72 



University of California. 



[Vol.*. 



the little sheet known as Rodeo Lagoon. In places, the cliff has 

 retreated inland, past the original crest of the hill from which it has 

 been cut, and is thus diminishing in height with its recession. 

 That the land is being encroached upon by the sea with geologic 

 rapidity, is thrust upon the attention in many ways, and is particu- 

 larly noticeable along the line of high cliffs extending from the 

 rocky islet on the western edge of the map, southward to the light- 

 house. The indications of rapid waste may be seen in the abrupt- 

 ness and steepness of the declivities, in the bareness of the rock 

 surfaces, in the occurrence of overhanging masses threatening to 

 fall at any moment, in the evidence of recent sliding, and lastly, in 

 the absence of any considerable amount of beach accumulation. 

 Even in calm weather, the long heavy swell breaks with great force 

 at the base of the cliffs, and there are places under the rock upon 

 which the fog siren stands, where the concussion of a wave on the 

 west, is seen to be followed by a hissing jet of spray, issuing from 

 the opposite or lee side, showing a complete undermining of the 

 mass at that point. It is impossible to say to what distance out to 

 sea the western slope of the hill upon which the old tower stands 

 once extended, but from the contour of the ground it could hardly 

 have been less than half a mile, and was probably more. 



Although the sea has thus cut into the hills and provided good 

 sections of the volcanic rocks, yet the exposures as a whole cannot 

 be regarded as entirely satisfactory, as for more than half the dis- 

 tance, the cliffs are not accessible by ordinary means, and have little 

 or no beach below them. On the land side still more unfavorable 

 conditions prevail, for the hills are heavily covered with a sandy 

 loam, and the contact between the eruptive rock and the sedi- 

 mentary formations lying to the east, is visible only for very short 

 distances at a few isolated points. Owing to these unfavorable con- 

 ditions, it has not been possible to formulate any statement of the 

 mutual relations of all the rocks included in the area which could 

 be accepted as complete, yet some important facts bearing upon 

 these relations may be presented with confidence, and the study of 

 the geology of the surrounding region may be expected to throw 

 light upon such points as are obscure in the very limited area under 

 discussion. 



