UPRAISED STRATA—-AURIFEROUS SLATES. 59 
These strata consist of alternations of conglomerates, sandstone, and shales, in beds of 
variable thickness and order of succession. The color varies from gray to buff-yellow, and 
further south to red. The strata are in a semi-consolidated state, and wear away rapidly by 
the action of the weather. Beds of hard sandstone were, however, seen, and may, perhaps, be 
found in all of the outcrops. These outcrops of sandstone were found on both sides of the trail 
for about two miles, and the formation appears to extend northeasterly in a narrow valley between 
the granite or metamorphic rocks and a ridge of talcose and micaceous slates rising south of 
them. 
The extent of this valley, and its position relatively to the pass, will be seen on the small 
map of the region, (Map IL.) The outcrops are also represented on the general section of the 
Bernardino Sierra, which extends through this pass. 
No intruded rocks in the form of dykes or otherwise were found among these upraised strata, 
although careful search along the line of exploration was made. As the strata rest immediately 
upon the adjacent granite, it at first appears that their disturbance and flexed condition was 
produced by its intrusion. I looked in vain for an exposure of the line of junction between the 
two formations, neither could I detect any great metamorphism of the sediments, which would 
probably have resulted if they had been upraised by the inruption of the contiguous granite. 
It is, therefore, probable that the disturbance was produced by some igneous intrusion at a dis- 
tance, and not visible along the line of observation. This intrusion may have displaced a 
portion of the granite together with the strata. Further explorations must determine to what 
agency these strata owe their present position, whether to a granitic intrusion between them 
and the Great Basin, or to the inruption of dykes of porphyry, or the approximation of the 
ridges of granitic and talcose rocks, between which the flexures are the most bold. 
Lower down the creek, in the vicinity of the ridge of talcose slates, (see section,) the sand- 
stone formations on the right bank are not so much tilted and bent as higher up in the pass; 
consequently they do not form such abrupt and precipitous hills. The valleys become more 
broad, and in some places the strata are nearly horizontal. A large quantity of oxide of iron 
also enters into their composition, and imparts a red color to some of the beds, 
Age of the sandstone strata.— With regard to the age of these strata, I am unable to affirm 
positively, but am disposed to regard them as Tertiary. Not a single fossil was found in all the 
outcrops, and therefore there is no such evidence of their age. Their resemblance to the strata 
at the southern end of the Tulare valley was noted; yet they do not show such a great thick- 
ness, nor such thick and firmly consolidated beds. 
Ridge of talcose and auriferous slates.—The first distinct outcrop of the talcose and gold-bear- 
ing rocks met with south of the Mariposa district is exposed in this pass about nine miles from 
- thesummit. Atthis point the brook issues from among the hills of sandstone, and impinges 
upon a slate ridge, and afterwards follows the dividing line between it and the sandstones for a 
long distance. 
These slates form a distinct ridge of several hundred feet in elevation above the bed of the 
cañon, trending nearly due east and west, (magnetic, and they can be seen to extend in an 
unbroken ridge for several miles eastward. A narrow valley is thus formed between them and 
the granite, which is partly occupied by the outcrops of tilted sandstone just described. The 
dip of the slate is at an angle of 70° northwards, and is very regular and uniform. The rock 
differs somewhat from those generally described as talcose, found in the auriferous region of the 
Atlantic States, and also from those seen in Mariposa county. The color is dark gray, passing 
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