224 J. E. SPURR — ORIGIN AND STRUCTURE OF THE BASIN RANGES 



being zones of weakness, and hence easily eroded. In this region, as 

 in that of northwestern Utah, if the mountain ranges are mainly due to 

 erosion, it follows that the intervening valleys originated in the same 

 way. 



MANGES OF NORTHWESTERN NEVADA 



HdvaUah range. — The northern portion of the Havallah range* is es- 

 sentially an anticlinal fold of Triassic rocks. Adjacent to this anticline 

 is a parallel syncline, which lies to the west of the main mountain range. 

 To the east of the main ridge is a syncline, which forms a subordinate 

 ridge between Iron point and Golconda, on the Central Pacific railroad. 

 The northern end of the range is supi)osed by Mr King to be determined 

 by a transverse fault. 



Mr Plague, who has written a more detailed description of the range, 

 does not mention the fault, but gives more information about the folding. 

 The highest portion of the mountains, which is the center of the anti- 

 cline, consists of dense, tough quartzites, while the overlying strata on 

 the flanks are interstratified sandstones, slates, and shales. Along the 

 very axis of the anticline is a deep canyon. f Southward from here, at 

 Bardmass pass, the governing influence of the underlying rigid quartzite 

 being no longer felt on account of its lying so far below the surface, the 

 range consists of two gentle folds, an anticlinal and a S3^nclinal, the latter 

 forming most of the mountains, while the axis of the anticline Iffes along 

 the eastern foothills.J 



The synclinal ridges described are evidence of powerful erosion, while 

 the hard resistant core of the chief anticlinal fold explains the origin of 

 this ridge also as an erosive feature, in the same way as in the East 

 Hum])oldt and Pinon ranges. 



Pdh Ute range. — The Pah Ute range ^^^ has also a governing anticlinal 

 fold. A series of chiefly north-and-south faults has confused the struc- 

 ture. Mr King's descriptions imply that these faults have a direct in- 

 fluence on the topography. 



Mr Hague || describes the central core of the mountains as made up of 

 granite and granitoid rocks, these being overlain by Triassic quartzites, 

 and these by limestones and shales. 



That erosion has actually heen very active in this range is shown by 

 the enormous thickness of rocks (15,000 to 17,000 feet at leasts) which 

 has been stripped ofif from the underhnng basement. 



* King : Op. cit,, p. 741. 



1 1' ortieth Paralk'l, Descriptive Geology, vol. ii, p. 081. 



I Op. cit., p. CS:}. 

 g King : Ibid. 



II Op. cit., p. G89. 

 HKing: Op. cit., p. 277. 



