i9o6T A hong Fault 



the original break dating from the mountain-making 

 periods of Miocene and Pliocene times. 



The San Andreas fault' which determines the 

 axis of Tomales Bay (north of San Francisco) and in 

 which the catastrophe of 1906 took place is doubtless 

 part of a very lengthy ancient break probably ex- 

 tending through Bering Sea on the north to Pata- 

 gonia on the south.2 Our particular disturbance Frorn 

 visibly concerned only a stretch of 192 miles in a ^^''^°<^''^° 

 straight line (mainly on land) running from the %!nZ 

 mouth of Alder Creek in Mendocino County to 

 San Juan Bautista in San Benito. 

 _ As a natural phenomenon it decreased progressively 

 in violence from Mendocino down. Beyond San Juan 

 Its effects could be traced by the fall of chimneys as 

 far as Priest Valley, forty miles to the south; and the 

 town clock at San Bernardino, on the same line but 

 400 miles farther on, is said to have stopped at just 

 thirteen minutes after five on the morning in ques- 

 tion. The great earthquake of 1868 was caused by a Rijtof 

 rift which extended from above San Francisco still '^^^ 

 farther southward through the Carisa Desert in San 

 Luis Obispo County to the mountains of Los Pinos in 

 Ventura County. The ancient break, however, really 

 runs by way of Cajon Pass, San Bernardino, San 

 Jacinto, and Imperial Valley, to and through the 

 Gulf of California. 



^ In the San Andreas fauh — as probably in all 

 similar breaks — hundreds of thousands of earth- 

 quakes, large and small, have taken place in geologic 



1 First traced and studied (so far as I know) by Dr. Branner in the 'go's. 

 . buch, at least, is the view maintained by Dr. F. Omori, a distinguished 

 seismologist of Japan, who came to California immediately after the earthquake 

 and who regards the great temhloT in Chile which followed on August 17 as 

 occurring in the same rift. ' 



C 181 3 



