QUATERNARY PERIOD ON THE WESTERN SIDE OF THE CONTINENT. 567 



a complicated, deeply-dissected outline, with the numerous mountain- 

 ridges of the Basin region forming high islands and promontories. So 

 far as known, it had no outlet. As the Quaternary period passed away, 

 these great lakes dried aivay more and more. The residues of the one 

 are Great Salt Lake, Utah Lake, and Sevier Lake ; of the other, Pyra- 

 mid, Winnemucca, Humboldt, Carson, Walker, and Soda Lakes. If in 

 the East, the Quaternary lakes mostly drained away, in the West they 

 mostly dried away to their present condition. The map (Fig. 935) 

 gives outlines of these two great lakes and their present residues. 



In both of these great lakes, according to Gilbert and Russell, there 

 are abundant evidences of two flooded periods separated by a period 

 of complete desiccation. If the flooded periods correspond with peri- 

 ods of great development of the ice-sheet, as seems probable, Ave have 

 here also — as in the eastern part of the continent — two Glacial periods 

 separated by an interglacial. 



River-Beds. — Old river-beds are found in many countries,, and es- 

 pecially in the Drift region of the Eastern portion of our continent 

 (p. 557), but those of California are peculiar. In the East and else- 

 where, the Tertiary river-beds are in the same places, but Mow the 

 present river-beds ; in California they are far above, and in many cases 



Fig. 936.— Map of a portion of the Eegion of the Deep Placers of the Yuha Kiver: The black, lava- 

 flows; the dotted spaces, gravel (after Whitney). 



in different places — i. e., the rivers have been displaced from their 

 former beds and cut much deeper. In map (Fig. 936) we give a portion 



