Farallon 

 Islands 



Z. 



EXPLANATION 

 I | Quaternary rocks 

 I | Tertiary rocks 



Mesozoic rocks 

 I I Salinian terranes 



Franciscan terranes 

 I I Alcatraz Island terrane 

 1 I Coastal terrane 

 HI Marin Headlands terrane 

 j | Novato Quarry terrane 

 I I Nicasio Reservoir terrane 

 I I Permanente terrane 

 I i San Bruno Mountain terrane 

 i I Yolla Bolly terrane 

 I I Melange 



Great Valley Complex terranes 

 I I Gualala terrane 



Healdsburg terrane 

 Del Puerto terrane 

 I "': I Coast Range ophiolite 



Fault, dashed where 



approximately located 



Terrane map of the San Francisco Bay region. 

 Beneath the landscape of the bay region lie 

 fragments of at least 17 different bedrock types 

 that have been transported and juxtaposed by 

 movement along faults. The major basement 

 rock types can be ascribed to either the Fran- 

 ciscan terranes or the Salinian terranes. Rocks 

 west of the San Andreas Fault are generally part 

 of the Salinian terranes, whereas those east of 

 the San Andreas Fault are generally part of the 

 Franciscan terranes. These major terranes, sepa- 

 rated by the San Andreas Fault, are composed of 

 rock types that formed in very different geologic 

 environments and some of which were trans- 

 ported long distances by tectonic motion to their 

 present positions. 



14 Oceanography and Geology of the Gulf of the Farallones 



