1921] Laimon: The Blohility of the Coast Ranges of California 445 



region on both sides of the San Andreas fault, and are not necessarily 

 synchronous with the movements on that fault. As will appear from 

 the discussion which follows, the earthquake of 1868 was probably due 

 to sudden relief of the longitudinal strain in the region south of the 

 Golden Gate, on a low dipping, deep fault, the emergence of which at 

 the surface has not yet been observed. 



EEGION NOETH OF THE GOLDEN GATE 



I shall now review briefly the data for various geodetic stations 

 the positions of which were determined at various dates, and interpret 

 those data in the light of the elastic rebound theory. 



a' 



Eig. 5. Mount Tamalpais moved 3.04 meters from ^ to D between 1854 and 

 1906 by strain creep, and 1.97 meters from D to C in 1906 by rebound. 



Tamal/pais. — We may take first the case of Mount Tamalpais. The 

 positions of this point were determined by surveys I, II, and III. In 

 figure 5, let A, B, C represent the positions in 1854, 1882, and 1906 

 respectively. Between 1854 and 1882, a period of twenty-eight years, 

 the point migrated 1.64 meters presumably in a straight line, the 

 azimuth of which is 168°. There is no reason to suppose that the 

 movement ceased abruptly in 1882 ; and we may safely assume that it 

 continued at the same rate in the same direction up to 1906a,° as the 

 manifestation of the accumulating strain which was relieved in that 

 year at the time of the earthquake. The rate of strain creep from 



9 Throughout this paper 1906a means 1906 prior to the earthquake and 1906p 

 means 1906 after the earthquake. Similarly 1868a and 1868p mean 1868 before 

 and after the earthquake respectively. 



