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



planes and with but very slight tilting. The relatively depressed blocks, 

 which have formed the lateral valleys, also settled, with some slight 

 breaking into secondary blocks, two of the more elevated of which, in the 

 western intermontane valley, now rise as low basalt- covered bedrock 

 ridges above the lake beds and alluvium of the valley bottom. 



Physiographic tests — Form and structure. — If the above conclusions are 

 true, the East range must stand the test of the physiographic criteria of 

 faulting. The East or Table Mountain range presents a unity such as 

 we have described for the other ranges. It rises sharply and distinctly 

 from the surrounding flat valleys, with a simple marginal trace and 

 ridge line. These features are distinctly unrelated to the structure of 

 the bedrock series. The front of the range where met by the detailed 

 section runs 30 or 40 degrees east of north, the slates 5 degrees west of 

 north. Not quite half way up the range the rocks swing around and 

 run northwest and southeast, dipping southwest. This attitude was 

 traced across several canyons (perhaps a mile or more). These and 

 other discordances and variations are not represented in the topography 

 at all. A glance at the general features of the Fortieth Parallel Survey 

 atlas shows distinctly the lack of relationship between structures and 

 either margin or ridge line. 



Erosion features. — Where examined, the East range shows almost no 

 tendency toward the formation of subsequent drainage features. The 

 canyons head back at a high angle to the front of the range, with very 

 little cUrvature or sinuosity, toward the crest. Throughout their courses 

 they pass parallel or perpendicular or at any other angle to the strike of 

 the rocks indifferently. As in the Star Peak range, this character of 

 drainage, as compared with the incipient subsequent character in the 

 Humboldt Lake range, is probably due to the altitude of the range — 

 that is, to the magnitude of the uplift — the continued elevation prevent- 

 ing the drainage from becoming adjusted to the structural and lithologic 

 conditions of the bedrock. 



No bay- or gulf-like extensions of the valley floor are yet indicated in 

 barest infancy, and no in tramontane valleys, subsequent and low, are 

 to be found. Everything points to recent uplift, the erosion forms being 

 not only unadjusted, but in their youth from source to mouth. Where 

 crossed by the detailed section one of the larger channels leaves the 

 mountains 650 feet above the valley floor, and reaches the valley along 

 a cone over 14,000 feet in radius. It is highly improbable that erosion 

 sufficient to have carved out the surrounding valleys could leave the 

 range in such a youthful condition in its physiographic cycle. 



The flat table tops unbroken except by faulting, and the basalt dip- 

 ping down underneath the valley on the east side of the first western 



