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University of California. 



[Vol. 3. 



gebmorphy would at least have approximated to maturity, though 

 the latter might not have been so prouounced as in the region 

 where less work had to be done. (2) The second modifying 

 consideration is that, during the Sierran glacial period, the 

 Toowa Valley country continued under the dominion of atmos- 

 pheric and steam erosion, and so advanced in its geomorphie 

 evolution on the old lines, while glacial forces were at work 

 immediately to the north. This advance is of course propor- 

 tionate to the length of time represented by the glacial occupation 

 of the High Mountain Zone in the northern part of the basin. 

 This period is believed by the writer to have been brief as com- 

 pared with the whole time concerned in the evolution of Toowa 

 Valley. The volcanoes and lava flows which encumber and 

 obstruct Toowa Valley are probably preglacial in age, and the 

 extent to which they have been modified by atmospheric and 

 stream agencies is comparatively slight. (3) The third consider- 

 ation is that in Sierran post-glacial time the geomorphie evolution 

 of the Toowa Valley borders may have advanced again on the old 

 lines, whereas, since the evacuation of the northern part of the 

 region by the glaciers, atmospheric and stream agencies have had 

 to adjust themselves to entirely new conditions. The modifica- 

 tion due to this cause is, however, practically negligible, since in 

 the glaciated portion of the region, the glaciated surfaces are still 

 to a large extent intact in the condition in which the ice left 

 them. 



The general result is that the mature geomorphy of the 

 country around Toowa Valley was in its essential features 

 attained in time anterior to the Sierran glacial period, and rep- 

 resents very fairly the general character of the upper slopes of 

 the entire Upper Kern Basin up to the advent of glacial condi- 

 tions; and that we thus have, in a comparison of the glaciated 

 and unglaciated portions of the High Mountain Zone, an 

 approximate measure of the geomorphie revolution which has 

 been effected in the former by ice action. 



Another point of difference between Toowa Valley and Cha- 

 goopa Plateau is that the latter is dissected by the great canon 

 of the Kern to a depth of about 2,500 feet; and the tributary 

 streams of the Kern which traverse the plateau hive trenched it 



