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



The summits of the range to the west of Lovelock are covered with 

 basalt, which slopes off in long, regular sheets. 



In general. — The Trinity mountains have not the homogeneity of the 

 other ranges discussed, and the movements that have affected them in 

 both their pre- and post-Tertiary-volcanic times seem to have been more 

 complex than for the other ranges. No attempt was made to decipher 

 the details of their history. 



Lone Mountain hills. — About 2 miles east of the base of the Trinity range 

 lies a short range of hills which in its relationships to the Trinity moun- 

 tains is similar to the valley hills before Table mountain. The detailed 

 section passes over the highest one, which is called Lone mountain. 

 This hill rises about 650 feet above the valley floor and is capped by 

 rhyolite. The rhyolite is underlain by tuff and this again by granite 

 and hornfels. The tuff and lava dip to the northeast and go down below 

 the valley floor, the even surface being broken only by the Lahontan 

 shore lines. Plate 19, figure 1, shows Lone mountain in the center, with 

 its associated hills passing off to the left. The distant high skylines at 

 right and left show the sloping basalt caps of the Trinity mountains. 



The granite is exposed at the left (south) end, rounded and hollowed 

 out by the action of the old lake's waves. This is much better seen in 

 plate 19, figure 2, the south end of Lone mountain. The tuff is rather 

 hidden by the talus. The northeastward slope of the rhyolite and the 

 manner in which it has been cut into by the breakers is well shown in 

 plate 20, figures 1 and 2. To the northeast of this last view the rhyolite 

 dips under the valley. A striking feature of Lone mountain is the plane 

 surface of the granite on which the tuffs were deposited. This is also 

 very evident in the Trinity Mountains foothills. 



No break occurs in the valley from Lone mountain to the basalt flats 

 at the base of the Humboldt mountains, 8 or 9 miles away. 



On the Fortieth Parallel Survey map a patch of basalt is represented 

 on the west side of Lone mountain in such a position that it must either 

 have been deposited before the rhyolite or since the period of deforma- 

 tion. A careful search was made for this basalt, but none could be found. 

 A black, hard, compact rock does occui there, but it is a highly meta- 

 morphosed rock into which the granite is intrusive. It will be described 

 later. 



Discussion of special Features of detailed Section 



method of preparing the section 



Sections across the Basin ranges, which have hitherto been published 

 in connection with discussions of the Basin Range type of structure, are 

 sketched to represent ideal conditions and are generally given with 



