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University of California. 



[Vol. 2. 



the canyons, similar cutting in earlier deposits has taken place, to 

 about the same depth. The upper limits of the deposits in the 

 Little Harbor region were not determined, but they were noted up 

 to about 300 feet. 



Santa Rosa, the second in size of the islands of the northern 

 group, is roughly rhombic in outline, with a length of about seven- 

 teen miles, and a width of about eleven. Its main watershed con- 

 nects the eastern and western extremities of the island, bending to 

 the south, and lying considerably nearer to the southern than to the 

 northern coast throughout its length. The minor ridges have a 

 general radial arrangement about the central portion of this divide. 

 That portion of the main divide which forms the island's crest is a 

 little to the southwest of the center of the island, and runs in an 

 easterly and westerly direction. This region has an average alti- 

 tude of a little over 1,500 feet, a height not even approximated by 

 any other portion of the island. The main ridge here is almost 

 level, having a variation of not more than seventy-five feet for a 

 distance of over three miles. In nearly four miles the variation is 

 less than 175 feet. It would thus appear that Santa Rosa, like 

 Santa Catalina, has suffered planation at an altitude of about 1,500 

 feet. 



The southern half of Santa Rosa is quite rugged, with topo- 

 graphic forms closely resembling those of Santa Catalina. In the 

 northern half the summits are broader and platform-like, the general 

 slope is gentler, the relief not so marked, and the whole character 

 is that of forms cut in much softer rocks than those of the southern 

 half. The effect of the whole is of mature topography, the differ- 

 ences being due to differences in the rocks. The softer rocks are 

 less resistant than those of San Pedro Hill, if the character of the 

 dissection may be taken as a criterion. The forms of the northern 

 half, as in the case of San Pedro Hill, have doubtless been more or 

 less simplified by wave action. The topographic age is believed to 

 be not far from maturity for such soft rocks. The general form of 

 the island as a whole is suggestive of a faulted crust-block, though 

 considerably modified by erosion. 



According to the principles set forth later, pronounced terrac- 

 ing, if it occurs at all, would be looked for only on the gentler, 



