82IITH, PHYSIOGRAPHY OF SEYKOMISH BASI?^"^ 211 



The southwest winds, heavily saturated Avith warm waters from the 

 Japan current, are compelled to rise 7000 feet or more in crossing the 

 Cascades. As a result of this rise the pressure of the overlying atmos- 

 phere is reduced so that the air loses density and the temperature drops. 

 This tends to cause heav}^ precipitation, and in fact the moisture is so 

 completely taken from the atmospheric currents that eastern Washington 

 has a semi-arid climate. 



Precipitation comes chiefly in the months of minimum temperature 

 and a very large proportion of this precipitation is in the form of snow. 

 At Cascade, a little way down the eastern slope of the Cascade Moun- 

 tains, and just east of Scenic, D. C. Shafer says 110 feet of snow fell in 

 one year.^* 



Willis tells us that the canyons of the Cascades were cut to advanced 

 youth in the Twisp or pre-giacial stage. The canyons were over-deepened 

 to an unknown amoimt h_v giaciation in the Chelan stage and lie gives the 

 name Stehekin to the stage succeeding glacial occupancy.^^ 



Little can be said of the Twisp stage; there are but few unglaciated, 

 elevated areas and all valley sides have been affected by giaciation. A 

 majority of them present the straightened courses and the nearly vertical 

 walls which are characteristic of alpine giaciation. These vertical walls 

 rise to a height of hundreds of feet, but the pre-glacial slope beginning at 

 the upper limit of the vertical wall has been so modified by extremely 

 active geologic processes of ice, water and insolation that no accurate data 

 of over-deepening are ventured in this paper, though it is probable that if 

 the extent of such modifications could be determined more or less reliable 

 information could be obtained. 



Tlie amount of Stehekin cutting varies with varying factors; the depth 

 of the stream gorge of Dorothy Creek is about 40 feet and this has ap- 

 13arently been cut by swiftly running, but sediment free, water. Maloney 

 Creek runs in a gorge about 80 feet deep, but here the erosion has been 

 chiefly in Eocene sediments and by swiftly running water abundantly 

 provided with cutting tools. The Great Falls of Miller Eiver seem to 

 have retreated in resistant granodiorite a distance of some 60 feet. Many 

 other examples could be cited, but they would only show that Stehekin 

 cutting has been comparatively slight and therefore the stage is not very 

 far progressed. This means that at a comparatively recent time the 

 tributary valleys of the Skykomish and Snoqualmie Eivers were occupied 

 by glaciers. 



"D. C. Shafkh : A Waterfall to Haul Mountain Trains. World's Work, Vol. 17, p. 10. 

 982. 1908-1900. 



^= B. Willis: Contributions to Gcoloiiy of Washington. Prof. Paper 19. pp. 80-83. 

 1908. 



