Yosemite National Park. 203 



The glacial features that have been considered in the fore- 

 going pages relate to the latest epoch of glaciation in the 

 Yosemite region, the Wisconsin. This was the lesser of two, 

 possibly three, glacial invasions that have ploughed down the 

 Yosemite Valley. Evidences of an earlier and more extensive 

 glaciation occur on the higher slopes of the valley and adjacent 

 mountains. The later Yosemite Glacier extended down the 

 Yosemite Valley as far as the Bridalveil Meadow. The earlier 

 Yosemite Glacier ploughed down the valley of the Merced River 

 as far as the vicinity of El Portal, and it is spoken of as the 

 El Portal stage of glaciation. Scattered boulders that are for- 

 eign to the Yosemite region and that have come from the 

 crest of the Sierra Range occur above the moraines that lie along 

 the sides of the Little Yosemite Valley. These boulders are all 

 rust stained and weathered to a depth ranging from an eighth 

 of an inch to half an inch. Many of them are so "rotten" that 

 they fall apart at a moderate blow of the hammer. Study of 

 these rocks and their occurrence high above the moraines that 

 have been noted leads to the conclusion that ice of a glacier at 

 a comparatively early date reached a level much higher than 

 that of the prominent moraines of the valley below. The high- 

 est of these old weathered moraines in which the boulders 

 referred to occur is more than 1,000 feet above the level of the 

 highest of the younger moraines which lie along the sides of the 

 Little Yosemite Valley. 



Depth of Ice of Earlier Glaciation 



The Cathedral Rocks bear on their summits and slopes 

 deposits of glacial boulders that give some idea of the depth 

 attained by the earlier Yosemite Glacier. So imposing are the 

 Cathedral Rocks when viewed from the floor of the Yosemite 

 Valley that it is difficult to imagine them as once having been 

 covered by the ice, yet the testimony of the boulders leaves no 

 doubt that they were. Even the highest of these boulders do 

 not mark the highest level reached by the ice flood. On the 



