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

GEOLOGY.
seen at the summit, continues to extend on the left, and by its decomposition furnishes an
excellent soil. We crossed many small streams, which furnish abundance of water to all parts
of the valley, and permit the luxuriant growth of grass and oak trees. All the hills along the
road were green with oaks' and chamizal, delighting the eye with their verdure after the
pilgrimage on the Desert.
Santa Isabel is a beautiful valley among the mountains, well watered, and bordered by groves
of oak and other timber. It has a varied and undulating surface, and a good granitic soil.
Adobe buildings of great size were erected here in the time of the Padres, but are now partly in
ruins. They were, however, in part, occupied as dwelling and storehouses, the valley being
used as a cattle rancho. The surrounding hills were but sparsely wooded, but were covered
with dried grass, showing the presence of a deep soil and abundant verdure during the spring
and early summer.
December 18.-Santa IsTabel to San Pasqual, 23.5 miles.-Gray, compact granite, similar to
that at Agua Caliente, was found in the vicinity of Santa Isabel. About seven miles beyond, it
became more syenitic in its character, and the surfaces that had been exposed to weathering, and
to decomposition in the soil, exhibited small, brilliant crystals of green hornblende, standing
out in relief, having resisted decomposition better than the feldspar, in which they were imbedded. Several miles beyond this point, on the side of the hill, the soil is colored red by a
large amount of peroxide of iron, probably derived from the decomposition of pyrites. Fragments of quartz veins were also abundant. Large veins of feldspar and quartz were numerous
along the road, and could be traced on the slopes of several ridges in the vicinity. Their white
color showed distinctly through the green shrubscovering the hill-sides, and there appeared to
be several nearly parallel veins. The first of these that was observed had a trend nearly northwest and southeast, magnetic. It appeared to be principally composed of coarsely crystalline
feldspar, quartz, and tourmaline, with garnets, similar to the vein found on the other side of
the divide at San Felipe. The feldspar in this vein, however, was more highly crystalline and
good crystals can be obtained there. The tourmaline, by its decomposition and abrasion, furnishes a large amount of black sand, which is distributed along the beds of the brooks and
rivulets of the vicinity.
Just before reaching the lagoon, the direction of the veins was found to be more nearly east
and west, several of them having a trend of only five degrees north and west, magnetic.
Observation of the trend of the granite at that point gave the same result. These quartzveins
and the red soil so highly charged with iron were regarded as indicating the presence of gold,
but no examination or "prospect" could be made for it. We travelled very rapidly, and there
was little opportunity for examination of the rocks beyond the trail.
After winding about the hills by a very crooked road, we reached the Rancho of Santa Maria,
a fine open valley or plain, with good grass and water.
The observations made, under date of December 16, respecting the elevated valleys of the
eastern slope of the mountains, will apply to this, the western side, also. The true character
of the descent is not so distinctly visible as where the rocks and surface are almost entirely free
from vegetation; but still it is evident, in descending towards the Pacific, that you pass successively from a high plain to a low one by a sudden descent, showing the existence of stair-like
elevations or terraces, very different from the character of the slopes of the Sierra Nevada.
I Leaves of a species of oak growing most abundantly along the valley were collected, and have been submitted to Dr.
Torrey. He regards the oak as very near Q. intbricaria of the Atlantic States.
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