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University of California Publications. [Geology 



substantiated by the faulting in Little Valley, described later. 

 Further investigation in the field will undoubtedly throw more 

 light upon this particular question. 



Two other creeks flow in longitudinal courses over part of 

 their lengths west of Snow Valley Peak. These both flow over 

 the trace of the same fault-plane, one that is strongly marked 

 in almost unnotched fault-scarps. And small as are these creeks, 

 there is one very important point to be made clear by an examina- 

 tion of their different branches. In the creek west of Marlett 

 Lake there are a number of branches. The central one and the 

 northern carry about the same amount of water. Yet the central 

 one has cut hardly a notch, though flowing at a somewhat higher 

 grade. The northernmost, however, flows in a decided angle in 

 the fault-scarp. There is an east-west fault passing through the 

 north end of Marlett Lake, bounding the down-dropped block. 

 It finds expression in the notch of the northern branch of the 

 creek, which thus takes on a new value. Similar occurrences can 

 be noted elsewhere on the sheet mapped. The south branch of 

 the creek just west of Marlett Lake and the north branch of the 

 creek west of Snow Valley Peak flow over the fault-plane that 

 forms the eastern boundary of the westernmost fault-block in 

 this section. There are thus two lesser faults between Snow Val- 

 ley Peak and the larger fault forming the east boundary of Lake 

 Tahoe. This step-like feature of the faulting is its most constant 

 characteristic. 



The important physiographic criteria of faulting in the area 

 of plutonic rocks can be briefly summarized thus, in order of 

 relative importance: (1) unmistakable fault scarps; (2) step- 

 like character of mountain profile, accompanied by corresponding 

 rapids and gentler courses in the streams; (3) steep-cut rocky 

 buttresses separated from main peak or ridge by distinct cols; 

 (4) sharp jogs in an otherwise smoothly flowing slope, which may 

 or may not be occupied by small creeks. On Prison Hill there 

 are no streams ; just west across the valley there is a very small 

 flow in wet weather ; in the higher mountains the creeks are fre- 

 quently quite large; (5) consequent longitudinal streams flowing 

 in distinct valleys, often of considerable size and with a floor 

 of coarse granite sand. 



