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University of California. 



[Vol. 2. 



a sharp ridge or series of knobs of the Sugar Loaf type. Inasmuch 

 as the forms of the hills are due entirely to erosion, it is apparent 

 that the geomorphic prominence of this formation is due to the 

 contrast in the degree to which it has yielded to the attack of 

 erosive forces, as compared with the formations on either side of it. 

 We have seen that the sandstones of the Shasta-Chico series yield 

 hill forms which have in general smoothly-flowing contours and 

 rounded profiles. Along the line of the Monterey formation the 

 declivities are steeper and the profiles are more sharply convex. 

 The formation to the east of the Monterey formation is softer and 

 yields even more rapidly to erosion than the sandstones to the west 

 of it, and in consequence the surface is lower and the slopes gentler. 

 It is, therefore, due to differential erosion, or degradation, of the 

 land mass of which the Monterey formation forms a part, that its 

 relief is expressed so boldly. Were it composed homogeneously of 

 chert, Sugar Loaf would be much more rugged and precipitous 

 than it is. Its degradation is greatly facilitated by the soft shale 

 layers, and the disintegration of the chert is wholly mechanical. It 

 breaks up into sharply angular, cuboidal fragments or into flat 

 chips which gradually move down the slopes or accumulate on the 

 ridge tops. The formation in general yields but a very thin and 

 poor soil. 



The geomorphic features which thus characterize the formation 

 in its extension southeastward are even more striking in its north- 

 westward prolongation. The reason for this is that to the north of 

 Skyline Ridge the Canon fault, which has been referred to above, 

 lets down against the westerly side of the formation a much softer 

 set of rocks than the Shasta-Chico sandstones, and out of these soft 

 rocks the central portion of the amphitheater-like depression of 

 Strawberry Canon has been eroded; so that the rocks of the Monte- 

 rey formation present a very precipitous wall to the center of the 

 amphitheater. This steep wall has been notched transversely by the 

 several tributaries of Strawberry Creek, and we thus have a sharp 

 ridge chopped up into a series of prominent knobs, of which 

 Monument Hill is the largest and most typical. 



The extension of the formation to the northwest is, however, 

 quite limited, for the Canon fault, which on Skyline Ridge dis- 



