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CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



wind gaps of small order and minor stream modifications all 

 indicate movements along this line within the last 200 years 

 as many such transient topographic features would have been 

 obliterated within a longer time. No fault furrows or recent 

 fault scars which might be the surface results of movements 

 along this line on April 18, 1906, were found, but the great 

 destruction in the town of Santa Rosa on that fateful day 

 may have been due to subterranean movements along this 

 northern extension of the Hayward Rift. 



The physiography of the San Francisco-Marin Block is 

 intimately tied, both to the geologic history of this region 

 previous to the Pleistocene and that very changeful period 

 of the Pleistocene itself. A study of the peculiar type of 

 stream drainage within this block has given the essential 

 clews to the history of this region. Professor Holway's 32 

 paper upon the Russian River described the Russian 

 River and its tributaries on this block, and his paper upon 

 the Physiographically unfinished Entrances to San Francisco 

 Bay 33 describes the peculiar drainage of Walker Creek and 

 San Antonio Creek, and that of Elk Creek in Sausalito and 

 Tiburon peninsulas. Professor Holway brings out some in- 

 teresting topographic facts concerning Liberty Gap, which is 

 a few miles northwest of Petaluma, and shows that a general 

 coast depression of 250 feet would cause the sea to invade 

 the Santa Rosa Valley from the west. In this paper he de- 

 scribes the valley of Walker-San Antonio Creek under the 

 name of Lagoon Pass, and indicates that it would be flooded 

 with a similar depression. 



The writer will not describe the details of the drainage 

 in this block, as much would be merely a repetition of Pro- 

 fessor Holway's excellent work, but will confine his discussion 

 to such additional bits of information derived from a study 

 of this region from a slightly different point of view. The 

 streams draining into Tomales Bay and the Pacific Ocean 

 have certain characteristics in common. From Russian River 

 these streams are, in order, Salmon Creek, Estero Americano, 

 Estero San Antonio, Lagunitas Creek, and one of the small, 

 but interesting streams of the Tamalpais region, Elk Creek. 

 All these streams were flooded a greater or lesser distance 



-Univ. Calif. Publ. Geog., Vol. 1, No. 1, 1913. 

 33 Univ. Calif. Publ., Geog., Vol. 1, No. 3, 1914. 



