Yosemite National Park 197 



high Sierra region. From these cirques came the smaller glaciers 

 which coalesced with others and formed the great trunk gla- 

 ciers which bore down the Sierra slope, following naturally the 

 lines of least resistance and descending the chasms which had 

 already been formed by the streams. 



Snow-ice formed a mantle along the crest of the High Sierra 

 from Mount Lyell to Mount Whitney, a distance of fully 100 

 miles, and having a width of 20 to 30 miles. Only the major 

 peaks and crests stood out above the ice flood like dark rocky 

 islands above a dazzling sea of ice. It covered all those parts of 

 the High Sierra which are drained by the San Joaquin, Kings, 

 Kaweah, and Kern rivers. At first only drifts and fields of 

 compacted snow survived from year to year. By degrees these 

 perpetual bodies of snow-ice or neve attained sufficient depth 

 so that under the influence of gravity they acquired a slow 

 motion forward, and pushed in tongue-like ice streams or gla- 

 ciers down valleys that had been cut by streams. Each ice- 

 stream tended to follow a pre-glacial stream channel. Where 

 such pre-glacial valleys united the glaciers merged together 

 forming wider and deeper ice-streams. Down the Sierra slope 

 these ice-streams coalesced to form trunk glaciers that moved 

 down the main Sierra canyons. Thus at length every valley in 

 the High Sierra came to hold an ice-stream. During the time 

 when glaciation was at its height the snows were so abundant 

 that the trunk glaciers, though thousands of feet in thickness, 

 could not carry away the snow-ice from the gathering grounds 

 of the High Sierra as fast as it accumulated. Branch glaciers 

 overflowed and submerged the low divides between them so as 

 to form broad fields of snow-ice scores of miles in extent. 



Extent of Glacier Ice 



Thus a vast field of snow-ice came to cover the upland of 

 the Yosemite region. The ice mantle extended for many miles 

 down the western slope from the high Sierra crest, but did not 

 reach to the foot of the range slope due to melting at the lower 



