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University of California. 



[Vol. 3 



of maturity is impressed upon the face of the country, and 

 one is staggered by the contrast which it presents with the wilder 

 features of the mountains to the north. The geomorphy here is 

 clearly paragenetic with that - of the High Valley Zone, and will 

 be further discussed in that connection. 



Significance of Upland and Plateau .—When we attempt an 

 interpretation of the surface features, which have been desig- 

 nated the Summit Upland and the Sub-summit Plateau, a number 

 of interdependent questions arise for which it is difficult to find 

 satisfactory answers. We must first ask : Has the configuration 

 of the Summit Upland any relation to the original upper surface 

 of the granite? It has already been pointed out that the contact 

 surface of the granite with the roof of sedimentary strata, which 

 once presumably arched over it, would constitute an important 

 structural feature, not without influence upon the course of 

 erosion. If we may judge from the Mineral King belt and from 

 analogy with the northern Sierra Nevada that contact was an 

 undulating and locally an acutely uneven surface. The sedi- 

 mentary rocks of the Mineral King belt are much more easily 

 eroded than are the granite, and if, instead of being sunk down 

 into the granite, as at Mineral King, they formed a shell or 

 covering, that covering might be stripped off and expose the 

 more resistant granite, the surface of which would then be 

 determined by the configuration of the contact plane between the 

 two classes of rocks. In this way there might be evolved flat, 

 gently inclined, or undulating surfaces, as for example such as 

 we find at the summit of Table Mountain, the summit of Mt. 

 Whitney and Sheep Mountain; and, as a detail of such an 

 undulating surface, we might have pronounced terrace effects, 

 such as characterize the summit region between Sheep Mountain 

 and Circrae Peak. Now, of course, it may be urged that such a 

 surface would still be a surface of erosion. But, while this is at 

 once conceded, the recognition of the possibility of such a 

 structural control as that above indicated introduces an impor- 

 tant factor in the interpretation of the historical significance of 

 that surface. It presents, in its upper parts, flat areas, gently 

 inclined, undulating and smoothly rounded slopes, which would 

 usually be interpreted as characterizing senility of geomorphie 



