902 W. LINDGREN—F. H. KNOWLTON 



The largest glaciers were found on the headwaters of the Yuba 

 and the American rivers. The lowest elevation at which glacial 

 traces have been found on the western slope is about 3500 feet. 

 The third period, the present, is marked by the disappearance of 

 the glaciers and by the continued formation of fluviatile 

 deposits in the Great Valley. 



It is not believed that, during the early Pleistocene any 

 marked orographic changes took place along the eastern base of 

 the Sierra. In very recent times — after the glaciation — a 

 renewed faulting is noticeable at many places, such as at Owen 

 and Mono lakes and near Genoa south of Carson, Nevada. At 

 the later place the displacement is about 40 feet. Very strong 

 springs, many of them hot, are located along the foot of the 

 scarp, which is extremely sharply marked. As at Mono Lake^ 

 the deepest depression — here the Carson River — closely hugs the 

 escarpment for considerable distance in spite of the active erosion 

 and the large amount of material transferred to the valley from 

 the escarpment. This appears to be a strong argument in favor 

 of the view that the eastern block — the Carson Valley — is 

 sinking, instead of the western block — the mountain scarp — 

 rising. 



The similarity of these conditions with those at the foot of 

 the Wasatch, so admirably described by Mr. G. K. Gilbert, cer- 

 tainly appears very striking. 



Recently Mr. F. L. Ransome has published an interesting 

 criticism of the theory of isostacy as applied to the interior valley 

 of California,^ in which he arrives at the conclusion that the facts 

 do not support the theory, in the case of the Great Valley, a 

 conclusion which appears well justified. Mr. Ransome's argu- 

 ment could, however, have been made much stronger. From 

 the above, it is clear, that there have been at least three impor- 

 tant transgressions separated by unconformities, representing 

 periods of erosion, since the end of the Cretaceous. The rivers 

 sometimes extended far into the valley, while at other times the 



^ I. C. Russell, U. S. G. S., 8th Rep., pp. 261-394. 

 »Univ. Calif., Bull. Dep. Geol., Vol. I, No. 14, pp. 371-428. 



