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.
valleys, or ravines, formed in this deposit by the little streams entering from the north, are, in
several instances, terraced on both sides. Between stations sixty-two and one hundred and six,
a ravine is very distinctly terraced, and is rendered more interesting by a deposit of rounded
and angular masses of rock, from one to two feet or more in diameter, on each bank just at the
margin of the terrace. These rocks are so thickly spread that the soil is invisible in some places,
and in others, they are within stepping distance of each other. In width, this belt or margin of
erratics is not over thirty or forty feet, and is generally more narrow. It is singular that they
are found at the margins of the terraces only. It is possible that they are of glacial origin, but
may have been washed out of the banks by the stream, when of greater volume than now, and
accumulated along its bed, to be afterwards cut through by a more narrow and a deeper channel,
and thus left, in part, on each side. Under this supposition, that the stream, producing the
eroVion, has gradually been diminishing in volume, the terraced form may be explained without
resorting to the hypothesis of a sudden uplift of the region.
Local deposits of large blocks of granite are found at several places on the plain-like surface
of the Tejon, between the site of the Depot Camp and the entrance to the Pass. This granite
corresponds, lithologically, with the granite found in the Pass and in the upper portions of
Tejon Ravine. The blocks have evidently been transported from the valley of the Pass or the
ravine. They do not border the bed of any stream, but extend in long lines on the surface.
Similar accumulations are, however, found along the course of the creek, after it flows from the
ravine of the Pass. If the other accumulations were originally deposited along a creek, all
traces of its bed are removed. Some of the blocks along the creek are over fifteen feet in diameter,
and it seems hardly possible that they could have been rolled forward from their source even by
a great flood. It is possible that they were transported by glaciers at some remote period when
the climate may have been favorable for the formation of such bodies of ice.
The granitic and metamorphic rocks on the Great Basin side of the mountains pass beneath
nearly horizontal strata, which are probably Tertiary. These strata are overlaid by a thick accumulation of more recently deposited materials —the wash and detritus from the ridges. It could
not be determined whether the edges of the strata, which were obscurely exposed in the sides of
the valley, were, in reality, very different from, or older than, the materials of the slope. They
are, however, believed to be of the age of the Tertiary, and to extend beneath the superficial
deposits of the Basin in the same manner as on the west side. Similar strata pass below the
Surface deposits of the Tulare plains. The probability that they are Tertiary is increased by the
occurrence of sandstones believed to be of that period on r the corresponding slope of the ada
de las Uvas twenty miles further south.
SECTION AT TIlE CANADA DE LAS UVAS.
By referring to the Geological Map, it will be seen that the Pass, called the Cainada de las
Uvas, is situated about twenty miles southwest of the Tejon Pass, and leads from the southern
end of the Tulare Valley to the Great Basin. It may be said to turn the southern extremity of
the Sierra Nevada, although the mountains are of equal altitude beyond. The break in the
mountains is much greater than at the Tejon Pass, and the narrow canon, or the rocky portion
of the valley of the Pass is much shorter, and is near to the entrance from the Tejon or Tulare
slope. Beyond this, the Pass is a succession of open, elevated valleys between ridges. This
configuration of the Pass is -not so favorable to observations on the granitic rocks, and they were
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