354 University of California Publications. [Geology 



nous belt of ore-bearing porphyry which traverses the district 

 with a trend in general transverse to the strike of the sedimen- 

 tary strata. It is probable that the rupturing of these folded 

 formations, incident to the injection of the intrusive masses, 

 was accompanied by more or less pronounced dislocations ; but 

 such dislocations were more of the nature of laccolithic lifting 

 of the formations, one part from another, than of faults in the 

 usual sense of the term. 



The only true faulting subsequent to these intrusions that 

 has been detected in the district is of very late date, since the 

 faults traverse the sheets of rhyolite which were poured out over 

 the surface at a time when the latter had been reduced by ero- 

 sion approximately to its present general configuration. These 

 rhyolitic lavas may be early Pleistocene and are certainly not 

 older than late Pliocene, judging from the degree of degradation 

 which the region has suffered since their extravasation. It is, 

 therefore, believed by the writer that the faulting is not older 

 than early Pleistocene. 



Of these faults traversing the district perhaps the most prom- 

 inent in the geological mapping is that which crosses the north- 

 ern flank of White Hill and throws the rhyolite capping of that 

 eminence down into the Palaeozoic rocks. This fault has a 

 general northeast-southwest trend, and the mapping shows that 

 it hades to the southeast at a small angle from the vertical. This 

 is the direction of the down throw and it is thus a normal fault. 

 The down throw brings rhyolite against the Arcturus and Ely 

 formations and against the ore-bearing porphyry. The mini- 

 mum estimated value for the amount of the down throw is 200 

 feet and it may be much more than this, depending upon the 

 reduction which the surface on the upthrow side has suffered 

 since the faulting transpired. 



To the northeast, in the vicinity of Copper Flat the fault has 

 dropped the ore-bearing porphyry against the White Pine shale, 

 and the northeastern boundary of the porphyry has thereby been 

 heaved to the northeast, a distance of about 3,000 feet. 



A second fault of some importance is that which traverses 

 Oeher Valley with a general east-west trend and drops the rhyo- 

 lite of Quarry Hill against the Arcturus limestone. The throw 



