70 



JOHN A. REID 



sent a northerly continuation of the same beds. In general these 

 beds dip slightly to the north; locally they are either gently folded, 

 or broken and faulted near the basalt flows. The lowest elevation 

 of their exposures is 3,760 feet, south of Keeler; the highest is 5,160 

 feet, nearer Darwin. This gives a vertical range of at least 1,400 feet 

 and a height above the present lake of 1,560 feet. Lake beds are 

 noted by Fairbanks,' occurring on the west flank of the Coso 

 Range, which correspond in elevation with those on the east. 

 These lake deposits probably extended northward and joined with 

 those of Wancobi Lake of Walcott.^ Spurr^ has given a brief resume 

 of the existing knowledge of these, and concludes that no local faulting . 

 has been the cause of the elevation of the Wancobi beds. In the Coso 

 strata many small faults have occurred, but it is very doubtful if their 

 present position is due in the main to differential motion of the under- 

 lying rocks. If this be so, it is entirely probable that one large lake 

 existed over this region, as Spurr^ concludes, which was drained by 

 tilting north and south from a point in the vicinity of Mono Lake. At 

 this latter locaHty the beds are at elevation 7,100 feet; at Wancobi em- 

 bayment 7,000 feet; and near Darwin at 5,200 feet. These figures 

 would indicate a differential tilting, which combined with the fact 

 of much faulting of the basalt overlying the lake beds southeast of 

 Keeler (see Fig. 5), makes it very probable that local elevation in the 

 Inyo Range has caused a part of the present elevation of the lacustrine 

 formation. 



A further point noted in the stream gullies west of Darwin, is that 

 the granite, though showing no faults of size, is intensely fractured 

 as if squeezed between powerful jaws. The complexity of these small 

 movements is well shown by the quartz veins, which are most intri- 

 cately displaced in small blocks. The prevailing mode of this dis- 

 placement consists of a series of northeast-southwest faults dipping 

 northerly, along which the north walls have moved westward. The 

 best-developed joints strike N. 40 W. with a dip of 85° northeast. 

 The rocks are deeply weathered, with the surface covered by rounded 

 boulders of disintegration. 



1 American Geologist, Vol. XVII, p. 69. 



2 Journal of Geology, Vol. V, pp. 340-48. 



3 Bulletin 208, U. S. Geological Survey, pp. 209, 210. 



