22 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
In the Coast Ranges between the Bay of Monterey and the Santa Barbara Channel, 
the chief valleys are those of Salinas River and its tributary, the San Juan; the Carissa 
_ Valley, and the valleys of the Cuyama and Santa Ynez Rivers. Of these the Salinas 
Valley is the largest. It is a wide, terraced valley cut by the river out of rather soft 
Tertiary and later deposits, which appear to have been in part let down against the 
older rocks of the Santa Lucia Range by the Santa Lucia fault. In its lower part it 
lies between the Gavilan and Santa Lucia Ranges, and the trend thus established is 
maintained by the main stream as far as San Miguel. Beyond that the same general 
trend is continued up its tributary, the San Juan, and thence thru the Carissa Plains to 
a point close to the southern end of the Great Valley. The eastern side of the upper end 
of the valley, particularly the eastern side of the Carissa Plains, follows closely the line 
of the modern earthquake rift to be presently described; and there can be little doubt, 
not only that in so far as the valley is an erosional feature its erosion has been controlled 
by structural features, but also that deformational processes have had a considerable 
share in its evolution. The axis of the valley thus indicated is singularly straight and 
has a length of about 175 miles. Its upper part, the Carissa Plains, is an arid plain with- 
out drainage and contains a very saline lake. This plain is a surface of alluviation. The ~ 
lower end of the valley opens widely on the Bay of Monterey and the fine stream terraces 
which flank its sides afford an excellent record of the recent uplift of the region. 
The valley affords another striking illustration of the obliquity of the geomorphic 
as well as the structural features to the general trend of the Coast Range belt, and their 
constant tendency to emerge upon the coast. From the eastern margin of the valley 
at the south end of the Carissa Plains, one can look down upon the Great Valley, near 
Sunset, a few miles distant; and only a narrow ridge separates the two valleys, altho 
they differ greatly in altitude. From this point in its course of 175 miles, Salinas Val- 
ley crosses the entire width of the Coast Ranges. South of San Miguel, the Salinas River 
proper lies in a less open valley with north and south trend as far as Templeton, a dis- 
tance of about 15 miles, and then opens out into a wider valley having a northwest- 
southeast trend for about 35 miles to the headwaters of the stream. Several of the minor 
tributaries of the Salinas show a marked tendency to the development of subsequent 
valleys. On the east side of the river, this is particularly marked on San Lorenzo Creek 
in Priest Valley, and on Chalome Creek in Chalome Valley. These comparatively large 
valleys may be referable in part, however, to deformation, inasmuch as they are 
on the line of the Rift. Their geomorphic history has not yet been studied. On 
the west side of Salinas Valley the two chief tributaries, the San Antonio and the 
Nacimiento, have developed well-defined subsequent valleys in the heart of the Santa 
Lucia Range. — 
In the valley of the Cuyama or Santa Maria River, the effect of a twofold structural 
control is apparent. The upper reaches of the river flow thru a broad valley with an 
alluviated bottom on the northeast side of the San Rafael Range. The general trend 
of the river in this part of its course is northwest-southeast, and it is separated from 
the Carissa Plains by a high mountain ridge with a very precipitous southwest front, 
which probably represents a fault-scarp. Below this expansive high valley, the stream 
enters a rather narrow canyon and shortly after this bends at right angles and flows 
southwest toward the coast, entering eventually on the broad Santa Maria Valley which 
is open to the sea. The contrast in the geomorphic character of the upper and lower 
reaches of the river, the greater age of the former, and the sudden change in the course 
of the stream where the two types of geomorphy meet, suggests that the high valley of 
the upper reaches was once connected with the Salinas drainage and that it has been 
captured from the latter, in comparatively recent time, by a stream cutting back from 
the coast at the northwest end of the San Rafael Range. 
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