A NOTE ON THE GEOLOGY OF THE COSO RANGE, 

 INYO COUNTY, CAL. 



JOHN A. REID 

 Stockton, Cal. 



The completion of the geological history of the Sierra Nevada and 

 associated ranges appears to rest, for practical reasons, upon the 

 determination, at different times and in different places, of the neces- 

 sary facts. It is with this in mind that the writer presents the follow- 

 ing data, ascertained on a recent short business trip. It is hoped that 

 others may be fortunate enough to be able to dig more deeply into 

 the rocks, both in the locality described and elsewhere in the adjacent 

 regions. 



The Coso Range lies between the Sierra Nevada on the west and 

 the Darwin or Argus Range on the east, separated from each by a 

 long narrow valley. At the north end the Coso Range forms the 

 south boundary of Owens Valley, and extends thence southerly along 

 its main axis for about forty-five miles. The greatest width at the 

 north is twenty miles (see map, Fig. i). A number of general state- 

 ments have been made regarding this pecuHar range, with but Uttle 

 in detail. 



From whatever point of view seen, the Coso Range is strikingly 

 different in appearance from the surrounding mountains. Fig. 2 

 shows the Range looking south from Keeler. The typical appearance 

 is here well outlined. The fiat, nearly horizontal, sky line, with, 

 in general, gentle slopes to the bordering valleys, give an air of maturity 

 not found in the precipitous fault scarps of the Basin Ranges. One 

 comparatively small scarp is seen in the eastern part of the range, 

 facing northeast, and its supplementary scarp occurs in the western 

 portion. The form of the whole is that of a very flat elhptical dome, 

 with its longer axis lying north and south. The periphery of this 

 dome grades into the surrounding valley alluvium. The northern 

 and western flanks are largely covered with basalt flows; the eastern 



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