Vol. XI] D1CKERSON—PT. REYES AND SANTA ROSA QUADRANGLES 533 



road. Three faults occupy the notches and the low ridges 

 are lowered but little if at all, below the former slope of the 

 mountain. (See Fig. 1, Plate XXXVII and Fig. 1, Plate 

 XXXVI and Fig. 1, Plate XXIX.) From these photographs 

 one might gain the impression that the drainage was toward 

 the observer along the Rift, but such is not the case entirely. 

 Only the lower portion of the valley is drained by the head- 

 waters of Rodgers Creek. In the upper portion of the rift 

 valley, the consequent streams still maintain courses across the 

 Rift. Rifting has affected some of their acute-angled tribu- 

 taries slightly by causing them to join their master streams 

 at right angles and made other minor deflections in their 

 courses. Rodgers Creek, however, drains the lower portion 

 of this rift valley and it has captured the upper portions of 

 the consequent streams which once drained across the rift. 

 This is evidenced by much interesting physiographic detail 

 on the southwest side of the rift in the region one to three 

 miles southeast of Petaluma reservoir. At a point a mile and 

 a quarter southeast of Petaluma reservoir, a wind gap of pro- 

 nounced character occurs and it is very evident that it was 

 once occupied by a consequent stream to the northeast which 

 is now tributary to the piratical Rodgers Creek. A mile 

 further on, another wind gap was found and in this case a small, 

 youthful tributary of Rodgers Creek is rapidly reversing the 

 drainage to the southwest. A considerable stream once occu- 

 pied this gap as its relatively wide valley in late maturity is 

 traceable a half mile west. In upper Rodgers Creek typical 

 fault sags are common and in the rift valley a mile and a 

 half southeast of Petaluma two or three elongate hills il- 

 lustrate the recent fault feature, the kernbut. Near the top 

 of the bordering southwest ridge, on the northeast side, a 

 narrow fault shelf was noted. Fault-sag ponds and kernbuts 

 are seen as one looks to the northwest from the north end of 

 Mountain School road toward Santa Rosa, and the rift evi- 

 dently extends in this direction along the southwestern face 

 of Bennett Mountain. This feature was not recognized 

 northwest of Santa Rosa unless the sharp line which separates 

 Santa Rosa Valley from the hills north of Santa Rosa town 

 represents a different expression of this line, similar to that 

 of the Hayward Fault, south of Hayward town. The pres- 

 ence of undrained fault-sag ponds, low side-hill fault shelves. 



