54 
GEOLOGICAL REPORT-THIRTY-FIFTH PARALLEL. 
saturated with salt, and Captain Whipple states that it was highly alkaline and effervesced freely 
with acids. This salt and carbonate of soda is doubtless derived from surrounding strata of 
Tertiary age. 
Moving sand — Sand-dunes. —Extensive fiel of dry sand, drifted by the winds, were encoun- 
tered on the western side of the fourth range, or mountains bordering the Soda lake on the east. 
Captain Whipple states that the surface of this sand was compact and hard—so hard that the 
train passed easily and rapidly over it. “ In the midst of this barren plain were low, isolated 
ridges of rocky hills, upon the northwest sides of which sand was piled nearly to the tops, show¬ 
ing the direction of the prevailing winds.” 1 
Mr. Marcou records the presence of sand on the opposite side of the Soda lake, and says that 
it rose upon the mountains on each side. Sand-dunes were afterwards found on approaching 
the Mormon trail. 
- Mountains between the Soda lake and the Mormon trail. —The eastern boundary of the Soda 
lake is a range of mountains which Mr. Marcou notes as the the fifth chain. At the base of 
these mountains, metamorphic rocks, porphyroid greenstone, and quartz veins were observed. 
These rocks appear to constitute the mass of the range. A deposite of “ drift” from eight 
hundred to one thousand feet in thickness was also observed. In this the pebbles were small, 
and were intermingled with sand, forming a conglomerate. (See notes, March 10.) Between 
Camps 146 and 147 metamorphic rocks and roseate porphyry were seen, and similar rocks were 
continuous to Camp 148. Mica schists and trap-rock were found along the river, near the point 
where the Mormon road diverges. At this place, or on the right hank of the stream, I myself 
observed the rocks carefully and found them to consist of highly laminated gneiss, succeeded 
on the west by compact granite, traversed in different directions by many large veins composed 
of feldspar and quartz. The gneissoid rock is evidently metamorphic, and the planes of strati¬ 
fication are nearly vertical. 
Mojave river to the Cajon Pass. —On leaving the Mojave river the line of the survey followed 
a long, gently ascending slope for about twenty-one miles, to the summit of the Bernardino 
Sierra. Near the river, bluffs of horizontal strata of clay and sand are seen. These are 
probably of Tertiary age, and they are overlaid by the more recent deposites which form the 
slope. This detritus or wash from the surrounding hills is composed of gravel and fine sand 
and clay. The gravel and sand are not rounded and siliceous as in the beds of streams, hut 
are angular, and result from the gradual disintegration of the surrounding granitic mountains. 
A great portion of it is, therefore, feldspar, and from its decomposition a soil is formed, rich in 
the mineral ingredients required by vegetation. In ascending this slope a manifest change is 
observed in the soil. It becomes much more coarse, and frequently fragments of rocks of con¬ 
siderable size are seen, while on the lower portions fine sand and gravel only are visible. This 
difference in the state of division of the ingredients of the soil is to be attributed to the same 
causes which have produced the slope—the transportation of the debris of the mountains by 
streams, which rise in the high ravines and pour out upon the lower ground at the base, 
depositing the heavier rocks and detritus on the upper portions of the slope where the current 
is the most rapid and forcible, and carrying the finer portions to a greater distance. 
Cajon Pass, in the Bernardino Sierra. —In ascending from the Mojave river to the Cajon Pass 
the road is upon the gravelly materials of the slope up to the very summit, which is itself 
composed of the rudely stratified materials flanking the mountains. At this point these 
materials form a bluff above five hundred feet high, which faces the south, or the Pacific slope of 
the mountains. No granitic rocks appear within more than half a mile of the crest of the pass 
where it is crossed by the road. On descending the bluff by a steep and winding road, outcrops 
of a coarse-grained feldspathic sandstone are found with the strata strongly inclined, and lower 
down the pass the strata rise into hills and present fine exposures. The inclination is about 
1 Captain Whipple’s Report, p. 123. 
