1921] Lawson: The Mobility of the Coast Ranges of California 447 



represent the positions of this station in 1856, 1891, and lOOG;?. In 

 the interval from 1856 to 1891 the point moved 1.83 metei's in the 

 direction 173°. This is at the rate of .052 meters per year, practically 

 identical with the rate for Tamalpais. Again there is no reason to 

 suppose that the movement stopped abruptly at B in 1891. It doubt- 

 less continued in the same direction at the same rate till 1906a, when 

 the strain generated reached the limit. Applying the rate of strain 

 creep to the interval 1891-1906, we find that the station must have 

 moved an additional .780 meters and reached the position D. On 

 April 18, 1906, the station moved back by the rebound to C, a distance 

 of 2.06 meters in the direction 337°. 



But again, as in the ease of Tamalpais, the path of the station in 

 its rebound from D must have been parallel to the near-by San Andreas 

 fault, the azimuth of which is indicated in the diagram by the line hh' ; 

 and by rebound from D along the line hh' the station could never have 

 arrived at C. The same two possible explanations obtain here a.s in 

 the ease of Tamalpais. As Chaparral moved northerly under strain 

 creep the near-by San Andreas fault must have moved in the same 

 direction at the same rate, keeping a constant azimuth. If aa' be the 

 position of a line parallel to the fault in 1854 it would have moved to 

 bV in 1906a; and at the time of the earthquake it might have sprung 

 back to the position cc', either by a slip on a deep fault, or by a 

 transfer of strain to the southwest side of the fault. Failing this the 

 only other available explanation is that C was located about a meter 

 too far south by reason of the assumption of immobility of the 

 Diablo-Mocho base. Whichever explanation be the true one, the 

 apparent transverse shift measured normal to the fault is here .57 

 meters. 



Ross Mountain. — Ross Mountain was similarly located by the sur- 

 veys I, II, and III, and a similar analysis and interpretation may be 

 made of its movements from 1856 to 1906p. The rate of strain creep 

 here was .053 meters per year and its direction was 182° ; but as the 

 station is relatively remote from the San Andreas fault, the measure of 

 the rebound, in this case a doubtful figure, was only somewhat more 

 than half that of Tamalpais and Chaparral. The apparent transverse 

 shift measured normal to the azimuth of the San Andreas fault is 

 .35 meters. 



Sonoma. — Sonoma, 34 km. distant from the San Andreas fault, to 

 the east, was located in 1856 and again in 1906p, but not in the interval 

 between. The displacement between these dates was 1.24-|- meters in 



