62 
GEOLOGY. 
reason to doubt that the outcrops are the prolongation of the metamorphic rocks in the lower 
parts of the pass. At that place the trend was nearly east and west, and the dip to the north, 
at an angle of 70°. Here we find, first, a northerly dip of 30° to 40° ; and again, further west, 
a tread of N. 70° E., with a southerly dip of 75°. The dips are thus reversed, and a great 
flexure of the beds, with the greatest dip towards the south, is indicated. Lieutenant William¬ 
son ascended to the top of the mountain, and states that the rock is mica-slate, similar to the 
lower portions I examined. 
October 17.—We left the Cow camp, and once more journeyed with the wagons, travelling 
eastward along the valley. This is hounded by the low sedimentary hills on the north, hut 
soon opens out upon the broad slope of the Great Basin. The sandstone hills disappear in a 
point; and at this place I was able to make an observation upon the position of the strata, 
which, before that time, had been so much concealed by their own debris and soil that no satis¬ 
factory results could he obtained, although I was disposed to regard them as horizontal. These 
strata were thickly bedded, and consisted of the debris of granite and pebbles of dark porphyritic 
rocks. They are not horizontal, but dip northwards, at an angle of 75°. Their trend was 
N. 85° W. It is probable that this is only a local uplift, and that the hills further west are 
composed of horizontal strata. 
About six miles from the Cow camp we found the commencement of a broad area of low and 
rounded hills, of sedimentary formations, which are in all probability the extension of the same 
deposits found throughout the valleys we have been travelling in since leaving Lake Elizabeth 
and the Pass of San Francisquito. This is also the vicinity of the entrance to' a new pass dis¬ 
covered by Lieutenant Williamson during our stay at the last camp. The sedimentary hills 
rise above the general slope of the Basin, and extend for two or three miles or more opposite the 
pass, appearing to fill out a bend or depression in the mountains. At the western side of this 
body of hills, the strata of one of the ridges are distinctly inclined about 25°, and consist of 
alternations of white, red, and greenish clays. The white consists chiefly of decomposing 
granitic sand. There are no hard rocks in these hills ; all the strata are soft, and can be easily 
cut through. They are bare of trees, and had a barren, forbidding aspect. They much 
resembled the tertiary hills of Ocoya creek. 
Our course lay around the base of these hills at the north, and thus was out upon the 
broad slope of the Great Basin. Before passing, however, to a notice of the phenomena 
observed there, a retrospective glance should be given to the peculiar and fertile character of the 
strip of country at the base of the north side of the main chain of the Bernardino Sierra. This 
fertile strip consists of the chain of longitudinal valleys connecting by their ends, formed by 
outlying low ridges, either of granite or sedimentary hills, at a short distance from the main 
ridges of the Sierra. Nearly all these valleys, extending over a distance of more than forty 
miles, or from the center of the Canada de las Uvas to Williamson’s Pass, are adapted to culti¬ 
vation. Grass grows luxuriantly in most of them, and the soil is deep and rich. There is no 
lack of water, which, though not found in running streams of any size, is abundantly furnished 
by springs and ponds. It is very probable that the temperature of these high valleys is low 
during the winter, and that considerable snow accumulates in them. While we were encamped 
at different points, ice nearly half an inch thick was several times formed. 
About fifteen miles beyond the entrance to Williamson’s Pass, we travelled over low hills, 
composed of sand and gravel and the debris of granite and metamorphic rocks. Descending a 
narrow valley among these hills, where there was a great quantity of sage bush of unusual size, 
