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



there has been no corrasion along the mountain flanks in post-basaltic 

 times. 



After the outpouring of the basalt and the upheaval of the mountains, 

 the first event of which we have evidence in the valleys is the formation 

 of alluvial cones, then the deposition of Lake Lahontan sediments, fol- 

 lowing which comes the desiccation of the basin and the further deposi- 

 tion of alluvium by the river or mountain streams. In other words, 

 after the deposition and deformation of the basalt the broad intermon- 

 tane valleys, far from showing great erosion, have been continuously up 

 to the present day basins of deposition. 



Evidence from the basalt is by no means so complete on the west base, 

 but the occurrence of even these smaller areas shows that no extensive 

 corrasion, such as would have cut out the west valley and have deter- 

 mined the west slope, can have taken place, and the fact is that the moun- 

 tain slope passes down below the west base basalts, and from this slope 

 the basalts extend west either at a low angle (south of the road) or hori- 

 zontally (north of the road) from a half to one mile. Evidently the 

 west slope was not determined by any post-basaltic corrasion. 



SUMMARY 



The writer has sought to present all the observed phenomena which 

 bear on the question of the origin of the Humboldt Lake range of the 

 Humboldt mountains. The characters of the orogenic movements have 

 been determined by the following relationships : 



1. The nature, attitude, and distribution of the volcanic series. 



2. The independence of structure on the one hand and range line and 

 front on the other. 



3. The general character of erosion forms. 



4. The special character of the mountain stream valleys. 



5. The relation of the basalt to erosion. 



All of these tests are in consonance with an origin by faulting ; none 

 of them are compatible with an anticlinal uplift and erosion. We may 

 conclude, therefore, that the territory now occupied by the Humboldt 

 Lake mountains, at some post- Jurassic time previous to the formation 

 of the volcanic series, was in a condition of verv low relief. After the 

 outpouring of the basalt this territory was relatively uplifted with respect 

 to the present valleys, with faulting along its west margin and tilting 

 toward the east, thus producing the Humboldt Lake Mountain range. 

 Since the inception of the orogenic movements, the relatively depressed 

 areas — the valleys — have been basins of deposition, and the mountain 



