THE MINING DISTRICTS OF THE IDAHO BASIN AND THE 

 BOISE RIDGE, IDAHO, 1 



By WALDEMAR LINDGREN. 



CHAPTER I. 

 GENERAL TOPOGRAPHY AND GEOLOGY. 



GEOGRAPHICAL POSITION. 



The region shown in PI. LXXXVII includes a portion of the lower 

 Snake River Valley and the mountains adjacent on the northern side. 

 The total area is about 13,500 square miles. It embraces, besides a 

 part of the Snake River, almost the whole drainage of the Payette, 

 Boise, and Wood rivers, and, in the northeastern corner, a part of 

 that of the Salmon River. The irregular mountain complex within 

 the drainage of the Boise and the Payette rivers is designated the 

 "Boise Mountains; " along the parting between these rivers and the 

 Salmon River drainage rise a series of sharp peaks, usually referred 

 to as the " Sawtooth Range." The " Boise Ridge " extends from the 

 Boise to beyond the Payette just west of longitude 116, and attains 

 elevations of over 7,000 feet. The Idaho Basin is an interniontane 

 valley in the Boise Mountains south of latitude 44 and east of longi- 

 tude 116. 



The map shows the positions and names of the quadrangles repre- 

 sented by the topographic sheets issued by the United States Geolog- 

 ical Survey. It also shows, in a somewhat generalized way, the geology 

 of a part of the area. 



SNAKE RIVER VALLEY. 



The discussion of the geology of this district necessitates a short 

 reference to the large Snake River Valley and an abstract of previous 

 work relating to its remarkable geological features. The Snake River 

 Valley stretches across the whole width of southern Idaho in a broad 

 curve opening toward the north and having a radius of 160 miles. The 

 length of this valley from the base of the Tetons to Weiser, where the 

 river enters into a narrow canyon, is over 400 miles, while its width 



1 The field work upon which this report is based was done during the summer and fall of 1896 

 by the author, assisted by Dr. E. C. E. Lord. 



18 GEOL, PT 3 40 625 



