I recently tracked down a miner from Treskillard who emigrated and worked for a time in the Tramway mine, Butte, Montana. In looking for some info on the mine I came across this site. Don't know if it's been posted before but some interesting photos. Of course many Cornish went to Butte as we know.
http://www.miningartifacts.org/MontanaMines.html
The past is a foreign country: they do things differently there.