90 
GEOLOGY. 
at Cape St. Lucas. The following descriptions are accompanied hy a geological section, which 
will serve to give a general view of the geology. The profile is taken from the barometrical 
observations of the Survey. The outline and summit of Bernardino mountain is sketched in 
with its estimated elevation of about 9,000 feet. This mountain is on the north side of the 
Pass, and San Gorgono mountain on the south. 
November 13.—Leaving the camp near the house of Mr. Weaver, jr., we ascended the valley 
of a stream which has cut its way downwards below the general level of the slope. High banks 
of sedimentary accumulations hounded our way on the right and on the left. These are un¬ 
consolidated, and appear very recent, simulating those of the slopes of the Great Basin. No 
regularly stratified and firm sandstone was seen ; the materials seemed to he irregularly strati¬ 
fied and generally coarse. They were not, however, closely inspected, the favorable exposures 
being at a distance from the trail. The ascent continued very gradual; at length a short hill 
brought us to the edge of a broad and gently sloping plain, upon which an adobe house is built. 
This, although partly in ruins, was occupied hy Mr. Weaver, well known as an experienced 
mountaineer. He is the claimant of a large rancho at this place. The presence of fruit trees 
and other evidences of cultivation showed that the rancho had been in use for many years, and 
it is said that the occupants have several times been driven away hy the Indians. The situation 
of this rancho, and the house, is such as one would least expect, being at the summit of the pass. 
We passed a few miles beyond the house, and encamped on the eastern slope of the pass, at 
the side of a small mountain stream descending from the peak of San Bernardino. The hanks 
of the stream at that point were high, and were composed of drift or detritus ; no outcrops of 
granite or hard rocks were visible along its channel. The hills on the left at the northeast were 
rounded, and appeared to be sedimentary. 
We had thus ascended without any difficulty from the valley of San Bernardino to the sum¬ 
mit-level of the pass, and we found it entirely different in its character and appearance from any 
that were examined in the Sierra Nevada or the Bernardino Sierra. It can hardly be considered 
as a low ridge of the mountains, but appears as an absolute break or dislocation of the entire 
chain. It is wide and open, bounded on one side by the snow-capped Bernardino mountains, 
and on the other by the sharp, imposing peak of San Gorgono. The distance, north and south, 
between these mountains at the divide is from two to three miles, and the lowest ground 
appears to be at the base of San Gorgono. The ascent to the highest point from the Bernar¬ 
dino valley is gradual, and, as we have seen, over grounds capable of cultivation, and already 
occupied by farms and large cattle ranchos. 
There are no rock formations that crop out along the trail; the whole substratum of the soil 
is loose drift, or sedimentary materials derived from the wearing down and disintegration of 
granite. At several places between the old ruins and the summit-level there are many rem¬ 
nants of a former extended slope, which once must have been united with those already described 
as flanking the base of the mountains at the Cajon Pass, and from which the present valley of 
San Bernardino has been excavated by the action of streams. The soil, formed by the minerals 
constituting the slope and the surface of the pass, is fertile and valuable for agriculture even at 
the summit. 
November 14.—The camp-ground was well shaded by numerous trees growing along the 
brook ; but a little further down the stream all the trees disappeared, and the water was fully 
exposed to the sun’s rays. As it was thought possible that there might be thermal springs on 
