86 
GEOLOGY. 
formed ; the space thus partly enclosed is occupied by sedimentary formations. At the summit- 
level, the sediments which constitute the slope of the Great Basin form an almost vertical 
bluff, facing the south, and about 500 feet in height. It is necessary to descend this deep 
declivity in order to reach the valley of the little creek (Cajon creek) that flows to the valley of- 
San Bernardino. The descent of the pass is thus commenced at the very margin of the slope of 
the Basin, and there is no exposure of granitic rocks at the divide. The materials which com¬ 
pose this formation are rudely stratified, and many irregular beds of coarse gravel and granitic 
debris were noted. The lines of stratification, as seen in the face of the bluff, were nearly hori¬ 
zontal ; hut this exposure is believed to be at right angles to the direction of the dip, and there¬ 
fore does not give a correct view of the position of the strata. They probably dip northwards, 
or away from the granitic elevations, at a very slight angle ; no greater than their original 
position as deposited, and probably conforming very nearly to the present inclination of the 
slope. In their general appearance, the strata were like those seen at various places around the 
inner slope of the Bernardino Sierra, and they appear to consist, almost wholly, of the debris of 
granite, and to have been derived from the degradation of the surrounding heights, under the 
influence of currents or strongly agitated waters. 
Accumulations of this description have generally been termed drift or detritus in this report— 
these terms having been used in their most general sense, and without reference to the age of 
the formations. 
UPLIFTED SANDSTONE, CAJON PASS. 
Upraised sandstone strata .—A short distance below the bluff at the summit there are numerous 
low hills of regularly stratified sandstone. These strata are not horizontal, but are highly 
