Studying the Yosemite Problem 



145 



One thing must have become patent from the foregoing 

 pages, namely that the study of a glacial valley such as the 

 Yosemite can scarcely hope to be exhaustive unless it be ex- 

 tended to the higher regions that were the sources of the ice. 

 The need of an acquaintance with these regions soon im- 

 pressed itself upon the investigators and accordingly they de- 

 ployed over the entire headwaters country of the Merced 

 River as well as over the basin of the Tuolumne. The latter 

 territory proved of unusual interest, for it evidently consti- 

 tuted the great central neve field of the middle Sierra and 

 poured its ice not only down the Grand Canon of the Tuo- 

 lumne, but across several passes into the Tenaya and Merced 

 basins, as well as down the canons of the east facing Sierra 

 front. The height attained by the ice and the extent of its 

 various diversions during each separate epoch were ascer- 

 tained with considerable care, while at the same time the rock 

 types present in the area and transported from it by the ice 

 were examined in some detail. Late in September the inves- 

 tigators returned to the Yosemite Valley, and resumed their 

 labors there enriched with an insight into the character of the 

 region that was the birthplace of the Yosemite glaciers. 



A visit was also made to the Hetch Hetchy Valley, the 

 Grand Canon of the Tuolumne and Lake Eleanor. Some 

 valuable lessons in the glacial history of the Sierra Nevada 

 were learnt on that trip, not the least valuable of which was 

 derived from the fact that the ice stream that traversed the 

 Hetch Hetchy Valley was vastly superior in volume and in 

 length to the Yosemite Glacier. The opinion has been ad- 

 vanced that the lesser dimensions of the Hetch Hetchy Val- 

 ley bespeak erosion by a less powerful ice stream than that 

 which enlarged the Yosemite Valley. This is utterly re- 

 futed by the morainal record. The Hetch Hetchy Valley, it 

 appears, was fairly smothered under ice at times when the 

 Yosemite was but half filled. That it was not enlarged pro- 

 portionately to the volume of its glacier is to be ascribed 

 primarily to the exceeding resistance of its massive rocks. 

 The lesson is that in a region of massive granites such as the 

 Sierra Nevada, the size of a valley cannot safely be taken as 

 an index of the magnitude of the glacier that passed through it. 



