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The National Geographic Magazine 



Tulare Lake and south of Red Bluff, near 

 the head of the Sacramento Valley. This 

 parallelism is not confined to the two 

 main ranges, the Great Valley and the 

 coast line, but is conspicuously shown 

 by the ridges and valleys of the Coast 

 Range. In the absence of local geolog- 

 ical knowledge, this feature of the topog- 

 raphy might be ascribed to regular fold- 

 ing, such as that of the Appalachians. 

 The actual complexity of the folding, 

 however, and the fact that the structural 

 details of the ridges show little accord 

 with the general topographic regularity 

 referred to, dispose effectually of this 

 suggestion. There can be little doubt 

 that the principal longitudinal ridges and 

 valleys of the Coast Range are due to 

 faulting modified by erosion. Much de- 

 tailed work remains to be done before 

 the positions and throws of all these 

 faults can be determined, but such care- 

 ful structural studies as have been made 

 of definite areas have invariably revealed 

 the great importance of dislocations hav- 

 ing a generally north-northwest trend. 

 This is particularly true of the San Fran- 

 cisco peninsula, which, as Prof. Lawson 

 has shown, is traversed by at least three 

 great faults belonging to this dominant 

 system. These have been plotted on the 

 accompanying outline map of the region 

 about San Francisco Bay and relief map 

 of the peninsula. The San Bruno fault 

 has a throw of at least 7,000 feet near 

 San Francisco, the southwest side having 

 dropped relative to the northeast side. In 

 all probability this same fault determines 

 the positions of Bolinas and Tomales 

 bays, north of the Golden Gate, and the 

 straightness of the coast line as far as 

 Point Arena, 100 miles northwest of San 

 Francisco. Toward the south the same 

 fault, or one belonging to the same zone, 

 is said to be traceable almost to the Gulf 

 of California, and in parts of southern 

 California is locally known as "the earth- 

 quake crack." The San Andreas fault, 

 which, as may be seen from the San 

 Mateo topographic atlas sheet of the 

 U. S. Geological Survey as well as from 

 the small relief map on page 287, is fol- 



lowed by a rectilinear ravine occupied by 

 a chain of ponds and lakelets whose ex- 

 istence is proof of recent disturbance. 

 The third, or Pilarcitos, fault has not im- 

 pressed its presence upon the topography 

 of the peninsula in as conspicuous a man- 

 ner as the other two. It is highly prob- 

 able that future careful work will dis- 

 cover other great faults generally parallel 

 with those mentioned. There is a strong 

 suggestion, for example, of a fault pass- 

 ing near San Jose, along the eastern 

 margin of the bay, through Santa Rosa, 

 and northwestward along the valley of 

 the Russian River past Ukiah. 



THE COAST IS STILL RISING 



There is still another series of move- 

 ments undergone by this remarkable 

 coast in late geological time, and these, 

 like the faulting, are still in progress. 

 Professor Lawson has clearly demon- 

 strated that the coast of California has 

 been elevated since the Pliocene to 

 heights ranging from 1,500 feet near San 

 Diego to over 2,000 feet in northern Cali- 

 fornia. This uplift is shown with great 

 clearness along the coast in the vicinity of 

 Los Angeles by conspicuous wave-cut 

 terraces, rising tier after tier above the 

 present strand and showing all the char- 

 acteristics of marine shores, even to pits 

 made by the same species of rock-boring 

 mullusc that inhabits the present beaches. 

 These movements have not been uniform 

 along the entire coast. For instance, the 

 mainland at San Pedro south of Los 

 Angeles has risen 1,240 feet, and San 

 Clemente Island, 50 miles farther south, 

 has risen 1,500 feet. Half way between 

 these two localities is Santa Catalina 

 Island, which not only shows no evidence 

 of recent elevation but is clearly under- 

 going submergence. One of the latest 

 phases of this vertical oscillation of the 

 shoreline has been the submergence of 

 the coast in the vicinity of San Francisco, 

 whereby the depression now occupied by 

 San Francisco Bay was transformed 

 from a valley to one of the finest harbors 

 in the world, and the Golden Gate, once 

 a river gorge, was prepared for the part 



