340 G. D. LOUDERBACK — STRUCTURE OF THE HUMBOLDT REGION 



Since the Pleistocene there has been little change with the exception 

 of the desiccation. Some erosion has taken place, particularly in the 

 upper parts of the ranges, and the great alluvial cones have been brought 

 to their present condition. Faulting has taken place in very recent time 

 along the old lines, the scarps cutting lake features and cones, but only 

 of moderate magnitude — 25 to 50 feet or more. 



Comparison with the Sierra Nevada 



Anyone familiar with the geological history of the Sierra Nevada must 

 have been struck by its remarkable similarity to that of the Humboldt 

 mountains and vicinity. A brief chronology of each is given here for 

 comparison. Some events have to be stated in a general way to bring 

 out the analogy. 



SIERRA NEVADA HUMBOLDT REGION 



Triassic Marine deposits, including limestone. The same. 



Similar fossils in both regions. 



? ? Some volcanic activity. 



Interim Some disturbance before opening of The same. 



Jurassic. 



Jurassic Marine deposits, chiefly slates. . . . The same. 



Much volcanic activity No volcanic products noted. 



Interim Great deformation by folding The same. 



Granite intrusions The same (possibly, how- 

 ever, post-Triassic). 



Cretaceous. . . Erosion period The same. 



Drainage to the sea The same. 



Tertiary Completion of great erosion cycle with The same. 



production of low relief — partial 

 peneplanation. 



Great volcanic activity The same. 



Lake beds deposited The same. 



A certain amount of deformation in The same, 

 later Tertiary (Neocene). 

 Interim Upheaval by faulting and tilting be- 

 gun. 

 Pleistocene... (1) Period of erosion, probably with 

 continued uplift. 

 (2) Freshwater lakes at east base 



(Mono, etcetera). 

 Two periods of flooding, with inter- 

 mediate desiccation. 

 Glaciation at least partially coincident 

 with lake periods. 



The same. 



The same. 



Lake Lahontan. 



The same. 



Recent. 



Extensive desiccation of lake basins. 

 Faulting along old lines. 



Glaciation reported from 

 Star peak, but relationship 

 to lake not determined. 



The same. 



