Reports of explorations and surveys, to ascertain the most practicable and economical route for a railroad from the Mississippi River to the Pacific Ocean: Vol. 5, Pt. 2

SAN GORGONO-METAMORPHIC ROCKS.
following the shallow bed of a brook in which water was flowing rapidly, but without trees or
much vegetation on its banks. It appeared as if it had been entirely dry for the greater part
of the summer. On reaching the next extended spur of San Gorgono, we encamped on the
eastern or lower side, in order to avoid the strong wind which continued to blow without cessation. A considerable quantity of sand was found here also, and on the lee side of the rocks.
The point was long and low, and the rocks were perfectly bare and very much broken. It was
composed of a succession of granitic, gneissose and slaty rocks, intercalated with limestone and
quartz rock, similar to those before described. The trend of. the planes of structure was found
to be the same, (N.W. and S. E.,) dip N. E., about 40~. The peculiar laminated structure,
and constant alternation of gneiss and mica slate, with narrow layers of limestone, was well
shown. All these layers were much contorted and bent, and were traversed by numerous feldspathic veins. An extended sketch-section was made of this point of rocks, and a portion of it
is presented here, and will serve to indicate the characteristics of the rock.
SECTION ON THE EAST SIDE OF SAN GORGONO.
s I # s # I I s
1, 1, 1, limestone; g, g, granite, or feldspathic veins; s, s, s, gneiss, mica slate and granite.
The limestone formed lenticular beds, from one to eight or ten feet in thickness, conformable
with the slaty rock, and partaking of its flexures and contortions. The slight thickness of these
beds, and their lenticular form, led me to regard some of them, at least, as segregations. There
was not time before dark to make measurements of the breadth of the different layers of rock,
and indeed it would scarcely be possible to do it, -as the variations between the compact and
granitic portions, and the gneiss and finely laminated mica slates, were very gradual, and no
distinct lines of demarcation could be found.
The stream of water flowed at the base of the rocks in a shallow bed of sand and gravel, and
not a tree or blade of grass was visible on its banks. A short distance below, it spread out
over the gravelly surface, and became completely absorbed by the sand. Our camp was near
the piles of drifted sand, and the wind continued to blow through the night, and brought with
it the grains of sand, making a rustling sound as they poured over the rocks and settled in all
the hollows and crevices which the wind could not reach.
We had travelled twenty-two miles from the summit, and were nearly at the base of the pass,
or at about the same elevation as the valley of the Santa Anna river at San Bernardino.
November 15.-The aspect of the country around the camp was peculiarly dreary and desertlike; towards the east and southeast a broad plain extended, and was bounded in the distance
by brown and barren-looking mountains. They are represented in the engraving, but appear
too near, and the plain too narrow. Grass and vegetation among the rocks, and clouds in the
sky, have also been added by mistake. It is seldom that an artist is called upon to picture a
scene so barren and desolate. The timber upon the mountains gradually disappears after passing
the summit of the pass, and none is found on the eastern or inland side. Huge specimens of
the melo-cactus were, however, abundant among the rocks.
We travelled southeasterly over the now broad and plain-like slope of the pass, and continued
to descend. Several, spurs of San Gorg()no were passed in succession; they extend out for a
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