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ELIOT BLACKWELDER 



of these are the Wind River basin, Jackson Hole, Teton basin, 

 Bighorn basin, Green River valley, and many others outside the 

 district here considered. In these wide basins the younger rocks, 

 down to the more or less resistant Triassic(?) red beds, or even 

 down to the Carboniferous terranes, have nearly all been planed 

 off to a common level. It is highly probable, however, that all of 





Fig. 25. — Bad-land topography in the Wind River basin. Shows dominance 

 of the effects of running water even in the driest part of the district. 



the basins were formerly filled more or less completely with the 

 soft Tertiary strata, and that most of the erosion has been accom- 

 plished in them rather than in the older rocks beneath. All are 

 still partly filled with formations of that age, and outliers show a 

 much more complete filling before erosion occurred. 



The floors of these basins are by no means simple flats (Fig. 25), 

 but the details will be discussed more fully in later pages. 



At the intertwined headwaters of the three great river systems, 

 the valleys are still narrow and in part ungraded. There, even 



