454 University of California PuMications in Geology ["Vol. 12 



agrees with the creep inferred from the displacement between surveys 

 I and II for the controlling stations, Tamalpais, Chaparral, and Ross 

 Mountain ; whereas if the apparent shift is due to a migration of the 

 primary base the values for the creep thus independently arrived at 

 do not agree. 



Fort Ross Group. — The Fort Ross group of geodetic stations may 

 also be reviewed to advantage in the light of the elastic rebound theory. 

 There are twelve stations in this group, five on the east side and seven 

 on the west of the San Andreas fault. The data necessary for their 

 discussion are tabulated below : 



station 



Date 

 of 



Survey II 



Distance 

 from fault 

 Km. 



Displacement 

 between surveys 

 II and III 

 Meters 



Direction 

 of 



displacement 



Funcke 



1891 



0.4 W 



2.33 



139° 



Pinnacle Eock 



1891 



1.6 W 



2.47 



158° 



Fort Boss 



1891 



1.9 W 



2.50 



147° 



Timber Cove 



1891 



1.9 W 



2.22 



144° 



Stockhoif 



1891 



2.6 W 



1.78 



144° 



Horseshoe 



1891 



2.9 W 



1.48 



137° 



Salt Point 



1891 



3.2 W 



2.01 



138° 



Henry Hill 



1891 



1.5 E 



1.46 



320° 



Dixon 



1891 



1.8 B 



1.37 



316° 



Chaparral 



1891 



1.8 E 



1.34 



328° 



Peaked Hill 



1891 



2.0 E 



1.2,7 



301° 



Lancaster 



1891 



2.0 E 



1.77 



327° 



Azimuth 



of the fault 141°. 









In addition to the determinations above listed Chaparral was also 

 located in 1856. In 1891 it was found to have moved 1.83 meters in 

 the direction 173°, that is in a period of thirty-five years, or at the 

 rate of .052 meters per year. This movement was doubtless shared by 

 all the stations in this group. Of the seven stations to the west of the 

 fault Pinnacle Rock is anomalous in the direction of its displacement 

 between surveys II and III ; but the other six are fairly consistent 

 both as to direction and amount. The average of these six stations, 

 2.05 meters in the direction 141°, is therefore taken as a better expres- 

 sion of the absolute displacement than the average of all seven. Of 

 the five stations on the east side Peaked Hill is anomalous in direction, 

 while the other four are consistent. The average of these four stations, 

 1.48 meters in the direction 323°, is therefore taken as a better expres- 

 sion of the displacement than the average of all five. With these mean 

 values we may construct a diagram illustrating the movements of the 

 ground. In figure 9 let A be the position in 1891 of a small circle 

 bisected by the San Andreas fault, aa', and B the point to which it 



