TERTIARY STRATA——QUATERNARY GRAVELS. 37 
In the foot-hills of the same mountain, west of the river, the Tertiary rocks are very highly 
metamorphosed, and have been tossed about in great confusion. They consist of sandstones 
and shales, usually of deep blood-red color, with beds of conglomerate and white infusorial earth. 
They are broken through by masses of dark compact basalt, which has been poured over or 
forced between the strata, changing the protoxide of iron to the peroxide, and giving them, 
with their vivid colors, a considerable degree of hardness. The degree of metamorphosis which 
they exhibit is, however, generally so slight as to indicate that the beds of sand, clay, gravel, &c., 
were saturated, perhaps covered, with water at the time of the volcanic eruption. This is also 
indicated by the fact that the basalt, at the point of contact with the shale and sandstone, is 
converted into a highly cellular scoria, as though from steam driven out of the wet mass over 
which it was poured. 
I did not find the Tertiary strata, in any locality, extending more than a few hundred feet 
up the sides of the mountains. 
Fig. 9.—CLIFFS OF TERTIARY CONGLOMERATE, CAMP 54. 
Quaternary deposits.—Covering the Tertiary series, sometimes even to the height of three 
hundred feet above the river, are beds of gravel and sand; similar to those which border the 
Colorado below. These beds are in some localities partially consolidated, and when resting 
conformably on the older gravels it is impossible to draw a dividing line between them. The 
Same constituents form both series, and it is only where the influence of erupted masses is visible 
in the disturbance and consolidation of the older strata that they exhibit distinctive characters. 
We can only say, then, that at such a stage of the formation of the homogeneous, vertical column, 
volcanic eruptions occurred, by which the deposits already made were locally affected. 
In the trough which the Colorado has excavated in the Tertiary formation, the accumulations 
of more recent materials are, in many places, very conspicuous, even where they have suffered 
great degradation, still showing a stratified series, at least one hundred and fifty feet in thickness. 
