Vol. G] Eeid: The Geomorphogeny of the Sierra Nevada. 153 



Little Valley and Lake Tahoe. This would mean that the Tahoe 

 Moat was blocked out in early times, and reached its final form at 

 a later period. In the light of our present incomplete knowledge, 

 more discussion would be out of place. 



STEUCTUEE AND GENESIS OF LITTLE VALLEY. 



The four periods of faulting, with the principal direction of 

 each, have been noted for the Little Valley area. These faults 

 are along rectangular lines, north-south and east-west. A very 

 casual glance at the topographic map reveals two prominent 

 north-east and south-west fault lines that call for explanation 

 and a determination of their proper position in time. To this 

 end the complete structure and genesis of Little Valley must be 

 discussed. To summarize what has been already stated, the first 

 north-south faulting formed the lower scarp rising on the west 

 side of Washoe Valley, and probably formed but one crest in this 

 east ridge of the Sierra Nevada. The second period of faulting 

 in the same direction formed the west scarp, the high west ridge, 

 the present boundaries of Lake Tahoe and of Lakeview, and es- 

 tablished the important north-south fault-line upon which Little 

 Valley was formed. The next period of faulting was in an east- 

 west direction, and displaced the Little Valley fault-line by the 

 elevation of Slide Mountain. Also the floor of Little Valley was 

 faulted at the distinct jog in the creek and at other important 

 places not yet discussed. The last east-west faulting was small 

 and did not change the valley characteristics. This summary 

 leaves much unexplained and leaves out of consideration some of 

 the essential features connected with Little Valley. 



From what has already been noted regarding Little Valley it 

 is evident that the present form and complete structure are pos- 

 terior to the last period of north-south faulting ; the earlier east- 

 west faulting movements have considerably modified the valley. 

 Upon analysis of the dynamics of the faulting it appears that 

 this east-west movement is responsible for the main structural 

 features. 



The lower east ridge is already divisible into four blocks, each 

 of which is broken by a number of lesser faults. The first block 

 occupies the area between the Slide Mountain fault and the 



