448 University of California Puhlications in Geology [Vol. 12 



the direction 183°, and is certain. If, as Hayford and Baldwin^" are 

 inclined to think, "Sonoma Mountain did not moVe much, if any," 

 in 1906, then 1.24-|- meters is the measure of the strain creep in fifty 

 years, and the rate of strain creep is .025-)- meters per year. In the 

 absence of any determination of position between 1856 and 1906p 

 Sonoma Mountain is of interest chiefly in establishing the fact that, 

 if there were no sudden movement in 1906, then the direction of strain 

 creep was 183° ; and if a slight displacement did occur in 1906 the 

 direction of strain creep was somewhat more westerly than 183°. 



Fig. 6 ' Fig. 7 



Fig. 6. Chaparral moved 2.61 meters from A to D between 1856 and 1906 

 by strain creep, and 2.06 meters from D to C in 1906 by rebound. 



Fig. 7. Farallon moved 2.06 meters from A to D between 1860 and 1906 by 

 strain creej), and 1.29 meters from D to C in 1906 by rebound. 



Farallon. — Farallon Lighthouse is another important geodetic 

 station which was located by the surveys I, II, and III. It lies 

 37 kilometers to the southwest of the San Andreas fault in a direction 

 normal to its strike, and is the only station on the w'est side of the 

 fault for which we have measurements of displacements for all three 

 surveys. Fortunately these measurements are of a high order of 

 certainty. The displacements, whether those of slow strain creep or 

 of rebound, are remarkable for their large westerly component. The 

 positions of the station in the years 1860, 1891, and 1906p are indicated 

 by A, B, and C respectively in figure 7. The point moved 1.39 meters 

 in the direction 153° between the years 1860 and 1891. The direction 

 of the strain creep here is 20° more W'esterly than it is in the vicinity 

 of the San Andreas fault; but at a distance of 37 kilometers the 



10 Op. cit., p. 126. 



