448 OSCAR H. HERS HEY 



canyon as the present bottom of the gorge. Possibly a small 

 glacial tongue extended down this valley at times, but the bowl- 

 ders on the south terrace are so numerous and are piled up above 

 the soil in a way to indicate that they were carried over the crest 

 of the ridge on the south and rolled down to the bottom of the 

 valley. Since this event, Salmon River has cut a rock gorge 

 under the older valley, 50 to 75 feet deep. // descetids several 

 hundred feet m less than a quarter of a ?nile. 



This canyon I attribute to late Wisconsin and post-Winconsin 

 stream erosion. It is rather larger than I am accustomed to for 

 the product of that time, but the flat platform above the gorge, 

 in which this canyon is partly excavated, certainly was glaciated 

 during the last or Wisconsin stage. This canyon is proportionally 

 somewhat smaller than that eroded since the abandonment of 

 Channel C down the river, but at first thought there does not 

 seem to be any very great contrast between them. However, on 

 the ground, the impression is very quickly made on the observ- 

 er's mind that this upper canyon is much newer than that down 

 the river which succeeded Channel C. Conditions for erosion 

 are exceptionally favorable because it is very high grade. The 

 river descends through it in a series of falls, with perpendicular 

 drops at two places of over 20 feet. The rock is not excep- 

 tionally resistant. If this same river had flowed through this 

 gorge since the abandonment of Channel C, it could not have 

 failed to have cut back to the center of the broad valley above 

 instead of only cutting a notch in the edge of the broad, inward- 

 sloping valley rock-floor. 



Tongues of ice from the m^ain Salmon River glacier undoubt- 

 edly overrode the col during the earlier glacier stages, but during 

 the interglacial or minimum stages, Salmon River did not flow 

 through the gorge, as otherwise it would have completely 

 destroyed the very high grade character of this short section of 

 its course. The broad valley above the gorge was drained by 

 Coffee Creek until late in the Wisconsin or last glacial stage as is 

 evidenced by a broad valley eroded in the earlier glacial deposits 

 just outside of the terminal moraine of the Salmon River glacier 

 in its last stage. This terminal moraine is trenched by an insig- 



