812 



GEOLOGY 



Ellensburg 

 Formation 

 1000-1500 ft. 



Yakima 

 Basalt 

 1000-2000 ft. 



Taneum 

 Andesite 



! Formation 

 I 1000ft. 



eastern California and Oregon, reaching great thicknesses (l.nno 

 feet, King) at some points in the vicinity of the 40th parallel. In 



general, they are made up of sandstones. 

 conglomerates, volcanic debris, infusorial 

 earths, and fresh-water limestones. Other 

 areas of deposition, some of them lakes, 

 existed during the Miocene in Nevada 

 (Esmeralda formation) and Montana 

 (Bozeman formation). 



Farther east, on the western part of 

 the Great Plains, the deposition of the 

 White River beds may have continued for 

 a time after the beginning of the Miocene, 

 as indicated by the fauna of the upper- 

 most beds. Late in the Miocene period. 

 aggradation seems to have been renewed 

 in the same general area, and the L<>u/> 

 Fork formation, thin but extensive, was 

 spread out over great areas, from South 

 Dakota to Mexico. The lacustrine 

 phases of this formation are probably 

 less extensive than the subaerial. 1 To 

 the north, the Loup Fork beds are often 

 unconformable on the White River beds. 

 and like the latter have given rise to 

 "bad land" topography. 

 Lake and other terrestrial deposits, largely of volcanic material, 

 are known north of the United States, especially in that part of 

 British Columbia 2 between the Coast and Gold ranges. Mio< 

 deposits are known in Alaska, but erosion rather than deposition 

 was the dominant process there so far as present data show. 



Igneous activity during the Miocene. The wide-spi vad iuneous 

 activity which began with the close of the Cretaceous continued, 

 and perhaps reached its climax during the Miocene. Iun 

 materials abound in the sedimentary formations of the 



1 Haworth, Univ. Geol. Surv. of Kan., Vol. II, p. 281. 



2 Dawson, G. M., Trans. Royal Soc. of Canada, 1890. 



Easton 

 Schist 



I! 



Fig. 546. Columnar sec- 

 tion showing the suc- 

 cession of formations in 

 central Washington. (G. 

 O. Smith, U. S. Geol. 

 Surv.) 



