfectly dry moves about before the wind like the dry sand that has been washed on 
an ocean beach. The color varies somewhat at different localities, but is generally a light buff 
or reddish yellow, similar to ordinary river sand. A large proportion of the grains are trans¬ 
lucent, and some are transparent; many are dark-red and appear to be carnelian ; others are 
black, green, and brown. The clear grains are mostly silicious, and the others are probably 
derived from the wearing of volcanic rocks. Small garnets are not uncommon, and in some 
places considerable black iron-sand is found. When the sand is mixed with water, and treated 
with hydrochloric acid, a brisk effervescence ensues, indicating the presence of a notable quantity 
of carbonate of lime. 
The grains present an interesting appearance when viewed with a microscope. All the little 
asperities and sharp edges are seen to be worn away, and their surfaces are rounded by attrition, 
so that many of the grains are perfect spheres. It is not difficult to find quantities of the 
spherical grains by bringing the eye closely to the surface of the ground, especially where gravel 
is abundant, as in such places the grains are much larger than on the sand-hills. I thus 
obtained a great variety of little polished spheres of quartz, agate, garnet, and a transparent 
green mineral, probably chrysolite. The color of the sand at Deep Well-is a little darker than 
that between Carrizo Creek and the Colorado, and is not quite so fine. 
The principal accumulations of the sand are at the following localities: Between Pilot Knob 
and Alamo Mocho ; between Carrizo Creek and Salt Creek ; at Deep Well ; in the Bernardino 
Pass ; and on the north side of the Desert, opposite Deep Well. 
The position of the principal of these accumulations will be found upon the geological map of 
the Desert, where they are indicated by the finely dotted spaces. 
The most formidable and extensive accumulation is that between Pilot Knob and the Alamo. 
This constitutes what has been known as the u Sand-hills of the Desertthe other localities 
being either insignificant, or being in unexplored places. This accumulation of sand-hills 
borders the emigrant road on the north side for several miles ; it is a part of a long crescent¬ 
shaped belt of sand, that extends from Pilot Knob to the vicinity of the Alamo. 
In passing from the Colorado towards the Pacific, the first sand-hills of this belt are seen at 
the Indian village, overlying the upper terrace. Nearer Cooke’s Well the sand has poured 
over the bank, as shown in the figure, so that it encroaches upon the road, and partially buries 
SECTION OF SAND-HILLS COVERING THE BANK. 
S, Sand, drifting from the north ; C, Clay and sand of the bank or terrace. 
some of the mezquite bushes. Beyond Cooke’s Well the sand falls over the terrace in a similar 
manner. In fact, the southern extent and range of the sand-hills of this belt is determined by, 
and coincides with, the bank or terrace constituting the margin of the upper or higher plain of 
the Desert. 
31 F 
