778 GEOLOGY 



tains of that name, and another, a little later, in the basin of the 

 Green River, both in Wyoming, and in Utah south of the Uinta 

 Mountains. It may have been during this stage, too, that the 

 volcanic tuff (San Juan formation, 2,000 feet and less thick) of the 

 Telluride region was made. 1 This last formation is of interest as 

 an index to the vigor of volcanic action in this region. 



4. The Uinta stage 2 followed the Bridger. Deposition was then 

 in progress in southeastern Utah and southwestern Colorado. The 

 deposits occupied a part of the area covered by the Wasatch and 

 Bridger formations, so that these formations are found in super- 

 position, in some places. The Uinta beds now have an altitude of 

 as much as 10,000 feet, though they were probably deposited at a 

 much lower level. 3 



The northwest. In the northwest there are Eocene formations 

 not definitely correlated with the preceding stages. Thus in 

 northern Oregon, there are late Eocene beds of terrestrial origin 

 (Clarno formation, largely volcanic tuff 4 ) in the John Day basin, 

 which was the site of aggradation during a large part of the Tertiary. 

 In Washington two thick sedimentary formations (the Xir<uik, 

 early Eocene, 3,500-5,000 feet, below, and the Roslyn, 3,500 feet) 

 of Eocene age and non-marine origin, are separated by 300-4,000 

 feet of basalt. The Payette formation of Idaho, said to have been 

 accumulated in a lake formed by the damming of the upper basin 

 of the Snake River by the early lava-flows of the Columbia River 

 region, 5 is now referred to the Eocene. 6 Eocene beds of terrestrial 

 or volcanic origin are imperfectly known in many other places west 

 of the Rocky Mountains. The erosion of the Eocene has ^iven 

 rise locally to the topography characteristic of "Bad Lands." 



General considerations. It has been customary to regard the 

 Eocene and later periods as much shorter than those of the 1'alen- 



1 Purington, Telluride, Colo., folio, U. S. Geol. Surv. 



2 Here belong the Diplacodon beds of Marsh and the Browns Park group 

 of Powell; Geol. of the Uinta Mountains, pp. 63, 168, 208. 



3 It is possible that some of these beds should be referred to the ( Mi^orrnr. 



4 Merriam, Jour. Geol., Vol. IX, p. 71, and Bull. Univ. of Cal., Vol. II. p. 

 285, and Knowlton, Bull. 204, U. S. Geol. Surv. 



5 Lindgren and Drake, Nampa and Silver City, Idaho, folios, U. S. 

 Surv. 



'Knowlton, op. cit., p. 110. 



