Vol. XI] DICKERSON-PT. REYES AND SANTA ROSA QUADRANGLES 581 



Creek, Carriger Creek and other small streams are tributary 

 to the master stream, Sonoma Creek, which drains into San 

 Pablo Bay. Roger's Creek is another one of these streams, 

 but through the aid of the Hayward Rift it has succeeded in 

 capturing a portion of the drainage of the southwest side 

 of Sonoma Mountain. The southwest side of Sonoma Moun- 

 tain is drained in part by Tolay Creek and Petaluma Creek 

 into San Pablo Bay, while the northwestern half of this 

 drainage has an indefinite water parting on the fan of Cope- 

 land Creek at Cotati divide. The waters of Copeland Creek 

 and Crane Creek now find their way into Laguna de Santa 

 Rosa, a stream on the western side of Santa Rosa Valley. 



Hayward Rift 



The northwestern extension of the Hayward Rift is easily 

 recognized on the southwestern slope of Sonoma Mountain, 

 where many characteristic features are seen. The general di- 

 rection of the rift is, through most of this area, about N. 4U 

 W in the Santa Rosa Quadrangle, but its general trend as it 

 crosses the northeastern corner of the Petaluma Quadrangle 

 is about N. 20° W. Like the Hayward rift in the Berkeley 

 Hills, this rift is not a simple fault line, but a series of 

 parallel fault lines in a zone which varies from a quarter to 

 a half mile in width. Lawson 29 has shown that the Hayward 

 Rift in the Berkeley Hills is a very recent feature which has 

 only modified the original consequent drainage of the south- 

 western slope of the Berkeley Hills in a minor way. The 

 same condition is essentially true along the extension of this 

 line in the Petaluma and Santa Rosa Quadrangles. One 

 mile east of the Eureka School on the Sonoma-Petaluma 

 Road three beautiful fault sag ponds were first recognized 

 alon- a half mile strip in a direction N. 20° W., and the 

 corresponding small blocks which were separated from one 

 another by interspaces, which, like the fault sag ponds, are 

 due to a series of minor differentially dropped blocks. The 

 hills and their interspaces are bounded on their northeast and 

 southwest sides by faults of the Hayward Rift Zone. Such 

 a series of differentially dropped blocks are termed by Law- 



- Lawson, A. C. San Francisco Folio, No. 193. U. S. Geological Survey, p. 17, 

 1914. 



