Here is an excerpt from PitWatch.org (Check them out)
"The Berkeley Pit is a former open pit copper mine in Butte, Montana. Approximately 320 million tons of ore and over 700 million tons of waste rock were mined from the Butte Hill. Put another way, the Berkeley Pit and Butte mines produced enough copper to pave a four-lane highway four inches thick from Butte to Salt Lake City and 30 miles beyond. Today, the Pit is filling with highly contaminated water, and managed as a federal Superfund environmental cleanup site."