LATER TERTIARY (MIOCENE AND PLIOCENE). 



819 



J-K 11. NEVADA, OREGON, AND IDAHO. 



The Miocene and Pliocene sediments of Nevada and adjacent parts of Oregon 

 and Idaho have been described by King under the names Truckee and Humboldt, 

 respectively, and Cope has applied the name Idaho formation to certain Pliocene 

 deposits. King ^"^^ postulates an extensive lake (Pah-Ute Lake) and says : 



The beds of this lake, to which, in the Fortieth Parallel area, I have given the name of 

 Truckee Miocene, are made up of, first, detrital rocks and gritty sandstones, with more or less 

 conglomerate, -never over 150 feet. Over this he about 250 feet of palagonite tuff, which, for 

 reasons already described, is referred to the age of the augite andesites; over this, 250 to 300 

 feet in Nevada, with a greater thickness in Oregon, of infusorial sihca, followed by 120 feet of 

 sandy, gritty rocks, purely detrital, but containing always a considerable amount of infusorial 

 silica, succeeded by a fresh-water limestone of about 60 feet, in its turn succeeded upward by 

 250 feet more of detrital grits, which give way to an enormous formation of volcanic tuffs of 

 the trachytic period. The thickness of these trachyte muds in Nevada can not be less than 

 2,000 or 3,000 feet; in Oregon, according to the observation of Prof. Marsh, they are even 

 more fully developed. It is in these volcanic muds that the enormously abundant Miocene 

 fauna of this lake is mostly entombed. Out of the grits overlying the limestone in Nevada 

 have been obtained teeth of a rhinoceros, probably R. facificus. 



At the close of the Miocene, according to King, the Truckee strata "were 

 thrown into bold folds, their dips reaching angles of 30°." Louderback^^''* recog- 

 nizes "a certain amount of deformation in later Tertiary." 



Ball ^** gives an account of the relations of igneous rocks and lake beds in 

 southwestern Nevada and eastern California, from which the following partial 

 columnar section and extracts are taken: 



Columnar section {in fart\ of rocks of southwestern Nevada and eastern California. 



Quaternary. 



Tertiary. 



Carboniferous. 



Pleistocene and Re- 

 cent. 



Pliocene. 



Miocene. 



Eocene. 



Pennsvlvauian. 



Rhyolite. 



Unconformity 



Siebert lake beds, with rhyolite and basalt flows. 



Older alluvium, with Pliocene lake beds at base. 



Rhyolite. 

 Unconformity- 

 Basic andesite. 



Second rhyolite, with minor basalt flows. 



Monzonite porphyry and acid andesite. 



Unconformity 



First rhyolite. 



Unconformity 



The Tertiary rocks include a number of igneous rocks, lava flows, and fewer intrusive 

 masses, and sediments laid down in lakes. * * * 



The oldest of the Tertiary rocks is a rhyolite which occurs in Stonewall Mountain. This 

 occupies a similar stratigraphic position with rhyolites in the Panamint Range, in the Rands- 

 burg district, and near Daggett in the Mohave Desert, which, according to Spurr, lie beneath 

 "lake beds which are probably, in part at least, Upper Eocene." This rhyolite in Stonewall 

 Mountain is cut by dikes of quartz monzonite porphyrj^ and quartz syenite, which are probably 



