Into the Breach Craft Unseen

MERCURY: New Almaden Quicksilver Mine, San José, CA

Photos: Andrew Alden/, Matthew Lee High/, Joan Pendleton/

Cartographer's note: I did not know about this mine or the mining town that grew up around it. I have heard about high levels of mercury in the groundwater for some time but never made the connection to how mercury is extracted or what happens when it is released into nature. New Almaden is now parkland with a historic building converted to a mining museum.

"The value of the production from all the lands exploited for mineral products in California in 1965 averaged $10,000 per acre. For more restricted areas high yields have been obtained over a period of many years; for example, in the New Almaden mercury district, less than 1,000 acres of mineralized ground has 10 yielded nearly $100,000,000, or roughly $100,000 per acre."1

"Long before the successful mining operations of New Almaden in the 1800s, local Ohlone Indians used the area as a source of the deep red mercury-bearing rock, cinnabar. The Ohlone painted their bodies a bright red with the cinnabar and also found it an important item to trade. Cinnabar expeditions came from as far away as Walla Walla, Washington to the New Almaden area to trade or fight for the prized resource."2

"The most dangerous form of mercury is not liquid mercury, the well-known quicksilver valued by miners, but a compound called methylmercury. When mercury sits in the sediments of oxygen-poor waters of lakes and wetlands, bacteria produce this potent neurotoxin from the mercury. It is taken up by algae, then it concentrates as it moves from algae, to zooplankton, to prey fish, to predator fish, and finally to humans. To protect the public from the dangers of eating contaminated fish, warning signs near local ponds and reservoirs instruct anglers not to eat their catch."3

1 Edgar H. Bailey and Deborah R. Harden. "Map Showing Mineral Resources of the San Francisco San Francisco Bay Region, California - Present Available and Planning for the Future." Miscellaneous Investigations Series, United States Geological Survey, 1975.
2 “New Almaden Mining Historic District.” Accessed February 28, 2022.
3 Oakland Museum of California. “The Legacy of the Mercury Mines.” Accessed February 28, 2022.