THE EARTHQUAKE RIFT OF 1906 305 



clear. It may be that this is part of the Pajaro cross-fault. The 

 original Portola-Tomales fault, if continued in a straight line from 

 Chittenden, would pass along the flanks or the foot of the Gavilan 

 mountains to Priest Valley, fifty miles to the south-southeast. Beyond 

 Priest Valley is a well-marked earthquake crack, which opened in the 

 earthquake of 1868, and in earlier times. This extends through desert 

 land in the same direction, its course being the axis of the Cholame 

 Valley and the uninhabited desert sink known as Carisa Plain. This 

 old rift extends at least one hundred and forty miles beyond Chittenden 

 to Monte Pinos in the north edge of Ventura County. This whole 

 fault from Point Arena to Monte Pinos is clearly a single break, but 

 only 192 miles of a possible 330 were opened in the earthquake of 1906. 



But while the surface break seemed to end at Chittenden, it seems 

 probable that the rift in the rocks below extended much farther. At 

 Priest Valley, fifty miles along this line, the shock was violent, while 

 at localities ten miles or more to the east and west of the line, as at 

 Lone Oak or the Pinnacles, it was very little felt. In Priest Valley 

 chimneys and shelving were thrown down, buildings badly shaken and 

 the contents of a country store impartially scattered over the floor, the 

 shock being apparently about as severe as in San Francisco. 



With the opening of the great rift it is conceivable that faults in 

 the neighborhood should also be affected. There is evidence (most of 

 which the writer has not examined) of the opening of a parallel fault 

 behind Cape Mendocino. This seems to have passed across the base 

 of the cape, cutting across the smaller headland called Point Delgada, 

 losing itself in the Sonoma Valley to the southwest of Santa Eosa. 

 There are distinct traces of it across Burbank's famous orchard at 

 Sebastopol. Here on a slope lines of fruit trees were shifted, a well 

 was moved bodily three or four feet, and a crack about one fourth mile 

 long extended across a neighboring field, its direction parallel with 

 that of the Tomales rift. Other similar cracks open at intervals on the 

 road toward Point Delgada. The extreme violence of the shock in 

 Santa Eosa perhaps indicates its nearness to this second rift, as the 

 Tomales rift caused little damage in other towns equally far away. 

 Dr. G. K. Gilbert takes a somewhat different view of this case. He 

 seems to regard this Point Delgada crack as part of the great Tomales- 

 Portola rift. In his map (Popular Science Monthly, August) Dr. 

 Gilbert marks the great rift as swinging eastward in a curve across 

 Point Delgada and to the eastward of Cape Mendocino between that 

 headland and Humboldt Bay. It seems to the present writer far more 

 probable that the Point Delgada fault is a separate rift, parallel with 

 the main rift, and similar to it, except that it is a little less violent. 

 There is some evidence that a fault line at the foot of San Francisco 



VOL. LXIX. — 20. 



