GEOLOGY OF THE COAST SYSTEM OF MOUNTAINS. 15 
tectonic lines of the Coast System to the general trend of the coast has long been familiar 
to California geologists and has been particularly noted by Fairbanks,’ but the probable 
explanation of it has not heretofore been set forth. 
The coastal scarp is interrupted at a number of points and in a variety of ways. The 
most notable and interesting interruption is that of the Bay of Monterey. This is not 
only an embayment of the coast, but is a depression in the Coast Ranges extending down 
over their submarine portion to the 12,000-foot contour below sea-level. It brings the 
3,000-foot submarine contour well inside the general line of the coast. This submarine 
valley has been regarded by some writers as a submerged valley of subaerial erosion, 
but there is little warrant for this view and much that conflicts with it. The valley of 
the Bay of Monterey, subaerial and submarine, is a synclinal trough the axis of which 
is approximately normal to the trend of the coast and of the Coast Ranges as a belt. 
In the axis of the syncline, and probably parallel to it, is a fault seen in the canyon 
between Pajaro and Chittenden, which brings down the Tertiary rocks on the north side 
against the pre-Cretaceous granitic rocks of the Gavilan Range. Another interruption 
of the continuity of the coastal scarp is at the Golden Gate. Here the Coast Ranges have 
been locally deprest and the land valleys which were formerly drained by a trunk stream, 
where the Golden Gate now is, have been flooded by the waters of the ocean. The axis 
of this depression is, however, not well known. A third, apparent rather than real, 
interruption of the coastal scarp occurs at the place where the Point Reyes Peninsula 
projects out beyond the general line of the coast. Inside of the peninsula, however, there 
is a long narrow valley, the northern end of which is occupied by Tomales Bay and the 
southern end by Bolinas Lagoon, which separates it from the mainland proper; and to 
the east of this valley the coastal scarp rises with exceptional boldness. 
The coastal scarp has had its profile modified in many places by wave-cut terraces 
formed during the uplift of the coast by stages in Pleistocene time, as previously stated. 
The relation of the coastal scarp to deformed basins of Merced (late Pliocene) strata 
indicate that it originated, in its essential features, at the period of orogenic activity 
which brought the Tertiary to a close. South of Point Conception the twofold system of 
faults which determines the configuration of the coast gives out and we enter upon a 
region of probably more complicated structure. The Santa Barbara channel appears to 
he in a geosynclinal trough between the Santa Ynez range and the island chain from Ana- 
capa to San Miguel. On the northeast side of San Clemente is a sharply defined fault- 
scarp, indicating that the island is a portion of an uplifted and tilted orographic block. 
The fault along which the scarp has been formed probably extends as far as the east 
side of Santa Barbara Island. San Clemente Island presents a magnificent series of 
wave-cut terraces up to an elevation of 1,500 feet. San Pedro Head is similarly uplifted 
and terraced, while the intervening island, Santa Catalina, shows no evidence of corre- 
sponding uplift, but has on the contrary been deprest. On the whole, the channel 
island platform between the edge of the subcontinental shelf and the coast presents the 
characters of a sunken mountainous tract, the inequalities of the surface of which are 
partly due to acute deformation and partly to erosional sculpture when the region was 
above sea-level. A more detailed interpretation of the structure of this region is ren- 
dered difficult by the absence of adequate soundings of the sea-bottom. 
Granitic Rocks. — Coming now to the consideration of the more important structural 
features of the Coast System, in the territory between the coast and its eastern mar- 
gin, it must be stated that even here our information is very scant. One of the most 
important features of the Coast System from a structural point of view is the occurrence 
of a belt of granitic rock having a very notable linear extent thruout the ranges. This 
granite, as has been already stated, appears, in the vicinity of Tejon Pass, both from 

1 Am. Geologist, Vol. x1, Feb. 1893, p. 70. 
