176 CARNEGIE INSTITUTION OF WASHINGTON. 



1. Study of Geological Formation along the California Fault-Lines. 



This problem has received consideration, both before and since the 

 great San Francisco earthquake in 1906, but for various reasons our 

 knowledge is still inadequate in the fault zones. It will be most effec- 

 tively performed by the United States Geological Survey with the co- 

 operation of the Departments of Geology at the California universities. 

 The plan should include a detailed map of the line of the San Andreas 

 rift with measured displacements, as well as special geologic examina- 

 tions and maps of other significant localities. 



In carrying out this plan the attempt should be made to determine 

 not only the surface formations in which effects of displacement are 

 visible but, in so far as there are available exposures, to ascertain the 

 character of the formations at considerable depths. The recent field 

 observations undertaken by the Geological Department of Stanford 

 University will contribute to this latter purpose, and it is understood 

 that these studies will be continued as opportunity may offer. 



2. Surface Displacements. 



Following the great San Francisco earthquake in 1906, the United 

 States Coast and Geodetic Survey reoccupied its earlier stations in the 

 vicinity of the San Andreas fault and determined, by reference to the 

 Mocho-Diablo base-line, a number of displacements on both sides of 

 the rift. No determination was made of the stability of the base-line 

 itself, although it lies within the zone of movement. 



More recently, both the Ukiah and Lick Observatories have reported 

 indications of a northward drift of those stations. The order of magni- 

 tude of this drift as reported by Ukiah amounts to 0.3 meter per year. 

 The latitude of Mount Hamilton as determined from meridian-circle 

 observations for the accurate positions of stars showed a northerly 

 drift in the period 1893-1915, but with a strong set-back at about the 

 time of the severe earthquake of August 3, 1903. The Mocho-Diablo 

 line lies substantially between these two stations. 



It should also be noted in this connection that the observations of the 

 Coast and Geodetic Survey made in 1907 establish positions as of the 

 period immediately following the earthquake, i. e., after the accumu- 

 lated strains which may have caused the slip had been released. 

 Similarly, the earlier triangulation measurements were affected in a 

 manner not now determinable, by the earthquake of 1868. It is very 

 likely, therefore, that the comparative measurements of record, thus 

 far, yield incomplete information concerning either the direction or mag- 

 nitude of crustal strains to which these slips were due, although the 

 magnitude of the slips themselves has been measured in several localities. 



In the opinion of the Committee, therefore, it is a matter of con- 

 siderable importance to invite the United States Coast and Geodetic 

 Survey to continue these measurements and, if practicable, to extend 

 them before another considerable slip occurs. It is also of the first 



