1921] Laivson: The Mobility of the Coast Ranges of California 463 



fault, an apparent transverse shift whereby the fault was moved 

 parallel to itself to the southwest. I shall, therefore, allow for this 

 and assume that the station in 1906a was on the circle aa' at D, a 

 little to the east of the point of intersection of the line cC. Then the 

 line DB is the azimuth of strain creep, and this is 163°. The exact 

 position of D is uncertain, but its departure from c is doubtless a 

 small quantity, and the position assigned to it will serve my present 

 purpose, which is not to arrive at exact numerical expressions for the 

 various displacements, but to develop a consistent hypothesis as to the 



Fig. 12 Fig. 13 



Fig. 12. The path of Bed Hill as determined by strain creep and the 

 rebounds of 1868 and 1906. 



Fig. 13. The path of Loma Prieta as determined by strain creep and the 

 rebounds of 1868 and 1906. 



general path of a station between 1854 and 1906p in the disturbed 

 region south of the Golden Gate. But if BD be the direction of strain 

 creep then the path of the station from 1854 to 1868a must have been 

 on the same azimuth. It is fair to assume, therefore, that in this 

 interval of fourteen years the station moved .085 X 14 = .812 meters 

 in the direction of 163°. Thus we have the position of the station 

 just prior to the sudden movement of 1868, at E. Similarly after the 

 earthquake of 1868, the station moved from F to B, .98 meters in the 

 direction 163°, so that the position of the station immediately after 

 the sudden movement of 1868 is also known. The line EF gives 

 therefore, both the amount and the direction of that sudden movement, 

 which was 1.68 meters in the direction 321°. Thus, by way of sum- 

 mary, the path of the geodetic station Red Hill between 1854 and 

 1906p was from A to E by slow strain creep, from E to F by sudden 

 rebound in 1868, from 7'^ to D by renewal of strain creep, and from 

 D to C by sudden rebound in 1906. The last movement from D to C 



