70 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [bull. 213. 
and hydraulic operation, and during the last } T ears it has probably 
been from $20,000 to $40,000. Very similar were the conditions 
during later years in Florence, which Camp has been described in a 
previous report." The total output of Florence was, however, consid- 
erably larger than that of Elk City. 
Florence, Warren, and' Elk City are situated in Idaho County. 
According to the Mint reports, this county has, since 1880, produced 
an average of $200,000 per annum, or a total of about $6,000,000. 
Something like one-half of this amount probably comes from Warren, 
leaving $3,000,000 as the production of Florence and Elk City for the 
last twenty years. Pierce is located in Shoshone County. 
It is a somewhat surprising fact that in spite of the recent activity 
in prospecting and working quartz veins the production of Idaho 
County should have decreased during the last few years. The Mint 
reports give for Idaho County the following amounts: 
Precious-metal production of I<l<i/i<> Oounty, Idaho, 1895-1901. 
1895 . . $243, 700 
1896 . . 155, 350 
L897 ---- 230,500 
1898 ... 203,500 
1899 .. 166,000 
1900. ... 152,000 
1901.. 161,500 
GEOLOGICAL RELATIONS. 
Nearly all the vein deposits occur in granite or gneiss, and the pre- 
vailing strike of the veins seems to be in an east- west direction. The 
granite, which is the prevailing rock, represents the northward con- 
tinuation of the greal area of central Idaho north of Snake River. 
Gold-bearing veins occur both within this area and along its contacts 
with the surrounding, older, sedimentary rocks. But for a long dis- 
tance north and south of Salmon River the central large granite areas 
seem comparatively barren, contain ng few deposits, with the excep- 
tion of the Warren camp. 
Within the region here discussed a peculiar relation obtains: The 
large central areas of granite, whether sheared, as along the eastern 
margin of the Bitterroot Mountains, or massive, as is usually the case, 
seem conspicuously barren of deposits. The vein systems appear in 
or close to the four smaller areas of sedimentary or metamorphic rocks 
which are found at the perip ery of the great central granite area. 
This is the case in the quartzitic series of Lolo Fork, in the quartzites, 
slates, and gneisses of the upper South Fork of the Bitterroot, and in 
the old gneiss areas of Elk City and Pierce. While the age of the 
quartz veins is not established beyond doubt, it is probable that they 
were formed during the later part of the Mesozoic. 
"Lindgren, W., The gold and silver veins of Silver City, De Lamar, and other mining dis- 
tricts in Idaho: Twentieth Ann. Rept. U. S. Geol. Survey, Pt. Ill, p. £*1 
