320 ELIOT BLACKW ELDER 



are somewhat more resistant and the region is closer to the head- 

 waters of the streams. Westward this inner valley merges into the 

 floor of Jackson Hole. Since the latter is now coated with recent 

 alluvial deposits of unknown depth, it may prove to be somewhat 

 unlike the Wind River basin in origin. If the filling is deep it may 

 signify local warping or faulting, and the appropriate disturbance 

 of stream gradients; but if it is thin, as I think more probable, it 

 may be ascribed entirely to the glacial choking of Snake River. 



Inner trenches of varying widthy but generally similar to those 

 farther east, are observable along Fall or "Hoback" River, down 

 the Grand Canyon of Snake River to its lower valley near Irwin, 

 and also along its southern tributary, Salt River, as far up as Star 

 valley, in Wyoming and Idaho. 



Fig. 38. — Diagram showing the relation of Circle and Lenore terraces to moraines 

 of the {a) Bull Lake, and (6) Pinedale glacial stages. Wind River basin. 



On the whole, the Lenore cycle did not go far, and resulted only 

 in the excavation of relatively narrow valleys with slender and even 

 interrupted floodplains, except in weak strata and along large 

 streams. The moraines of the latest glacial stage were deposited 

 in these valleys, showing definitely that the inner trenches were 

 made just before the last ice advance. 



It will some day be possible, through detailed local studies, 

 to subdivide the Lenore cycle on the basis of terraces, shallow inner 

 trenches, etc. For example, the Snake River in Jackson Hole is 

 intrenched distinctly below the general level of the flat; at the 

 mouth of the Grand Canyon of the Snake, the river has intrenched 

 its gravel-strewn floodplain to a depth of 50-60 feet; and near the 

 mouth of the Hoback River that stream has cut a trench of about 

 the same depth through deposits of gravel into solid rock below. 

 These features are so much more prominent in the Snake River 

 drainage than in the Green River or Wind River basins that I am 



