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University of California. 



[Vol. i. 



will be found in the remnants of old baselevels which are traceable 

 from the San Francisco Peninsula on the flanks of Montara Moun- 

 tain southward to the Santa Cruz Range. If now we could obtain 

 data for the measure of the tilting- in a direction normal to the coast, 

 it would be possible to locate the major and minor axes of the curve 

 corresponding to the periphery of the sunken area, if the latter be 

 not complicated by faulting. On this point we are not entirely 

 without suggestion. The uplifted coastal peneplain is clearly dis- 

 cernible on the east side of the Bay of San PYancisco as a dissected 

 plateau represented by longitudinal and transverse ridges. These 

 ridges, when viewed from a suitable standpoint, such as the upper 

 flanks of Grizzly Peak, at Berkeley, fall into a slope, whose average 

 maximum elevation is about 1,500 feet. The meridianal profile of 

 this dissected plateau presents no marked sag. Its east and west 

 profile, on the other hand, shows a decided slope towards the Bay of 

 San Francisco. The presumption is, therefore, that the longer axis 

 of the sunken area is parallel with the coast. The same conclusion 

 is supported by the evidence from the Farallone Ridge, which 

 appears as a series of islets running parallel with the coast about 21 

 miles out to sea, off the Golden Gate. A low terrace on the east side 

 of San Pablo Bay (Bay of San Francisco ) and at the Straits of Car- 

 quinez indicates an uplift at that locality which is subsequent to the 

 subsidence. Its distribution is not yet known. 



The subsidence 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 a fact, it is difficult to conceive the Sacramento River 

 having an)' other relation to the Coast Ranges which it traverses 

 than that of an antecedent stream. The Pliocene rocks around the 

 Bay of San Francisco and Mount Diablo establish the presence of 

 a marine Pliocene basin over this portion of the Coast Ranges. 

 The late Tertiary rocks of northern Marin County in the vicinity 

 of Tomales and Freestone may belong to the same basin. These 

 Pliocene rocks were all affected by sharp orogenic deformation prior 

 to the general uplift of the coast. It is improbable that the Sacra- 

 mento drainage across the Coast Ranges antedates this movement. 

 Put, once established, it probably persisted throughout the whole 



