32 SOUTHERN CALIFORNIA GEOLOGY 



ditions of the Pacific side are entirely different from 

 those of Southern California and especially from those 

 of the Los Angeles region (See Plates I and EC). It 

 is utterly unjust to classify them together. 



Examination of the earthquake map of California 

 by Dr. Willis shows that along a long and narrow coast 

 belt adjacent to the city of San Francisco^ there are 

 depicted no less than ten closely spaced parallel faults, 



'Notes on the structural geology of San Francisco (compiled). The Bay 

 of San Francisco is a submerged valley. If uplifted it would resemble Santa 

 Clara or Santa Rosa or Napa Valley. The present maximum depth of the 

 Golden Gates is 49 fathoms. The average depth of the bay proper is 4-8 

 fathoms. 



In the San Francisco area the general trends are northwest-southeast. 

 There are three orographic blocks : 



The Montava Block is on the west, through which pass the Pilarcitos and 

 San Andreas fault lines. This block is separated from the Marin-San Fran- 

 cisco block on the east by the San Bruno Fault. The Haywards and related 

 fault zone separates the Berkeley Hill block from the Marin-San Francisco 

 block. 



San Francisco-Martin and Montara Blocks have su.Tered recent depression 

 but the Berkeley block shows cut terraces with recent fossils — this is along 

 the margins of San Pablo Bay. Since Quaternary time the Marin peninsula 

 between Bolinas and San Francisco Bay has been depressed, thus allowing the 

 flooding of the lowered — net result being an uplift. Point Reyes peninsula has 

 been uplifted about 250 feet and then slightly depressed. San Francisco 

 peninsula shows slight subsidence. 



The main fault, San Andreas rift, is about eight miles from the city of 

 San Francisco proper. It passes to the west under the ocean. All the belt 

 of faults practically belong to the San Andreas zone. 



The San Bnino fault is about five miles southwest of the city. This line 

 of fracture is older than the San Andreas. It is paralleled on the northeast 

 by another fault zone which is nearer the city about half a mile. The San 

 Bruno fault joins the San Andreas near Bolinas Bay. The Haywards fault 

 is about eight miles to the northeast of this line, and there are many faults 

 both thrust and normal. 



The Haywards fault line is younger than the one along the base of the 

 Berkeley Hills along Which the original uplift took place. It may hold the 

 same relationship to this older fault that the San Andreas holds to the 

 San Binino. 



The San Andreas is a live fault. So far as it is notable in the area 

 the movement has been more horizontal than vertical. 



There are many minor faults in the San Francisco block, one of which 

 extends southeast through the city. There are several faults that cross the 

 main trend of the blocks. In the Berkeley Hills one passes down through 

 Strawberry Canyon (lying back of the campus.) Movement along this line 

 has placed the Quaternary beds against Cretaceous. 



The present population of the so-called metropolitan area lives around 

 San Francisco city and county, Oakland, Richmond, Berkeley, Alameda, and 

 parts of Contra Costa, Marin, and San Mateo counties which are adjacent. 

 The present metropolitan area might be said to include the district within 

 fifteen miles of the Ferry Building. The East-Bay region has fifty per cent 

 of the land area and forty per cent of the population. The metropolitan area 

 of the future it is said will cover a district within a forty-mile radius of 

 San Francisco. Insurance payments after the San Francisco fire were said 

 to equal $225,000,000. 



