Vol. 6] Eeid: The Geomorphogeny of the Sierra Nevada. 



157 



face. In brief, the hanging block appears to be a remnant of 

 the plateau left in its present elevated position by the down- 

 dropping of a triangular valley block adjoining it on the east. 

 At the end of the second period of north-south faulting, this 

 hanging block formed the west portion of the block just east of 

 the high west ridge block. For the several crust blocks to have 

 moved in the manner indicated it is evident that a compressive 

 stress acted at the point where the plateau remnant meets the 

 west scarp, and a tension existed within the valley, allowing the 

 valley blocks to drop at their south ends while held unmoved at 

 the north. This sort of a movement of the main valley block 

 would tend, in conjunction with the certain amount of torsional 

 stress that was almost certainly set up, to fracture the block 

 along lines radiating from the fixed point, and cause differential 

 movements among the small sub-blocks. This is precisely what 

 seems to have happened in north Little Valley. In south Little 

 Valley a similar downdropping of a valley block has occurred, 

 except in the most southern portion, where differential elevation 

 has been combined with step-faulting, to produce the valley. 

 In this connection it is well to examine Marlett Lake rather in 

 detail. An examination of the map shows that the block under 

 the lake lies between three other blocks, two of which meet at an 

 angle of about 135°. These two blocks occupy their present 

 position because of the compressive stress in a north-south direc- 

 tion set up by the elevation of Snow Valley Peak. The result 

 of the action of this force has induced a tensional east-west force 

 through Marlett Lake block that allowed the latter to drop. This 

 interpretation of the structure is based upon the assumption of 

 normal faulting. This being so, it follows that for an earth- 

 block to drop relatively to the ones adjacent a tensional force 

 must have been in operation. The elevation of Snow Valley 

 Peak, which did occur, must have provided a north-south com- 

 pression if the faulting was normal, and an induced tension at 

 right angles. The faulting of the region is characteristically 

 normal in all its aspects. Further, had the conditions of stress 

 necessary for thrust faulting obtained, with the steep position 

 of its fault-plane great crushing of the rocks would have occurred 

 rather than actual moA'ement of large blocks. Lastly, the same 



