104 
GEOLOGY. 
November 20.— Salt Creek .—We encamped on the border of this creek,, and remained all day to 
rest the mules. Two men were sent forward to look for the wagon road, and returned in the 
evening with the report that it was about 20 miles distant. The rays of the sun were very hot, 
and the thermometer stood at 90° during the middle of the day. Some small specimens of 
silicified wood were found on the surface, and a perforated marine shell—a Pecten —which had 
probably been dropped there by an Indian. A small hut regular rhombohedron of calcite was 
also found. This was perfectly clear, like Iceland spar, and was a perfect crystal, not being 
obtained by cleavage from a larger mass. The barometer at this camp stood at 30.4 inches for 
most of the time, thus indicating a depression below the sea-level—if 30 inches be regarded as 
the height of the mercurial column at that level. The ground towards the north and northwest 
was much lower, and there seemed to be little doubt that we were lower than the tide-waters of 
the gulf. 
November 21.— Salt Creek to the Emigrant Road , Carrizo Creek. —At daylight on the morning of 
the 21st we again set out for the emigrant road leading from the mouth of the Gila, and for 
Carrizo creek—the first water in the mountains after crossing the Desert. The surface over 
which we passed, from our camp, was principally the hard, blue clay ; but near the mountains it 
was covered up to different depths by the detritus of gravel and sand which had been brought 
down and spread out by floods, forming slopes of gentle inclination. 
Even the most level portions of the Desert in this vicinity have been much modified by the 
action of water. It appears to have re-assorted and distributed the argillaceous and sandy mate¬ 
rials of the surface, alternately cutting away and filling up, as was shown by the exposed roots 
of mezquite and other shrubs peculiar to that region. In some places these stood out two or 
three feet above the surface ; and at others they were buried to the same depth. If it were not 
for these bushes, the modification of the surface would not be perceptible, as it is singularly flat 
and level. Where the clay predominates, it is so smooth and hard that it does not afford a 
secure resting place for grains of dry sand; they are kept in constant motion by the wind, and 
have formed into long, parallel ridges or drifts, which appear to be progressing towards the 
southeast. These dunes or drifts were not deep ; the highest parts not being over ten feet above 
the underlying clay. They gave a gently undulating, wave-like outline to the surface. 
DESERT TO WARNER’S. 
As we approached the trail leading to Carrizo creek the surface became more uneven, and we 
passed over gravelly slopes, alternating with low and gently rising hills, covered with black, 
shining pebbles and rounded masses of volcanic rocks. The rocks and pebbles were spread over 
large areas, and appeared to be remnants of a drift deposit, older than the alluvial wash from 
the mountains. We also passed an isolated outcrop of granite, forming a slight knob in the 
plain, and trending north and south. 
The emigrant road was at length reached, and we turned a sharp angle towards the moun¬ 
tains, proceeding in a northwesterly direction, and ascending the slope of the desert. Many 
low hills, covered with black and shining pebbles and cobble-stones, were passed along the 
road, and soon, outcrops of thickly-bedded argillaceous sandstone were seen. The dip appeared 
to be towards the west. The road, on gaining the upper edge of the slope, made a sudden 
descent into the valley of Carrizo creek, which was then entirely dry. The sides of the valley 
are formed of horizontal, or nearly horizontal, strata of clay and sandstone, and the hill which 
we descended was bordered on each side by bluffs of red strata, containing gypsum in thin 
