I-AU'SON.J 



Coast of Northern California. 



265 



has been cut down through a terrace of the immediately preceding 

 uplift. 



At the Golden Gate we have the flooded trench of the most 

 important river on the California!! coast. The southern part of the 

 Bay of San Francisco is the flooded valley of a subsequent tributary 

 of that river. The structure which controlled the erosion was for the 

 most part established by the post-Pliocene orogenic disturbances 

 which deformed the Merced Series. That orogenic deformation 

 was not the immediate cause of the flooding of San Francisco Bay, 

 as might be inferred from a statement of the writer in a former 

 paper.* The orogenic movement there referred to simply estab- 

 lished structural conditions which controlled the erosion of the 

 valley, that at a much later period was flooded by the sea. The 

 full extent of this subsidence was not appreciated by the writer at 

 the time the paper referred to was written, and, although the Bay of 

 San Francisco was recognized as a sunken tract, it was not then 

 clear that the subsidence was entirely subsequent to the general 

 uplift of the coast. The limitation of the discussion to the features 

 south of the Golden Gate, which was imposed upon the writer in 

 the former paper by his lack of familiarity with the country to the 

 north of that point, precluded his entering upon the question of the 

 origin of the Bay of San Francisco. 



At the Golden Gate the subsidence seems to have reached its 

 climax, for to the southward the flooding of valleys gradually 

 becomes less prominent, and cannot be said to be in evidence much 

 south of the latitude of the southern end of the Bay of San Fran- 

 cisco. The bedrock of the valley is exposed at Coyote, 63 miles 

 by rail from San Francisco, at an elevation of 250 feet above sea. 

 Not only does the subsidence appear to culminate at the Golden 

 Gate, but in the depth of the water in that passage we have, very 

 probably, the measure of maximum subsidence. 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 constricted places, 

 however, where the currents are swift, the sediment has not accu- 



"This Bulletin, Vol. 1, No. 4, p. 159. 



