Veering from the high to the low, there’s the Berkeley Pit, the enormous open-pit copper mine just next to uptown Butte. Because of the high costs of hard-rock underground mining, in 1955 Anaconda began stripping low-grade copper ore from the surface. Eventually the Berkeley Pit reached a depth of 1,800 feet; the gulf from side to side is more than one mile across.

Mining has ceased here, and today the pit is filling with water—Montana’s deepest body of water. It is also probably its most toxic water, percolating up as it does through abandoned mine shafts. The poisonous water is a threat to passing waterfowl: A flock of endangered trumpeter swans died in the lake one spring. If left undrained, it’s only a matter of time before the rising water will enter the Butte water table, causing further havoc.

A viewing stand (200 Shields St., 406/723-3177, March–Nov., $2) allows you to look down into the Berkeley Pit and its eerily green water (from dissolved copper and mineral salts).