682 DESOEIPTIVE GEOLOGY. 



into the range away from the granites. Higher tip the ridge, and 2 or 3 

 miles to the southward, the heds in the region of a large trachyte outburst 

 dip eastward. North of Gold Run Creek, the same beds are structurally of 

 little importance, and are for the most part concealed beneath extensive 

 flows of rhy elite, which have broken through them, and now terminate the 

 range to the northward. The only mining operations in the range are cen- 

 tred in the region of Gold Run Creek, along a prominent quartz-vein, in the 

 siliceous slates, which is said to have been traced for more than 3 miles. It 

 dips to the westward at an angle of 30°, and, where developed, shows well- 

 defined foot and hanging-walls, with marked uniformity of strike and dip. 

 The ore consists mainly of oxidized products, with but few well-defined 

 mineral species. A short description of the mining operations in the dis- 

 trict will be found in " Mining Industry", Vol. Ill of this series. 



At the extreme northwestern end of the range, due east from Winne- 

 mucca Station, the Triassic beds again come up from beneath the rhyolitic 

 rocks, and at White's Canon consist of limestones, with interstratified beds 

 of calcareous shales and some white quartzites, having a strike of north 

 30° east, and a dip of 45° to the eastward. In Sonoma Canon, very similar 

 beds of slate, with bluish- white quartzites and siliceous felsites, are exposed, 

 striking north 15° west, and dipping 35° to 40° to the westward, but 

 increasing in the angle of inclination toward the interior of the range, until 

 just above the forks of the canon they stand nearly vertical. Above the 

 junction of the two forks, the beds show considerable displacement, with 

 an obscure structure, and have been fractured by intrusions of rhyolite. 

 Thi-s latter rock presents an ash-gray color and microfelsitic groundmass, 

 characterized by translucent quartz-grains, showing but little mica or well- 

 developed feldspars. 



In the foot-hills just north of Sonoma Canon, the strata, w*hich con- 

 sist of dark-blue heavily-bedded. limestone underlaid by fine-grained quartz- 

 ite, are seen dipping eastward into the range, with a strike of north 8° to 

 10° west, and apparently forming a synclinal fold with the ca,non rocks. 

 In this limestone was obtained the only fossil found in the range, Halobia 

 duhia, a characteristic Triassic species, abundant in the Star Peak beds in 

 the West Humboldt Range. Below Sonoma and Clear Creeks, the ridge 



