] Beid: The Geomorphogeny of the Sierra Nevada. Ill 



northwest from Marlett Peak. On the east side of Little Valley 

 more detached areas of the plateau are found. The map fails 

 to express well this geomorphic feature. Furthest north are 

 the areas near Slide Mountain. South of Marlett Lake, Snow 

 Valley Peak is a distinct plateau remnant which owes its un- 

 usual height to faulting. The whole slope from this peak to 

 Eagle Valley consists of a plateau remnant faulted into a series 

 of steps, to be described fully in the proper place. Further 

 south lies the Genoa plateau, a striking feature of the landscape 

 from all points of vantage around the lake. 



The fact that the separate areas of the high plateau have con- 

 siderable range in elevation, for instance 6,700 northeast of Little 

 Valley, 8,300 at Genoa Peak, and a little over 9,000 at Slide 

 Mountain, may be urged against their definite correlation. The 

 facts which favor such correlation are : ( 1 ) the splendidly pre- 

 served character of the plateau; (2) in each particular locality 

 there is but one such surface; (3) the intense faulting of the 

 region is amply sufficient to account for all hypsometric differ- 

 ences; (4) in spite of the fact that all plateau remnants are 

 isolated, the separate areas occur in chain-like arrangement from 

 north to south, and two contiguous portions are separated clearly 

 by a fault with a downthrow of the lower; and lastly (5), the 

 similar characteristics of all the remnants, giving in the field the 

 immediate impression that all are but parts of a single surface of 

 peneplanation. For these reasons it is held that there is repre- 

 sented but one plateau. 



Significance of Summits and Plateau. — If one stands upon 

 the summit of Mt. Tallac, upon the shoulder of which occurs a 

 remnant of the high plateau, this old surface is seen to be hyp- 

 sometrically identical with the larger portions of the Tertiary 

 peneplain that occur to the south sloping down gently to the 

 west, from elevations of 9,000 on the east. Monument Peak and 

 the group of high mountains clustered about Freel Peak, all just 

 south of Genoa Peak, belong to the same zone of high plateaus 

 and summits. Thus Lake Tahoe is surrounded on the south, east 

 and southwest by remnants of the old Tertiary peneplain. There 

 is then possible a correlation between the high plateau zone of 

 the Tahoe area with Lawson's sub-summit plateau in the Upper 



