378 



University of California Publications. [Geology 



SUGGESTIONS AS TO CORRELATION 



The later Cenozoic history of the western Mohave Desert 

 apparently exhibits marked similarity with the sequence of 

 events in the southern Coast Ranges during that time, as well 

 as to the adjoining Great Basin region. 



According to Ball, 17 the second Tertiary rhyolite is every- 

 where in southwestern Nevada and eastern California separated 

 from the overlying Siebert lake beds by a marked erosional 

 unconformity. The Siebert lake beds, originally described by 

 Spurr from the Tonopah region, 18 are correlated by Ball with 

 the Truckee sediments of the Pah-Ute Lake, referred to the 

 Miocene by King, 10 and with the Esmeralda formation, described 

 by Turner,'-" in the Silver Peak Range. In addition he finds 

 beds which he refers to the Siebert in many localities throughout 

 the southern Great Basin. In the Southern Klondike Hills and 

 the Silver Peak Range rhyolites and silicious latites and dacites 

 are interbedded with the Siebert lake beds without erosional 

 unconformity. Ball believes the second rhyolite to be largely 

 of early Miocene age, the andesite and dacite to be also of com- 

 paratively early Miocene age, the third rhyolite to cover the 

 middle and late Miocene and early Pliocene, and the basalts to 

 range in age from the Miocene to Pleistocene, the major extru- 

 sions occurring in late Pliocene and Pleistocene times. The 

 Siebert lake beds are therefore, in Ball's opinion, early upper 

 Miocene in age. 



Ball summarizes the Cenozoic history of southwestern Nevada 



and eastern California as follows : 



The Eocene inaugurated the Tertiary period of volcanism and lake 

 sedimentation processes, accompanied by important deformation, erosion, 

 and ore deposition. The Tertiary igneous rocks, being largely in flows, 

 in contradistinction to the intrusive post-Jurassic rocks, produced but 

 little contact metamorphism. The permanency of the structural lines, 

 initiated probably in early Cretaceous time, has already been mentioned. 

 Along these lines the Tertiary deformation occurred, while many of the 

 main lava extrusions burst from north-south vents along pre-Tertiary 



it U. S. Geol. Surv., Bull. no. 308, pp. 32-36 and 40-42, 1907. 

 is U. S. Geol. Surv., Prof. Pap. 42, 1905. 



19 Geol. Expl. of the 40th Parallel, vols. I and II, 1877 and 1878. 



20 21st Ann. Kept., U. S. Geol. Surv., pt, II, pp. 191-226, 1900. 



