I found a fascinating little essay on the close link between the California Gold Rush and Mercury http://limitedinc.blogspot.com/2006/08/solnit.html discussing how the California Gold rush depended on a lesser known "Mecury Rush" near San Jose.
What's fascinating is how the mercury contamination is continung to this day:
Originally posted by Limited, Inc
I have to stop eating so much fish. Scary stuff.