124 
GEOLOGY. 
the ridge hounding it on the lower side. This gives the basin the appearance of having been 
filled to the brim during a period of submergence. In most cases the drainage waters of these 
spaces find exit through a narrow gorge or ravine, at a point lower than the general level or 
crest of the ridge, and the basin appears but partly filled. Thus, about four miles from Yalle- 
cito, the trail passes over a narrow ridge of granite, which separates between two valleys or 
basins. The abrupt ascent from the lower valley to the crest of this ridge, where crossed by the 
trail, was much greater than the descent on the other side to the level of the upper valley; show¬ 
ing a considerable difference of altitude between the two. These high valleys between the ridges, 
filled with wash and soil, may be regarded as the reproduction, on a small scale, of a charac¬ 
teristic peculiarity of the Great Basin, which, as has been shown, is filled in some places nearly 
to the crest of the bounding ranges. 
The rocks between Vallecito and San Felipe, as seen akrng the trail, are mostly laminated 
and gneissoidal. About seven and a half miles from Yallecito, at the point where the frail 
makes an abrupt turn to the northeast, and winds in a narrow cut in the rocks, the laminated 
character is highly developed, and the laminae are much flexed and contorted. The general 
trend is N. 30° to 45° W.; and the notes upon the dip indicate a synclinal flexure of consid¬ 
erable extent, at that point. Compact granite, exposing a granular and friable surface, was 
also noted, and numerous feldspathic veins traverse the mass of rock. Many of these were of 
great magnitude, and consisted essentially of feldspar, associated with quartz and tourmaline. 
Several veins of this kind showed distinctly on the side of a ridge adjoining the trail; they 
were remarkably regular and parallel, and were from ten to twenty feet thick, dipping south¬ 
west at angles of about 45°. At San Felipe camp, the prolongation of one of these feldspathic 
veins forms the base of the ridge on the north, and contains black tourmalines of gigantic 
dimensions. Their crystallization is, however, so imperfect that no good cabinet specimens 
could be obtained. They, however, present some peculiarities of crystallization. 
No sedimentary rocks are visible between Yallecito and San Felipe ; the valleys are narrow, 
and bounded by rugged ridges of granitic rocks alone. There is but little vegetation between 
the two points ; the Agave and several varieties of cactus grow among the rocks, and several of 
the former were in flower. 
San Felipe .—The valley of San Felipe is more extensive than that at Yallecito. It is also at 
a much greater elevation, and is bounded on one side by the summit-ridge of the sierra. It is 
well supplied^with water by springs, and on the west side, by streams from the adjoining heights. 
Pine timber also grows on parts of the ridges towards the summit; in some of the sheltered 
ravines it is abundant, and of good size. Cotton-woods border one of the small streams for a 
short distance in the plain. The soil is good, and there is abundance of grass. 
The stream, which flows from the springs in the lower part of the valley, finds its passage 
through the mountain, outwards to the desert, in a narrow, rugged canon, on the north side, a 
little to the eastward of the Indian village. The rocks, as exposed along this natural section, 
consist of alternations of compact granite, with the laminated varieties. The trends are nearly 
north by the needle, and the planes of the beds or laminee nearly vertical. 
The rocks in the bed of the stream are partly covered by a remarkable incrustation, evidently 
deposited from the water. It was a foot thick in several places, and enclosed stems of reeds and 
small shells like those living in the brook. The occurrence of this calcareous crust on the rocks 
in a small brook, flowing towards the dry bed of the former lake, where such immense quantities 
of calcareous material once accumulated, is highly interesting. It, however, bears no resem- 
