There was a time when the mining town of Butte was one of the largest cities west of the Mississippi. In 1890 it had 80'00 inhabitants, making it the largest city between Minneapolis and San Francisco. Butte was the quintessential mining town, and while silver and gold were being mined over long periods of time, it was copper that really put Butte on the map. World War One (bullets!) and the development of electrical grids throughout the US and worldwide created an endless appetite for copper.
Butte, with its hundreds of miles of underground tunnels was producing just that: one ton out of three the US demanded came from Butte in the late 1800's and early 1900's. Toward the second half of the twentieth century, open traditional mining gave way to the less labor intensive pit mining.
Large scale copper production stopped in 1982 and as the pumps were stopped, reddish mineal-laced toxic groundwater rose to fill the shafts and a large part of the Berkley pit, creating what is now labelled a 'Superfund Site,' not just one but the largest of the recognized top hazardous sites of the US.
Butte, Mt. - The Faded Glory of a Formerly Grand City (Expo Focale 2011)