352 



University of California Publications in Geology [Vol. 8 



The type locality of the Truekee beds of the Fortieth Parallel 

 Survey lies east of Reno, in the Kawsoh Mountains and along the east 

 edge of the Virginia Range. 8 In searching for mammalian remains 

 in beds presumably belonging to the Truekee group between Reno 

 and Verdi in June, 1914, the writer obtained part of a tooth of a 

 proboscidean of the mastodon type. The specimen is probably not 

 determinable specifically, and cannot be definitely determined as iden- 

 tical with forms represented by fragmentary mastodon remains known 

 from the Esmeralda of Stewart and lone valleys. The age of the 

 Truekee has heretofore been regarded as Miocene or Pliocene. As 

 proboscideans are not definitely known in America in horizons older 

 than middle Miocene, the portion of a mastodon tooth obtained indi- 

 cates that the Truekee beds are probably middle or upper Miocene 

 or younger. The Truekee beds are in general similar in appearance 

 to the Esmeralda, and it is not improbable that the correlation of 

 the Esmeralda with the Truekee, suggested by Spurr and others, 9 is 

 correct. 



FANGLOMEKATE MANTLE 



One-half or more of the area underlain by Esmeralda beds in 

 Stewart and lone valleys consists of smooth mesa surfaces (pi. 38 

 fig. 2). Apparently these even surfaces extended over the entire 

 valley areas before the latest cycle of dissection of the beds com- 

 menced, as they are now interrupted only by badland areas produced 

 by present-day erosion. The separated areas were not originally parts 

 of a single surface, but represent different levels successively cut on 

 the beds. Their relation appears to be that of remnants of a series 

 of stream terraces. The different levels are separated vertically some- 

 times by only a few feet ; on the west side of Stewart Valley, however, 

 there are shoulders, composed of laeustral beds, running out from 

 the Gabbs Valley Range, on which the mesa remnants lie perhaps 

 125 feet above the level next below them. The different mesa areas 

 therefore differ somewhat in age, the low-lying areas having been cut 

 at a later date than those lying above them. 



The mesas are protected, not by a cap of lava, but by a resistant 

 layer of fanglomerate, usually five to twenty feet in thickness. This 



s King, Clarence, U. S. Geological Exploration of the Fortieth Parallel, vol. 

 1, p. 412 et seq., 1878. 



o Spurr, .J. E., Ore Deposits of the Silver Peak Quadrange, Nevada, U. S. 

 Geol. Surv. Prof. Paper, no. 55, p. 20, 1906. 



