496 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



OWENS 

 VALLEY 



Fig. 31.2. Generalized diagram of part of tilted Sierra block. The great fault fractures that 

 separate the Sierra block from the Owens Valley block, on the east, are shown by a single line. 

 The height and slant of the Sierra block are much exaggerated. The streams are shown in their 

 characteristic arrangement, the main rivers flowing down the western slope but many of their 

 tributaries in directions approximately at right angles to them. No specific streams are represented. 

 In front is a strip of the Great Valley of California, whose thick layers of sand and silt, derived 

 from the elevated part of the Sierra block, bury the sunken part. At the back is a strip of Owens 

 Valley, veneered with a thinner layer of sediment. After Matthes, 1930. 



(1935), Gianella and Callaghan (1934); those in southern Nevada by 

 Longwell (1930); and those in southern Oregon and northeastern Cali- 

 fornia by I. C. Russell (1884) and R. J. Russell (1928). In some places 

 these scarps have clearly been developed between the hard rocks of 

 the range and the gravel of the valley. Commonly, however, they are 

 found in the gravel some distance from the range front, and tend to be 

 more irregular than the front in plan. Although most of the recent scarps 

 he at or close to range fronts, some are also found in the intervening 

 valleys (Gianella, 1934; Gianella and Callaghan, 1934) and within the 

 mountain ranges (Callaghan and Gianella, 1935). Many of them are 

 accompanied by hot springs (I. C. Russell, 1884) or are coincident with 

 volcanic cones (Knopf, 1918). 



Nature of Block Faults 



The Sierra Nevada Range is a westward-tilted fault block. See Fig. 31.2. 

 The faults that border the east front of the range are staggered in map 

 plan. Along the great escarpment that faces Owens Valley there may be 

 a single fault, or perhaps a set of closely spaced parallel faults; but farther 

 north the successive offsets in the front of the range indicate the existence 





jn 



3Z 



otc <z 



lis is I „ 



5* o uj< 



oar 



2 



Q 



ZtU 



OO 



sz 

 << 



111 -W 



2* I 



(0(9 



25 bJUi 



z~ (no 



<-> o< 



40 NEVADA! UTAH 



-JO 



UJ< 



ICC 



U/LJ 



*o 

 <tz 

 z< 



(nir 



of? ^ J^\ ^ Z "NEVADA! UTAH - 1 - 



200 Miles 



Fig. 31.3. Diagrammatic section from central Nevada to western Utah. Reproduced from 

 Osmond, 1960. Solid black represents tilted Tertiary volcanic deposits. The ranges can be 

 interpreted as being the remnants of four large anticlines, A, and intervening synclines, B. 



of discontinuous northward-trending fractures that replace one another 

 at intervals, thereby splintering the northwestward-trending margin o 

 the block on a large scale. From the neighborhood of Lake Tahoe, which 

 itself lies in a trough produced by the subsidence of a great splinter, Ion 

 lines of faulting diverge in northerly directions, each marked by ar 

 escarpment of its own. Northward the eastern margin of the Sierra blocl< 

 becomes progressively more irregular, and the displacements are distrib 

 uted over a belt that broadens gradually to a maximum of 50 miles 

 Some of the escarpments measure but a few hundred feet in height 

 and the highest do not exceed 2000 feet (Matthes, 1930). 



Fig. 31.4. Diagrammatic sections of southwestern Utah. Section A from the Nevadan boundaf] 

 to the High Plateaus, and section B from the Escalante Desert to the High Plateaus. The blaci 

 areas represents Tertiary volcanic deposits. Reproduced from Mackin, 1960. 



I 



