6 
GEOLOGICAL REPORT-THIRTY-FIFTH PARALLEL. 
is broken at intervals by passes. The peak is regarded as between eight and nine thousand feet 
high ; and being the highest point in that region, it was deemed appropriate to extend the 
name to the chain of which it forms such a prominent and well known feature. 
The average elevation of the Bernardino Sierra may be regarded as 6,000 feet. The Cajon 
Pass, through which the exploration was made, lias, according to the observations, an altitude of 
4,689 feet; and according to those made by Lieutenant Williamson, in the month of November 
preceding, is 4,676 feet. The adjoining ridges on the west are probably 2,000 to 2,500 feet 
higher. The ascent from the Mojave river to the pass is very gradual and uniform, and pre¬ 
sents a great contrast with the descent towards the Pacific, which is abrupt and short. On the 
G-reat Basin side, the gradual slope of the surface reaches to the very summit of the pass ; while 
on the other, the upper edge of the gradual slope is 3,000 feet below it. From the western base 
of this chain, the line of the survey and the profile passes over a gently descending slope to the 
Pacific ocean, and there are no intervening ridges of any great magnitude. 
Mogoyon Sierra .—This chain, although not traversed by the expedition, is nevertheless so 
near, and holds such an important relation to the line, that it is necessary to present a brief 
notice of it in connexion with those just described. After passing the Sierra Madre, the Sierra 
Mogoyon, or Sierra Blanca, were seen at the south, trending apparently a few degrees north of 
west and south of east. They were, to all appearance, continuous to a point nearly south of 
San Francisco volcano. Several streams take their rise in the range, and flow northward to the 
Colorado Chiquito. Mr. Marcou mentions this range particularly in his notes, and in his 
Resume. The strata appeared to flank these mountains, and to dip away from them towards the 
north. According to the same authority, the direction of the range is u east east-south and 
west west-north.” The apparent direction or trend is very different from that of the ranges 
crossed by the survey, and is similarly opposed to the direction of the mountain ranges south of 
them. This fact renders it somewhat questionable, whether the nearly east and west direction 
which was observed is not more apparent than real. The plotted notes and bearings to this 
range indicate that its direction is not so nearly east and west as was supposed, and show that 
the elevation probably extends northward as far as the volcano of San Francisco, which would 
thus appear to rise upon a continuation of the same elevated swell of the surface. The few 
notes and observations, also, go to show that the elevation at the volcano is formed, not by a 
ridge or line of sharp erupted rock, but by a swell of the underlying strata, producing an elevated 
table-land similar to that of the Aztec mountains. 
This character of the surface is shown by the topography on Lieutenant Whipple’s map. It 
will also be seen, by inspecting that map, that the Mogoyon mountains appear to extend in a 
curvilinear line southeasterly from the San Francisco volcano, and that the southeastern 
portion attains a nearly due east and west direction. The explorations a short distance south 
of this part of the range, on the Gila river, show that there the prevailing direction of the mount¬ 
ains is northwest and southeast. It is possible that this part of the chain consists of many par¬ 
allel and short ranges, trending northwest and southeast, and which, by overlapping one beyond 
the other, produce the continuous appearance. This peculiarity is well seen in the Great Basin 
and along the eastern border of the Colorado desert, where isolated ridges seem to form con¬ 
tinuous ranges. The direction which is apparent in this range is, however, very nearly that 
of the Bernardino Sierra, and the two chains are nearly upon the same parallel of latitude. 
The almost rectangular intersection of the Bernardino Sierra with other chains should prepare 
us for similar phenomena in other localities. I am, however, of the opinion that future 
exploration will show the composite character of the Mogoyon Sierra, and that it is formed hy 
a series of ranges trending northwest and southeast, conformably to most of the ranges of that 
region. 
San Francisco Volcano .—The description of this great elevation was not given in its geograph¬ 
ical order among the mountain chains, as it is considered probable that it forms a local uplift, 
rather than a linear elevation. In the description of the Mogoyon Sierra we have seen that 
