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University of California. 



[Vol. 2. 



the western side of the peninsula all the shores are steep or precip- 

 itous. The cliffs bordering Drake's Bay have a nearly uniform 

 height of 200 feet. On both sides of the northern promontory 

 the cliffs range from 200 to 400 feet in height, and this continues 

 along a large part of the western shore of Tomales Bay. 



Submarine Topography. — Although there is nothing particularly 

 instructive in the submarine topography immediately bordering 

 the peninsula, yet this body being but a part of a crustal block 

 that is quite extensive it is not amiss to go a little beyond its 

 boundaries for information regarding its orographic history. The 

 maps of the Coast and Geodetic Survey furnish valuable data for 

 studying these problems. Westward from the peninsular border 

 the bottom of the sea slopes rather steeply for a mile or more 

 until a depth of nearly 200 feet is reached, beyond which line the 

 inclination is less than twenty feet per mile to the edge of the great 

 submarine bench, some twenty miles off shore, where the floor 

 plunges suddenly downward. Toward the south, between the 

 Farallone Islands and the mainland, the submarine terrace is still 

 better developed. 



Its average depth is about 200 feet. Although this portion of 

 the submarine terrace is opposite the Golden Gate, from which 

 issue the waters of the bay of San Francisco with all its drainage, 

 there is but little in its topography to indicate a great accumu- 

 lation of sediments from that source. When compared to the 

 adjoining portions of the terrace north and south, it is approxi- 

 mately a perfect continuation of the same level. A depression or 

 channel extends inwardly between the Farallones and Point Reyes 

 peninsula which possibly marks a former channel of the emboguing 

 river. Essentially this channel accords with the interpretation of 

 this submarine shelf, which regards it as an earlier terrace formed 

 when the land stood at a higher level. 



Drainage. — The drainage of the peninsula is in two opposite 

 directions and the features of its topography accord with those of 

 the general topographic development. The courses of all the 

 streams may readily be divided into three portions. There are 

 the ordinary steeper canons at the head, the stretch of narrow 

 gorge with a gentler slope, and lastly a usual stretch of a level 



