574 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



of the Santa Rosa Quadrangle, as the anomalous dip of 10° 

 S. was recorded here. This, however, is local, as the beds 

 north and south of this locality exhibit little, if any, inclina- 

 tion. 



Within the northern extension of the Berkeley Hills block, 

 faulting, with possibly some folding incidental to it, has been 

 very vigorous in the northeastern portion of the Santa Rosa 

 Quadrangle during post-Pliocene time. The writer did not 

 have sufficient time to work out these structures in detail, 

 but certain broad features were recognized. Sonoma Moun- 

 tain for the major part has not been greatly disturbed by 

 faulting or folding except its northwestern extensions, Taylor 

 Mountain and Bennett Mountain. 



Kenwood Valley, a name which the writer proposes for a 

 northwest-southeast valley whose principal town is Kenwood, 

 appears to be a well marked graben, as the Mayacamas 

 Mountains rise abruptly from its northeastern border. These 

 mountains exhibit in some places exceedingly steep dips, as 

 high as 40° to 45° to the southwest. (See Fig. 2, Plate 

 XXV.) The peculiar courses of the streams draining this 

 valley are results of complicated fault movements in this vi- 

 cinity. Rincon Valley probably has a similar origin. The 

 hills north of Santa Rosa are in detail quite complicated by 

 folding and faulting. The Hayward fault, whose northern 

 extension is recognized on the northwest side of Sonoma 

 Mountain, is in this area as in its type locality, a very recent 

 feature, and it has not greatly modified the structure within 

 the Berkeley Hills block. 



During Epi-Miocene time the San Francisco-Marin Block 

 was upthrust, for an erosional surface was developed, upon 

 which the Merced was laid down. Possibly during the upper- 

 Miocene time this block was elevated also, since the Peta- 

 luma lake beds lying on the northeast side of Tolay fault 

 indicate that a land mass cut this region from the sea. Since 

 the Petaluma lake beds lie within the northern extension of 

 the Berkeley Hills Block, it appears probable that this block 

 was relatively depressed in upper-Miocene time. During 

 Merced-Pliocene time, the Point Reyes Triangle, an extension 

 of the Montara Block, and the San Francisco-Marin Block 

 were both depressed to receive marine Pliocene sediments and 



