338 University of California Publications in Geology [Vol. 8 



GEOLOGY OF THE REGION 



The rocks of the Cedar Mountain region present a considerable 

 variety of types. Great thicknesses of old limestones and marbles, 

 masses of granular intrusives, and extrusive lavas of both acidic and 

 basic types with their tuffs and agglomerates, constitute the ranges. 

 The rocks flooring the valleys consist of moderately thick sections of 

 Tertiary sedimentaries, which have been described by Turner as the 

 Esmeralda formation, from exposures at the north end of the Silver 

 Peak Range. These beds consist largely of clastic sediments and tuf- 

 faceous materials laid down for the most part in a Tertiary lake. 



The limestones, granular rocks and marbles are clearly much older 

 rocks than the lavas. The latter in places lie unconformably below 

 the Esmeralda beds and are somewhat older, although there is reason 

 to believe that there was also volcanic activity in the region contem- 

 poraneous with the deposition of the lake beds. Lavas also overlie the 

 lacustral beds. 



The discussion of the geology of the region, in so far as it was 

 discerned in the limited time, will be taken up by localities. 



Cedar Mountain 



The rocks of Cedar Mountain are largely limestones interbedded 

 with thin shale layers, intruded by holocrystalline granular rocks. 

 Lavas cover considerable areas in some parts of the range. 



LIMESTONES 



The limestones of Cedar Mountain occur as irregular areas. The 

 rock is usually gray or blue, often dark blue, in color ; on weathered 

 surfaces brownish tints are not uncommon, probably due to a consid- 

 erable iron content. It is locally quite impure, and is often siliceous, 

 grading into cherty phases. It is disposed in layers ranging in thick- 

 ness up to several feet ; between the layers are thin bands of calcareous 

 shale. The limestone layers are themselves banded, apparently due 

 to differences in amount of contained impurities. No considerable 

 masses of sandstones or conglomerates were seen associated with the 

 limestones in Cedar Mountain, such as are reported by Spurr in the 

 Pilot Mountains to the west. 1 



i Spurr, J. E., Bull. U. S. G. S., no 208, p. 104, 1903. 



