TERTIARY STRATA OF CARRIZO CREEK. 
121 
the lagoon and the mountains, I observed the edges of argillaceous strata in thin, slaty beds. 
These were soft, and not unlike those seen north of Salt creek in November. Still higher up the 
slope, and before the hill at the valley of the creek was reached, another outcrop was found. This 
was, however, composed of sindstone ; the strata dipping westwardly, and showing thick beds. 
They did not stand out much above the surface, and were much obscured by a wash of gravel 
and sand. They were light-colored and probably Tertiary. 
The approach to Carrizo creek over the long and gradual slope affords a good view of 
the mountains which bound the Desert on the west, and separate it from the coast slopes near 
San Diego. These mountains are the continuation of the same ranges which were constantly 
seen on the right hand during the passage of the Desert southwards from the San Bernardino 
Pass, and are portions of the great chain extending throughout the peninsula of California. 
The ridges at Carrizo creek are peculiarly barren and forbidding in their appearance, and, 
being without soil, are exceedingly rough and rugged. 
Mountains of this character border both sides of the valley of Carrizo creek, but do not reach, 
the vicinity of the road, so that they could not be readily examined. They, however, appeared 
to be composed of granitic and gneissose rocks, similar to those found in the ridges further 
north. Some of the ridges were very dark-colored, or nearly black, and may be erupted rocks, 
more recent than the gneiss. 
The hill, at the upper edge of the slope by which the valley of the creek is reached, has 
already been noticed. When standing on this hill, and looking westward between the ranges 
of mountains, it becomes evident that the wide valley is occupied by nearly horizontal sedimen¬ 
tary strata, through which the creek has cut its way. It has excavated a wide and deep chan¬ 
nel, cutting away and carrying out upon the margin of the Desert a large portion of the mate¬ 
rials that once filled the valley to a much higher level than the present bed of the creek. This 
denuding action has left vertical walls at various places on each side of the stream, in which the 
horizontal layers of the sediments are exposed ; and wherever side streams have entered the 
valley, other channels are formed, and isolated hills, with flat tops, are left standing, as if to 
indicate the former level of the surface. The exposed edges of the strata, so well seen in the 
natural sections, were not all horizontal, but presented various degrees of inclination and direc¬ 
tion of dip. This, of course, would result where slightly inclined strata are cut in different 
directions by the tortuous course of a stream. From the repeated observations of the dip, and 
their relation to the configuration of the valley, I was led to conclude that their general or pre¬ 
vailing direction was from the granite ranges oh each side towards the centre of the valley. No 
inclination greater than 20° was observed. There were, however, indications of comparatively 
local disturbances in the lower part of the valley, near to the slope of the Desert, in which the 
FAULTS IN SANDSTONE STRATA, CARRIZO CREEK. 
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inclinations were much greater. These were seen from a distance, on the south of the trail, and 
were not far from a ridge of dark-colored rocks, which, from its appearance, I suspected might 
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