The San Francisco call. [volume] (San Francisco [Calif.]) 1895-1913, 1895-10-06


! subsequent tributary of that river. Here
| the subsistence seems to have reached it's
| climax, for to the southwark the flooding
of valleys gradually becomes less promi.
nent, and cannot be said to be in evidence
much south of the latitude of the southern
end of the bay of San Francisco. Not only
does the subsistence appear to eliminate
| at the Golden Gate, but In the depth of the
| water in that passage we have very proba-
| bly, the measure of maximum subsistence
"Generally the delta accumulation of the
| Sacramento River and other streams has
kept pace with the submergence of the
| valley, and the greater part of the bay of
| San Francisco is very shallow. In con-
stricted places, however, where the cur
rents are swift, the sediment has not &C.
| cumulated to the same extent. The great
| volume of water flowing in powerful cur
rents through the Golden Gate with every
| incoming and outgoing tide has been more
effective for the transport OF sediment than
anywhere in the bay or out beyond the
heads, and, as a consequence, we have here
! the deepest water. The maximum depth
of the Golden Gate is 378 feet at it's mar
rowest part, and if we assume this to rep
resent the depth of the bedrock of the
submerged Sacramento River we have
| direct measure of subsistence. Within the
bay of San Francisco the deepest water is
in the Raccoon Straits, where the lead
shows thirty-nine fathoms, or 234 feet of
water. This passage appears to be the
| landward prolongation of the Golden Gate,
and may, with great probability be ac-
cepted as portion OF the ancient river
trench.
"The region around the bay of San Fran
cisco abounds in minor but very significant
evidences of submergence. A view of the
bay in clear weather from the university
buildings looking toward San Rafael is an
| ideal picture of sunken tract, the islands
of the bay being very clearly the SUBMITS
and crests of billy portion of the former
valley. Richardson's Bay is clearly a
flooded valley. The various marshy en-
payments of the shore between Tiburon
Point and the Carqulnez Straits are also
flooded valleys, which have become more
or less completely silted up to the level of
high tide. Outside of the entrance to the
Golden Gate there is evidence of a similar
order. Rodeo Lagoon is an incipient
ford, flooded only in its lower portion.
Lake MERGED is a flooded stream valley.
the bottom of which is ten feet below the
tide. Halfmoon Bay belongs to the same
category of things.
1.-THE subsistence which allowed the sea
to invade the land through the Golden
Gate seems to have been the first event of
this kind since the general post pliocene
uplift of the coast was inaugurated. If this
be fact, it is difficult to conceive the Sac
ramento River having any other relation
to the Coast Ranges which it traverses
than that of an antecedent stream. The
pliocene rocks around the bay of San Fran
cisco and Mount Diable establish the pres
ence of marine pliocene basin over this
portion of the Coast Ranges. These plio-
Gene rocks were all affected by sharp
local reformation prior to the general up
lift of the coast. 1t is improbable that the
Sacramento drainage across the Coast
Ranges antedates this movement. But once
established it probably persisted through
out the whole subsequent uplift of the
coast, sinking its trench as the uplift pro-
ceeded.
Associated with the subsistence which
flooded the bay of San Francisco there
were probably other determinations of the
crust which seem to have had an important
influence on the drainage. The most
notable instance of this kind is the shift
ing of the divides of the photographic
basin of the Russian River. This stream
once clearly flowed down through Peta-
luna Valley to the main drainage outlet
at the Golden Gate. A low divide in the
middle of the old valley now causes the
drainage to flow westward at right angles
to its former southerly course, and seek
the coast by its present transverse route.
The change in the drainage may be due to
stream capture or to crystal warping. The
latter is most probably the cause but the
problem has not yet been studied suth-
GENTLY.
1.-THE most remarkable development of
pliocene rocks in North America is on the
peninsula of San Francisco q few miles
south of the Golden Gate. The remark
able features are: a. The great thick
ness of continuous sedimentation which
it represents and % the local disturbance
to which it has been subjected. Both of
these features are observable and qnan-
titatively determinable in the magnificent
line of seachff which extends from Lake
MERGED, near San Francisco, to Mussel
Rock, about eight miles south of Point
Lobos, at the entrance to the gate.
''The base of the pliocene rocks here re-
ferred to as the MERGED series is observable
at MusseI Rock. The basal bed is
stratum of partially carbonized forest
material from which fragments of little
altered wood, bark, branches, matted
leaves and fine cones may be gathered ad
libitum.
THE cones, according to Professor E. l..
Greene, are those of the Monterey pine, a
tree which, at the present time, grows only
at Monterey. The forest bed rests upon
seemingly even surface of volcanic rocks
which are of mesoZoic age. In a small
canyon about half way between Mussel
Rock and Twelye-mile House, section of
these MERGED beds may be observed at
about, probably, the middle of the series,
in which trunks OF trees are imbedded,
which project out from the vertical banks
into the canyon. With these trees are as
sociated cones which are those of the
Douglass spruce. The timber of these trees
is well preserved, and, as erosion exposes
the trunks, the people of the neighboring
ranch cut them into firewood. In a vertical
section above this pliocene kindling are
marine shells of species which have been
identified.
1.-The fact of finding fossiIiferous plio-
Gene strata at elevations of over 700 feet is,
of course, absolute demonstration of an
elevation of the coast to that extent in
t-pliocene time. This itself might,
however, be due to the general uplift which
has affected the entire coast. The general
uplift is but factor in the total effect of
the movements which have been active on
the San Francisco peninsula in post-plio-
Gene time. The occurrence of volume OF
pliocene strata over one mile thick, in
clined at high angles (up to IS deg.) is
absolute demonstration of the very i'm
portant differential movements of local
character. The base of this great volume
of strata exposed above sea at the same
Level as the summit of the series, with so
small horizontal interval between sum-
nit and base, tells Us in language more
forcible than words, the measure of this
Qifferential movement The pre-nliOcana