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

SLOPE BORDERING THE MOUNTAINS-RAVINES IN THE CLAY.
mountains, which was composed of gravel and boulders. Portions of it were undoubtedly of
recent formation, and had been spread out by heavy floods from the canons of the mountains.
There were, however, large areas of surface that were evidently in the same condition as when
left by the water of the former lake. On these portions, rounded boulders and large masses of
rock were so thickly spread that the wagons could not pass over them. These were all incrusted on the upper or exposed portions with a dark-brown crust, evidently very different
from the white variety that incrusted the shores. Some parts of this crust was of a dark-red
color, and very hard. I turned over many of the rocks, and found that generally the incrustation did not extend T)elow the surface of the gravel and clay in which they were imbedded. I
was evidently standing on the bottom of the old lake and but little or no change had taken
place since the waters had retired. From the appearance of this slope, and the rocky character
of the bottom, and the absence of the fine blue clay that forms the greater part of the surface
of the old lake-bed, I was led to believe that strong currents from the adjoining mountains and
carons had entered the old lake near this point.
Ravines in the Clay.-The rugged and rocky character of the higher parts of this slope made
it necessary to descend with the wagons to the more level and hard surface of the clay. Here,
other impediments to our progress constantly occurred. The rains or floods from the mountains, in traversing the surface, had cut deep ravines, which extended for miles directly across
our course. These were about as deep as their width, and their sides were vertical. They
resembled great fissures rather than valleys of excavation. In some places they were so
narrow that it seemed almost possible to jump from one side to the other, and yet they were
from twenty to thirty feet deep.
These singular cuts in the clay are formed at numerous points along the slope from the
mountains. Many of the ravines commence and attain their greatest depth within a distance
of three or four hundred yards. Their upper portions consist of multitudes of diverging channels, spreading out like the branches of a tree. The water collected by these branches becomes
concentrated in the principal ravine, and after flowing for a short distance it passes out upon a
lower part of the slope, and again diverges into small channels. This was the general character
of the ravines that we crossed, and several of them were miles in length, and so deep as to be
impassable except at their upper and lower ends, where the depth is not great. It is probable
that these deep cuts in the clay are formed by a sudden flood of water from the mountains, or
perhaps, by unusual rains during the winter. We lost much time and expended much labor
on these ravines; it was necessary to find a place where the wagons could be taken down into
them, and then to find a convenient point at which to construct a road to draw them out on the
other side. The bed of a small tributary, or side fissure, was generally selected, and leveled by
shovels so that the mules could be driven up and down.
The vertical walls of these ravines were of fine clay in horizontal strata, sometimes mingled
with sand, and varying in color from a grayish-blue to a light reds; one or two layers of coarser
materials, pebbles, &c.,X were observed in the upper parts of some of the sections, but may have
been laid down by surface floods since the lake was drained. Multitudes of small spiral shells,
like those found near Deep Well, were also visible, imbedded in the strata: but no specimens of
Planorbis were seen.
We travelled among these ravines until after midnight, and the men and animals being
exhausted, we lay down on the hard clay to sleep until daylight.
November 19.-Daylight showed that we had nearly reached the point of the mountains
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