2132 The American Geologist. October, i8tt7 
along this part of the coast and it is impossible to believe 
that any structural conditions alfecting the soi't Pliocene and 
Pleistocene deposits could have formed a valley of this kind, 
and there can be no other explanation but that of a compar- 
ativel_y recent subsidence. 
North of San Pedro hill near Redotido there is a long, deep 
and narrow valley extending up very near to the shore. An- 
other valley but not so narrow occurs off Santa Monica. The 
Redondo valley extends easterly toward the very northern 
portion of San Pedro hill which accordiiig to Lawson consists 
at the base of Miocene shale dipping westward at an angle 
not to exceed 30 degrees. Tlie northern and eastern sides of 
the hill consist of more recent formations. As the submarine 
valley extends east and west it is consequently not at all like- 
ly that it is of structural origin. Lying to the east back of 
both valleys is the broad Los Angeles plain of Pliocene and 
Pleistocene strata. It appears to extend beneath the sea form- 
ing a broad even slope down to the 100 fathom line. 
The next broad land valley to the north is that of the San- 
ta Clara river, which flows across Ventura county, with a gen- 
eral east and west course though bending toward the south 
near its mouth. Opposite nearly the middle of the broad al- 
luvial bottom of this valley, though some miles south of the 
present mouth of the river, is another submarine valle}^ reach- 
ing a depth of 300 fathoms and extending'up very closely to 
the shore. Its direction is the same as that of the land valley 
on which it opens. As is the case with most of the submarine 
valleys this one is narrow and deep, and the question arises 
why is this so when the corresponding land valleys are oft-en 
as in the present instance miles in width. If due to subaerial 
erosion their upper portions at least must have been cut out 
of the Pliocene deposits which filled the post-Miocene erosion 
valleys. Their narrow deep form woiild indicate that the 
post-Pliocene elevation was of a comparatively brief duration. 
About six miles to the south of the valley described, and 
nearly opposite the present mouth of the Arroyo Las Posas, is 
another submarine valley of about the same size as the last 
and extending more nearly north and south. It reaches to a 
little greater depth than the last, but also extends up close to 
the shore, terminating near the west end of the lagoon at 
