56 
GEOLOGICAL REPORT-THIRTY-FIFTH PARALLEL. 
their nearly flat roofs, and for making pavements. In a ravine near one of the springs I found 
the exposed edges of bituminous shales, they being brownislr-black, and in some places the 
bitumen was visible. 
Intrusive trappean rocks .—On the road from San Bernardino to Los Angeles, and not far 
from Cahuenga rancho, there are several hills of moderate elevation, not over 100 or 150 feet, 
and one of them is composed of a hard trappean rock. It may form a part of a range of hills 
believed to extend nearly northwest and southeast, between the valley of San Bernardino and 
the sea. 
Alluvial valleys .—The whole slope, from the mountains to the ocean, may be said to be fertile 
and susceptible of cultivation wherever water can be obtained. The valleys of the streams are, 
however, peculiarly favorable for cultivation, and the bottom lands can hardly be surpassed for 
their fertility. 
