Leviathan Mine, California
A classic case of acid-mine drainage. It's a US EPA Superfund site. The ponds are to keep the leachate from flowing into the Carson River.
Leviathan Mine, CA
An abandoned sulfur mine in California, just over the state line from Nevada. It's now a Superfund site due to sulfuric acid formed by the oxidizing sulfur. Not only has the acid itself had a deleterious effect on draining into the local streams, but the acidity also leaches metals into solution up to toxic levels. This is a textbook case of "acid mine drainage" from abandoned mines.