176 



GUIDEBOOK OF THE WESTER!^ UlSTITED STATES. 



Imlay, a town of recent establishment^ is a railroad division point. 

 With its growth Mill City has declmed. Due sonth of Imlay is the 



Imlay. 



Elevation 4,197 feet. 

 Population 326.* • 

 Omaha 1,398 miles. 



north end of the West Humboldt Range, the north- 

 ern and higher part of which is also known as the Star 

 Peak Kange. Here is an excellent example of the 

 characteristically abrupt termination of the basin 

 ranges. The smooth, gradual slope of the alluvial 

 plain sweeps up to the very foot of the mountain front, and foothills 

 proper are lacking. 



South of Imlay a fau-ly abundant supply of good water is found 

 in springs near the base of the mountains and piped do^vn to the rail- 

 road. The natural flow from such springs never reaches far beyond 

 the base of the mountain, as the water rapidl}^ sinks in the loose soil 

 or rocky detritus of the piedmont plains. From Imlay to Humboldt 

 the raihoad cuxves around the north end of the Star Peak Range and 

 then, turning almost due south, keeps the west side of this rugged 

 mountai^i mass in fuU view. (See PI. XXXVI, A,) 



At Humboldt station is Humboldt House, an old hotel building 

 that was formerly a meal station on the railroad. A good supply of 



Humboldt. 



Elevation 4,23S feet. 

 Omaha 1,405 miles. 



pure water is brought down in pipes from the moun- 

 tains southwest of Humboldt, making the place an 

 oasis, with trees and green fields. The Ruby quick- 

 silver mine is in Eldorado Canyon, about 8 miles south- 



east of Humboldt. 



The Star Peak Range ^ is rather regular in outline 

 75 miles loner. 



On the south it is separated by a low^ pass (Cole 



* The Star Peak Range is made up of 

 great masses of Triassic rocks belonging 

 to two formations^ the Star Peak and the 

 Koipato. The Star Peak formation, the 

 younger of the two, occupies mainly the 

 northern half of the Star Peak Range and 

 has an estimated thickness of 10,000 feet. 

 It ia made up of quartzite, limestone, and 



slates, among which have been found fos- 

 sil remains of both Middle and Upper 

 Triassic vertebrate and inAertebrate ani- 

 mals. These rocks are overlain con- 

 formably by limestone and dark slates 

 containing Jurassic fossils. The underly- 

 ing Koipato rocks, so called from the In- 

 dian name of the west Humboldt Range, 

 form a considerable part of the southern 

 half of the Star Peak Range. The Koipato 

 formation was originally described as 

 couijisting chiefly of beds of quartzite 



by inter- 

 limestone, quartzite, 



erlain 



and ''felsitic porphyroids,"and as hav- 

 ing an estimated thickness of 6,000 feet. 

 According to later determinations, how- 

 ever, the Koipato consists chiefly of lava 

 flows (Ayolite) with subordinate non- 

 volcanic sediments, including limestones. 

 Much of the rock: originally taken to be 

 quartzite is actiuilly rhyolite. 



The Triassic slates and limestones oi 

 the West Humboldt Range are noted for 

 the abundant and well-preser\-ed fossils 

 found in them. These comprise skele- 

 tons of ichthyosaurs ("fish lizards/* ex- 

 tinct marine animals of large size), spines 

 and teeth of extinct tj-pes of sharks, and 

 numbexs of the coiled shells known as 

 ammonites. 



On the lower slopes of the Star Peak 

 Range are considerable bodies of Tertiary 

 rhyolite and basalt, with which occur re- 

 lated beds cf tuffs or other water-laid 

 sediments of about the same ase. 



