THE SAN ANDREAS RIFT AS A GEOMORPHIC FEATURE. 51 
somewhat contrasted geological provinces; one in which granitic rocks are extensive and 
important features, and the other in which granitic terranes are wanting. This fact 
further suggests that the two provinces will be found to be contrasted in other respects 
when the details of the Coast Range geology are better known. The general fact is indic- 
ative of relatively greater uplift on the southwest side of the Rift, and consequently 
deeper denudation, whereby the rocks of the granitic complex have been stript of their 
covering and so exposed to view. In that portion of the Coast Ranges south of the Bay 
of Monterey, the Santa Lucia Range along the coast is much higher than any of the other 
ranges which intervene between it and the great valley. 
In a discussion of the Rift as a geomorphic feature, it becomes a matter of interest to 
determine the relative importance of diastrophism and erosion in its evolution. There 
can be no doubt that where the Rift is coincident with pronounced longitudinal valleys, 
the latter, altho controlled as to orientation by the faulting along the Rift, owe their 
features in a large measure to erosion. ‘This is true, for example, of the valleys of the 
Garcia and Gualala Rivers and the San Andreas Valley. It is not so clear, however, as 
regards the depression between Point Reyes Peninsula and the mainland. It has been 
pointed out that in past geological time there has been a recurrence of faults with large 
vertical displacement on this portion of the Rift, dating back to pre-Miocene time and 
possibly to the Cretaceous; and it may be that here the depression is essentially dias- 
trophic in origin and only modified to a minor degree by erosion; similarly with some of 
the valleys along the Rift, and extending from it in the Southern Coast Ranges. The 
Cholame Valley and the valley of Carissa Plain may be essentially diastrophic in origin, 
modified by erosional degradation on their sides and by aggradation of their bottoms. 
The depressions which constitute the Rift along the southern margin of Mojave Desert 
appear to be practically wholly diastrophic, altho somewhat aggraded. Where the Rift 
hugs the steep northeast flank-of the Santa Cruz Range as far as Wright Station, and the 
similarly steep southwest flank of the same range from Wright to Chittenden, it is difficult 
to avoid the conclusion that these steep mountain flanks are in reality degraded fault- 
scarps, and are, therefore, the walls proper of a great asymmetric Rift valley. The same 
conclusion applies to the steep north flank of the San Rafael and San Gabriel Ranges, on 
the south side of Mojave Desert. The complete discrimination of effects of diastrophism 
and erosion in the larger features of the relief associated with the Rift will require many 
years of patient field work. 
With regard to the minor features which characterize the Rift in detail, thruout its 
extent, the discrimination is less difficult chiefly because the diastrophic effects are of 
comparatively recent date and their distinctive features are not yet obliterated by the 
ravages of erosion. These consist chiefly of scarps, low ridges, and sinks or ponds. 
In many cases it is apparent that both erosion and aggradation are controlled by these 
minor features, and that the latter tend to become obliterated. These minor scarps, 
ridges, and sinks are not referable to any single earth-movement, but are referable to 
a recurrence of movement on the same general line. In the southern Coast Ranges the 
observations of Fairbanks show that one of these movements was of exceptional impor- 
tance. By it displacements and disturbances of the surface were effected which dwarf 
all similar events in historic times. For miles at a stretch the earth, upon one side or 
the other of the fault line, sank, giving rise to basins and to cliffs 300 to 400 feet high. 
These features, in the opinion of Fairbanks, who personally examined them, were the 
result of one movement. This displacement probably occurred not less than 1,000 years 
ago. It is certainly older than the great trees growing upon the ridges and hollows 
formed by it. Since then it is probable that numerous displacements of less extent have 
taken place, but the geomorphic effects of the smaller movements have, in some consider- 
able measure, been effaced. Since the settlement of the state, the strain in the earth’s 
