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



vium (that is, of buried and concealed rock) are represented as underlaid each by 

 a block at lower level, or by the subterranean continuance of one sloping ridge to 

 the next ; and the actual flexures or lines-of bedding have been omitted, and mono- 

 clinal lines substituted. They are intended to exhibit the supposed structure. 

 But until the stratigraphy of the ridges of the whole basin shall have been studied 

 and sections of them represented, and the relations of each ridge to those lying on 

 the same northward or northwestward line of strike shall have been thoroughly 

 investigated, general stratigraphic conclusions can not be safely drawn." 



It would seem, then, that what is most needed is more information 

 concerning the structural and other features of the individual ranges 

 and valleys of the Basin region as a basis for the more general conclu- 

 sions. In the present paper it is purposed to offer such information for 

 a limited district in northwestern Nevada, the central geographic feature 

 of which is the Humboldt Mountain range, and to draw from it conclu- 

 sions as to the orogenic history of the district. 



The Humboldt Lake Mountains 

 location and extent 



The Humboldt range of mountains (the Koipato or West Humboldt 

 range of the Fortieth Parallel Survey) lies in the western Basin region, 

 in northwestern Nevada, some few miles west of the 118th meridian. 

 As shown on accompanying map (plate 15), it. is divided transversely 

 into two parts, which are rather sharply separated by a considerable 

 depression. The northern part, which may be called the Star Peak 

 range,* runs almost due north and south for some 34 miles and reaches 

 an altitude of 9,925 feetf in Star peak, 5,663 feet above Humboldt sta- 

 tion. The southern part, which may be called the Humboldt Lake 

 range, runs approximately northeast and southwest for about 42 miles 

 and reaches the more moderate altitude of about 6,600 feet, or about 

 2,700 feet above the valley at Lovelock. The first part of the following 

 discussion will deal with the southern range only, unless otherwise dis- 

 tinctly stated. 



The rocks of the Humboldt Lake mountains fall naturally into two 

 groups, which may be called, following the nomenclature adopted by 

 the U. S. Geological Survey in the Sierra Nevada, the bedrock complex 

 and the superjacent series.]; These differ in age, origin, and structural 

 relationships. 



*See further on this point pp. 319 and 320. 



f According to topography of Fortieth Parallel Survey. 



% The word series as used in this paper has no special technical stratigraphic significance, but 

 applies merely to a succession of rock formations conveniently (and naturally) grouped together 

 for the purposes of description and discussion. Complex seems to be a rather strong term for the 

 bedrock of the Humboldt Lake range, but it seems desirable for purposes of comparison to use 

 this expression, and the older rocks form quite a complex in some of the neighboring ranges. 



