Mercury Mining

Historical Essay

by David D. Schmidt, 2026

An excerpt from the book, San Francisco Bay Area: An Environmental History, by David D. Schmidt (Backcountry Press, 2025).

The "reduction works" at the Almaden Mercury Mines, where ore was heated to vaporize the mercury, then the vapors cooled and condensed to produce the liquid metal.

Photo: Alice Iola Hare, c. 1900. BANC PIC 1905.05025--PIC, Bancroft Library, University of California, Berkeley.

Since the Middle Ages, alchemists, scientists, and fortune seekers have known that mercury, also known as quicksilver, has a peculiar affinity to certain metals, including silver and gold: Whenever mercury touches these metals, it absorbs and dissolves, or “amalgamates” them. In the Sierra Foothills, after the ‘49ers cleaned out the visible gold nuggets, they needed mercury to mix with gold-bearing ore, sand and sediment, to extract the microscopic gold particles that remained. The mercury, having absorbed the gold, was then heated in furnaces to at least 674 degrees Fahrenheit, vaporizing the mercury and leaving behind the pure gold or silver.

The Gold Rush and the gold and silver mining booms in Nevada and other western states in the late 1800s created tremendous demand for mercury. Conveniently, the nation’s biggest mercury deposits were in Northern California. Nearly 90% of the total U.S. mercury production prior to 1950—over 100,000 tons—came from a 350-mile stretch of California’s Coast Ranges extending from southern Mendocino County, through the Bay Area, to Santa Barbara County. About 13,000 tons of this mercury was used in California gold mining; the rest was exported to other states and countries.

The mercury deposits resulted from ancient volcanic activity, evidenced today by hot springs and geysers. The Mayacamas Mountains, between the Napa and Sonoma Valleys, are an especially active geothermal region. In the late 1800s, this area had more than 100 mercury mines.

Much of the mercury mined in the Bay Area and used in Sierra gold mines more than a century ago ultimately returned to the region, moving downstream along with more than a billion cubic yards of sand and sediment dislodged by hydraulic mining. This mercury was at the bottom of Suisun, San Pablo, and San Francisco Bays in the 1900s, but streamed out the Golden Gate along with the sediment by 1998, reducing mercury contamination in the bay. Some of it is still in the Sierra Foothills, in the ruins of mines and ore-crushing mills, in abandoned hydraulic mine drainage tunnels, in streambeds, or lying at the bottom of riverbeds and reservoirs on the Yuba, Bear, American, and Sacramento Rivers. Mercury continues to enter the bay in polluted runoff from old mercury mine sites, but this has been reduced in recent years by erosion control efforts at the mine sites.

Mercury Mining, Health, and the Environment

The human nervous system is very sensitive to mercury. Exposure to high levels can cause death or permanent brain and kidney damage. In September 1998, a woman and her one-year-old boy in Fresno died from inhaling mercury vapors when she tried to melt gold jewelry on a kitchen stove. The gold was contaminated with mercury, which vaporized, poisoning them. Hatmakers in England in the 1800s who used mercury in their work suffered from brain damage, dementia and uncontrollable shaking, giving rise to the phrase, “mad as a hatter,” the basis for Lewis Carroll’s character the Mad Hatter in Alice in Wonderland.

Mercury’s effects on developing babies include brain damage, mental retardation, blindness, seizures, and an inability to speak. Very young children are more sensitive than adults, but no one is immune. At the New Almaden Mine, before ventilation and improved safety procedures were introduced in 1863, an average of four workers died of mercury poisoning each year. These workers had to shovel hot, spent ore from the furnaces, with mercury vapors still rising from it. Each worker was required to do this only one week in every four, since more than that would quickly make them sick. In Spain's 2000-year-old Almaden Mines (for which the New Almaden was named) convicts were traditionally employed, because their labor was cheap, and their lives were expendable. At New Almaden, even after 1863, workers at the furnaces suffered from a "very pernicious effect upon the nervous system," which caused "palsy, vertigo, and other disorders of the brain."

Mercury harms fish, wildlife, and people in two ways: First, if it is ingested or inhaled, even small amounts can be fatal. Signs of mercury poisoning include nausea, vomiting, diarrhea, increases in blood pressure or heart rate, skin rashes, and eye irritation. Recreational gold miners who collect mercury from Sierra riverbeds and old mine sites, then heat the mercury to vaporize it and collect the gold, put themselves in grave danger.

Second, mercury that washes into waterways bioaccumulates. While pure mercury can’t dissolve in water, sulfate-reducing bacteria in the sediments of lakes and streams transform it into methyl mercury, which does dissolve. According to UC Davis aquatic ecologist Darrell Slotton, an expert on mercury bioaccumulation, mercury’s health impacts in California would be much worse if not for the alkalinity of the state’s lakes and streams, which slows the methylation process.

Mercury at the bottom of Tomales, Suisun, San Pablo, and San Francisco Bays moves up the food chain into the tissues of resident fish, such as sharks and striped bass—and people who routinely eat them. The state Office of Environmental Health Hazard Assessment (OEHHA) warns people to limit their consumption of these bay-caught fish to no more than two meals per month, and none at all for small children and women in their child-bearing years.

These warnings, called fish advisories, are posted on fishing piers along the bay’s shorelines, as well as the OEHHA website. The advisories are also included in the fishing regulation booklets people receive when they buy fishing licenses. In 2024, fish advisories for mercury and other toxic chemicals were also posted for the following Bay Area reservoirs and waterways: Sonoma, Berryessa, Soulajoule, Nicasio, Bon Tempe, Herman, San Pablo, Lafayette, Chabot, Temescal, Del Valle, Shadow Cliffs, Almaden, Stevens Creek, Lexington, Calero, Coyote and Anderson; plus Vasona Lake and Camden Ponds, Guadalupe River, Alamitos Creek, San Francisco Bay, Tomales Bay, Laguna de Santa Rosa, San Francisco’s Lake Merced, Richmond’s Lauritzen Channel, and Pinto Lake near Watsonville.

Mercury mining also had indirect impacts. The furnaces at mercury mines required a steady supply of fuel, which the mines procured in the late 1800s by chopping down nearby oak woodlands. While most of these oaks have since grown back, furnace sites may still be contaminated with mercury. Most of the mercury mines in the Bay Area in the mid-1800s through the 1920s were underground mines, which left the land surface largely intact. However, these mines left behind piles of spent ore, still containing some residual mercury. Later, from the 1930s to the 1960s, miners used bulldozers, cutting away hillsides to remove the ore. Every rainy season washed more of this spent ore (tailings) into nearby streams, rivers, and reservoirs, where bacteria transform insoluble pure mercury into more dangerous methyl mercury.

Old buildings, furnaces, and tunnels that still remain at mine sites should be considered extremely hazardous. DO NOT ENTER THEM! In addition to the dangers of mercury poisoning, ALL old mines pose serious risks of injury and death from falling through rotting woodwork or down mineshafts, tunnel cave-ins, and asphyxiation in tunnels where oxygen is depleted.

How Quicksilver Got Its Name; How It Was Mined, Refined, and Used

Mercury was known in past centuries as quicksilver, an Old English translation of the earlier Latin ‘vivum argentum,’ meaning ‘living silver.’ In archaic English, ‘quick’ meant ‘alive,’ as in ‘the quick and the dead.’ Pure mercury resembles molten silver, but is liquid at room temperature. Mercury appeared to the ancients to be living because drops of it consolidate into liquid “slugs” that quiver when touched.

Most mercury deposits in the Bay Area were locked within cinnabar, a reddish mineral. Miners dug out cinnabar, then heated it in furnaces until the mercury vaporized. The highly toxic mercury vapors were then cooled by passing them through a series of pipes until they condensed into pure liquid mercury, which was then collected, drop by drop, the same way whiskey is distilled. The mercury was stored in cast iron bottles known as flasks, each made to hold a standard 76 pounds of the liquid metal.

At California’s gold mines, mercury was poured onto trays filled with pulverized ore, or onto wooden sluiceways where a slurry of water, sand and gravel would be directed. The mercury would absorb the gold, but not the other materials. The mercury was then collected and heated in a furnace until it vaporized, leaving the pure gold. The vapors would pass through cooling pipes and condense back into pure liquid mercury.

Ideally, the mercury could be collected this way and used again. In practice, several hundred pounds of mercury per year would escape from these sluiceways, flowing downstream into rivers, and ultimately the bay and Delta. Mercury could also be lost through leaks or careless handling. In addition, some of the toxic vapor would escape out the furnace’s smokestack, and settle onto the surrounding landscape, where winter runoff carried it into streams and rivers.

The prices and production of mercury in the mid-1800s through the mid-1900s fluctuated wildly as gold and silver mines boomed and busted throughout the West, and the world. When gold and silver mining decreased, mercury prices dropped, making many mines unprofitable, and causing owners to shut them down temporarily. A gold or silver strike anywhere in the world was good news for mercury mine owners, for it would drive prices up, putting them back in business.

California’s mercury production peaked in 1877, when mines produced 3,060 tons. After hydraulic gold mining in the Sierra was restricted by Judge Lorenzo Sawyer’s 1884 decision in Woodruff v. North Bloomfield Gravel Mining Co., most hydraulic mines in the Sierra shut down. Mercury prices and production dropped immediately. The state’s mercury production never again topped 1,300 tons.

By the early 1900s, gold mines began using a different process to extract gold from ore, with cyanide (though mercury was still used in dredging Sacramento Valley flood plains for gold as late as the 1960s). Mercury prices dropped further; most mercury mines shut down. In 1913, only 16 reported any production. In 1914, California produced only 432 tons of mercury, the lowest amount in 54 years.

The outbreak of World War I revived mercury mines everywhere. In fact, wars anywhere in the world from the late 1800s through the 1950s brought increased demand and higher prices, since mercury compounds called mercuric fulminates were used in detonators on bombs and artillery shells. Mercuric fulminates explode when they hit a hard surface, triggering the bomb’s main explosive. As the war dragged on, mercury demand surged. Prices shot up sixfold between January 1915 and February 1916.

Bay Area mercury mining dropped off sharply after the war, then boomed again during World War II. In the 1940s, California mines supplied more than 70% of the nation’s mercury production. Again, after the war, production plummeted, partly because the U. S. Department of Defense stopped buying it in 1944, but also as a result of competition from cheaper mercury from Europe. By 1950, only one major U. S. mine, the Mount Jackson in Sonoma County, was still operating. Prices bottomed out at $70 per flask (about $1 per pound) in June 1950.

Mercury prices increased due to the Korean War, hitting $227 per flask by January 1951, but it was not enough to reopen more than a few Bay Area mines. The richest deposits had been depleted by a century of mining. In 1950-55, California’s mercury mines produced an average of only 288 tons per year, less than a fifth of nationwide consumption.

By this time, mercury had other uses, including batteries and electric switches (33%), industrial and control instruments (barometers, thermometers, etc., 22%), agriculture (in fungicides to treat seeds, 18%), dentistry (tooth fillings, 5%), electrolytic cells (to make chlorine, etc., 5%), pharmaceuticals (4%), laboratory uses (3%), catalysts (1%), and antifouling paint (on ships) (1%). Mining (0.5%) and munitions (0.25%) accounted for less than 1%.

In the 1950s, weapons designers developed new bombs that no longer needed mercury to detonate. Mining in the Bay Area continued sporadically through the 1960s, because Department of Defense purchases kept prices relatively high. But in 1970, the Pentagon took mercury off its list of strategically important minerals, and stopped buying for good. Prices plummeted. The federal government had a stockpile of 4,400 metric tons of mercury, but nobody wanted it, now that its toxic effects were known, and alternatives were available for most uses.

The last recorded mercury mining in the Bay Area took place in 1976 at the New Almaden Mines, right where it had begun 130 years earlier.

Lessons Learned

California’s mercury mining boom peaked in the early 1880s, but its toxic legacies remain. Mercury from the Bay Region's mines has been dispersed over thousands of square miles of land and waterways. Most of it cannot be collected or removed. The best that can be done is to identify mercury hot spots remaining at mine sites, remove the mercury there, and control soil erosion to prevent mercury-bearing ore and waste from getting into waterways.

In 2004, the San Francisco Bay Regional Water Quality Control Board (RWQCB) approved a $2.6 billion plan to prevent mercury from getting into the Bay—about half the estimated value of all mercury ever mined in the Bay Area. The New Almaden Mine's current owner – Santa Clara County—bears the largest share, since it is legally responsible for the largest source of mercury reaching the Bay. The former owners went bankrupt long ago.

The costly, toxic legacy of mercury mining is a reminder that the best way to protect the environment is to prevent pollution from occurring in the first place.

The New Almaden Quicksilver Mine

Immortalized in Wallace Stegner’s 1971 Pulitzer Prize-winning historical novel, Angle of Repose, the New Almaden Mine produced more than 45,000 tons of mercury by 1976—about a third of the entire nation’s production since 1850. In its peak years in the late 1800s, the mine employed 2,500 people—10% of Santa Clara County's population at the time. A thousand people worked underground, toiling through 11-hour shifts six days a week.

The New Almaden Mercury Furnace in 2000.

Photo: David D. Schmidt

New Almaden’s mercury, crucial to extracting gold and silver from mines in California and Nevada from 1848 to 1900, fueled the growth of San Francisco and Sacramento; Carson City and Virginia City in Nevada, and a host of other mining boom towns across the West. But it also left behind mercury contamination. The U.S. Environmental Protection Agency (EPA) estimates that 7,500 TONS of mercury polluted Nevada’s Carson River drainage alone.

The first miners at New Almaden were Native Americans who dug a cave into a hillside to get at the reddish, mercury-bearing cinnabar ore they used as a pigment for body-painting. In 1824 Luis Chaboya, a Mexican settler, believing this ore to contain silver, began digging it out. He procured from Mission San Luis Obispo an iron flask containing pure mercury, and mixed it with the crushed ore. He then collected the mercury (which would have absorbed any silver particles), and heated it until it evaporated, which would leave pure silver, if there was any. There wasn’t, so he abandoned the effort, missing his chance for fabulous wealth.

In 1845 Andres Castillero, a Mexican Army officer passing through the Bay Area on his way to Sutter's Fort in present-day Sacramento, made an official request at Mission Santa Clara to claim the mine, which he thought contained silver and gold. On his return trip, on December 3, 1845, he stopped again at Mission Santa Clara and sprinkled bits of the ore on hot coals. Over the coals he placed an inverted bowl. The fumes condensed on its surface, and beads of silvery liquid metal collected on the downward edge. He had proved the ore contained mercury. Still believing that it also contained silver and gold, he was awarded rights to the claim by Mexican Governor Antonio Maria Pico.

Castillero formed a mining company and hired William Chard of New York to run it. When Chard and Castillero dug deeper into the cave, they uncovered the skeletons of several Ohlone people who had been crushed centuries earlier when the cave partially collapsed. Chard used whalers' 3-foot-diameter cast-iron blubber-boiling pots to recover the mercury, placing them upside down over piles of ore and building fires on top of the ore, in a larger-scale version of Castillero's earlier experiment. Beads of liquid mercury dripped down to the edges of the pots, and Chard recovered 2,000 pounds of it.

Meanwhile, Castillero returned to Mexico City to secure financing to modernize the operation. In return for financial backing, he granted a 16-year lease on the mine to Barron, Forbes, and Co., an English banking firm in Tepic, Mexico. Company owner Alexander Forbes set out from Mexico with miners, money, and materials to start large-scale production.

The Mexican miners dug underground passageways, expanding them into larger chambers when they found cinnabar deposits. Wood-burning furnaces and condensing pipes replaced the blubber pots. In 1850, the first year production was recorded, New Almaden produced 7,723 flasks of mercury—nearly 300 tons. The following year, spurred on by demand from California's gold mines, production surged to more than 1,000 tons.

In the 1850s and 1860s, mercury mining was Santa Clara County's most lucrative industry, far outpacing agriculture. By the mid-1850s, New Almaden had a complex of underground mines, a town, furnaces and other processing facilities, all on land claims totaling about 14 square miles. Oak and madrone trees from miles around were cut for firewood to feed the furnaces.

After California became a state in 1850, Congress created a Board of Land Commissioners to settle ownership disputes resulting from American newcomers’ attempts to cheat Mexicans out of their land. A group of schemers organized as the Quicksilver Mining Company appealed to the board, and gained title to a Mexican land grant whose vague boundary came close to the middle of the New Almaden mining area. The bogus company claimed ownership of the mine, and in a celebrated trial, won control of it. Castillero received an injunction ordering him to cease mining. Barron, Forbes, shut down the mine on October 31, 1858, having produced over 9,000 tons of quicksilver since 1850.

In January 1861, Castillero appealed to the U.S. Supreme Court, and Barron, Forbes began mining again—flouting the injunction. The Supreme Court again voided Castillero’s title, but Barron, Forbes ignored the ruling and kept on mining. On May 8, 1863, in the midst of the Civil War, President Lincoln ordered U.S. Marshal Charles W. Rand to remove Barron, Forbes and Co. by force if necessary.

Rand, Lincoln's emissary Leonard Swett, and Quicksilver Mining Company President Samuel F. Butterworth showed up at New Almaden to enforce Lincoln’s order, but were turned back by 170 armed miners. Weeks later, a detachment of federal cavalry received orders to march from Sacramento to seize the mine. By this time, however, newspaper editorials had inflamed public opinion, suggesting that the federal government was planning to seize all of California and Nevada’s mines. Outraged, mine owners and workers began clamoring for California to secede from the Union.

Influential citizens, including Governor Leland Stanford and Nevada Territory Governor James W. Nye, sent telegrams to Lincoln urging him to rescind his order. Lincoln did, defusing the standoff. The dispute was submitted to international arbitration. Under a settlement approved by King William I of Prussia (Germany) on September 1, 1863, Butterworth’s company gained title to the mine by paying Barron, Forbes a sum equal to about three years of the mine’s production.

Over the years, the richest ores were mined out. By the 1890s, New Almaden ores contained only about 3% as much mercury as ores mined in the early 1850s. By 1900, its mine shafts went down as far as 2,450 feet—about 600 feet below sea level, deeper than any other quicksilver mine in the world. Little valuable ore was found. The Quicksilver Mining Co. gradually laid off its employees, and in 1912 went bankrupt.

When mercury prices rose during World War I, a new owner reopened the Senator Mine on the west end of the New Almaden property, and kept it operating until 1926. From 1928 until 1935 small amounts of mercury were produced by digging out old piles of spent ore and mercury-contaminated soil beneath furnaces, and heating them in the furnaces—in effect, New Almaden’s first environmental cleanup. In 1940, with war in Europe again pushing mercury prices higher, another company leased the property and again extracted mercury from the spent ore piles, and made open cuts in the hillsides to expose low-grade ore. One of the old underground shafts was also opened, and by 1945 these operations had produced over 250 tons of mercury.

When the war was over, New Almaden again shut down, though it continued to operate sporadically under a succession of new owners and leaseholders. The miners’ town on Mine Hill became a Civilian Conservation Corps (CCC) camp in the 1930s, but after World War II it fell into disrepair; many of the buildings burned down. Santa Clara County paid $4 million to buy more than six square miles of the hilly mine lands for a park in 1973 and 1975. By this time, oaks and madrones had reforested much of the property.

By the late 1970s, Almaden Quicksilver County Park looked, for the most part, natural, but the soil in some areas was still contaminated with mercury. These areas were fenced off and park plans put on hold while the county government leaned on the last three mining operators to pay for the soil cleanup. Under a legal settlement in October 1996, two companies paid a total of $2.5 million, with the county adding about $1.2 million more to finish the work.

A decade later, the cleanup was completed. High on Mines Hill, in the middle of the park, stood a rusty furnace the size of a house, used in the 1950s. Nearby, several acres of newly-contoured grassland had replaced the jagged scar of an open-pit mine excavated during World War II. The contouring prevents mercury-bearing rock from contaminating runoff that drains into Almaden Reservoir. Fishing is prohibited at Almaden Reservoir, because the fish are still contaminated. Near the park's Hacienda Trailhead on Almaden Road is a big, flat empty meadow—the only flat place anywhere in this hilly vicinity. This was where the reduction works, an imposing complex of buildings housing the furnaces, once stood. It was demolished long ago, but the ground is still contaminated, so the County Parks Department covered it with three feet of impermeable clay soil to prevent runoff from carrying mercury into nearby Alamitos Creek.

On Mines Hill, daffodils still bloom from bulbs planted by miners’ families in front of homes that have long since vanished. On weekends, mountain bikers fly down dirt roads that once bore wagons loaded with ore. For the history-minded, there’s a museum in the mine superintendent's old brick mansion on Almaden Road.

The Guadalupe and Silver Creek Mercury Mines: New Almaden’s Neighbors

The Guadalupe Mercury mine, adjacent to Guadalupe Creek in a steep valley about 10 miles southwest of downtown San Jose, was listed by the California Division of Mines in 1951 as having been the sixth most productive in the state. Its total production of over 3,800 tons of mercury, however, was dwarfed by its more famous neighbor, New Almaden.

The Guadalupe Mine started up in 1857. In 1861 surveyor William H. Brewer, writing in his journal (published as Up and Down California in 1860-1864) described it as "mostly in a valley between 'Mine Ridge' [New Almaden’s Mines Hill] and the main chain [the summit ridge of the Santa Cruz Mountains], and its workings [tunnels] extend down about 450 feet below the bottom of the valley." In the mid-1900s, mercury-bearing ore was excavated from an open pit near the old mine tunnel entrance. Mining ended in 1971.

Reduction works at the Guadalupe Mercury Mind, about four miles northwest of the Almaden Mines. Note large pile of firewood, burned to heat the ore and vaporize the mercury. Nearby oak forests were cut to provide this fuel.

Photo: Alice Iola Hare, c. 1900.

Upstream from the mine is 80-acre Guadalupe Reservoir; a trash landfill is adjacent to the mine site. The reservoir’s fish are contaminated by mercury, most likely from New Almaden’s runoff. Fish consumption advisories have been posted at the reservoir and along 18 miles of the Guadalupe Creek and River, all the way to its confluence with San Francisco Bay.

A 1997 inspection by the San Francisco Bay Regional Water Quality Control Board found another source of mercury pollution to the creek: The landfill operator had routed storm runoff through an open pit mercury mine. The water had formed a pond, which overflowed into the creek. The pond water had 0.71 micrograms of mercury per liter, nearly 30 times the Regional Board’s recommended limit. The agency ordered the landfill operator to reroute the runoff away from the mine pit.

The Silver Creek Mine was in the Silver Creek Valley, southeast of downtown San Jose. The creek’s name actually refers to quicksilver (mercury), not silver. The mine, operating by 1875, was known as the North Almaden mine in its early years. It has been inactive since the 1940s, and few traces remain. A 1997 inspection by the Regional Board found that one mine tunnel entrance was only 100 feet from Silver Creek, but water samples showed no significant mercury contamination.

Mount Diablo Mercury Mine Poisoned a Creek

The first mining claims on the east side of Mount Diablo were made in 1863. Originally called the Ryne Mine, the Mount Diablo Mercury Mine produced as much as 3.25 tons of mercury per month between 1875 and 1877. After that, the mine changed hands several times, closing when mercury prices dropped, and reopening when they rose.

The Bradley Mining Co. of San Francisco produced nearly 400 tons of mercury from the mine between 1937 and 1947. Between 1940 and 1952, the mine's production ranked ninth in the nation.

The Mount Diablo Mine had been an underground operation, with tunnels extending 165 feet below the surface. Starting in 1936, however , miners bulldozed an open cut into the side of the mountain to extract the ore, forming a 100-foot-high cliff. This exposed the ore to the weather, greatly increasing the contaminated runoff to nearby Dunn Creek.

Neighbors first filed complaints about water pollution from the mine in 1939. Continuing complaints resulted in a 1950 order for mine operators to stop polluting Dunn Creek because it flows into Marsh Creek, which flowed through a picnic area used by hundreds of people on summer weekends.

Jack and Carolyn Wessman bought the 109 acre-acre mine property in 1974, hoping to retire on the land. Aside from a few acres scarred by the mine, most of the land appeared untouched. The Wessmans’ retirement dream turned into a nightmare, however, when the last mine operator, the Guadalupe Mining Co. of San Jose, went bankrupt in 1977, leaving the Wessmans liable for the cost of stemming the flow of mercury into Dunn Creek.

In 1978, the state Department of Fish and Game (DFG) found that the highly acidic mine runoff was killing all life in Dunn Creek. In 1980, the DFG found mercury contamination in fish caught in Marsh Creek Reservoir, 10 miles downstream from the mine.

Jack Wessman spent his retirement bulldozing, capping, and recontouring piles of waste rock on his property, hoping to prevent contaminated runoff. In 2008, EPA identified another potentially responsible party, Sunoco Inc., and ordered the oil company to shore up a small dam that holds the runoff. Sunoco promptly did the work, but it was just a stopgap. In October 2014, the Central Valley Regional Water Board ordered Wessman, Sunoco and others to clean up the site by the end of 2016.(1)

St. John and Hastings Mines

The St. John Mine’s mercury deposit, in the hills northwest of Vallejo, was discovered in 1852. The mine operated in the 1850s, was closed in the 1860s, and reopened from 1873 to 1880, producing 438 tons of mercury by 1880. It was again reopened in 1899 by the St. John's Consolidated Quicksilver Mining Co., and operated sporadically until 1945. Total production amounted to 760 tons.

The nearby Hastings mine began operation in 1870, and continued sporadically until 1930, but it was never a major producer. In 1929 underground tunnelling exposed an acidic water source which flowed out of the mine, polluting nearby Sulphur Springs Creek. Local cattle ranchers successfully sought a court injunction to stop the pollution, and mine owners shut it down permanently.

A 1997 inspection of these mine sites by the Regional Water Board found an excavation scar with more than 10,000 cubic yards of tailings, high on a ridge. The agency’s report concluded that the sites were unlikely to cause significant contamination to waters in the area.

Napa County’s Mercury Mines

The most extensive cinnabar deposits in the U.S. were discovered in the 1850s and 1860s in the mountainous area around Mount St. Helena, where Napa, Lake and Sonoma Counties’ boundaries intersect. The area is dotted with mercury mines and hot springs, since volcanic activity here created mercury deposits and still heats ground water, creating geysers and hot springs. Several of the hot springs spas popular in the late 1800s are still operating in nearby Calistoga. Mines in this area were producing as early as 1864.

More than 50 mercury mines operated in Napa County alone between 1850 and 1950. The most productive were the Knoxville-Redington Mines and the Oat Hill Mine, opened in 1862 and 1876. Most of the county’s mercury was produced in the Berryessa Valley watershed, which today drains into Lake Berryessa. Napa County produced more than 13,500 tons of mercury by 1941, equal to 14.5% of California’s total, but very little after that.

Few visible traces of these mines remain, but their toxic legacy lingers: Fish consumption advisories posted around Lake Berryessa, one of Northern California’s premier recreation spots, warn people not to routinely eat bass or catfish from the lake, because they’re contaminated with mercury.

Two mercury mines at the far northern tip of Napa County, the Boston and the Manhattan, supported the mining town of Knoxville around 1900. A number of short-lived mines nearby had already been abandoned: the Reed, Andalusia, Royal, and Grizzly. Since the area was treeless, wood to fuel the mercury furnaces had to be hauled in by horse-drawn wagons from Lower Lake (in Lake County), a distance of 18 miles. The Manhattan Mine ultimately produced more than 2,500 tons of mercury.

In the 1980s, the Manhattan Mine site was swallowed up by the mile-long open pit of the McLaughlin gold mine (see Gold Mining, this chapter). No trace of the mercury mine remains.

Oakville’s mercury deposits, in the hills about two miles south of Rutherford in the Napa Valley, were discovered in 1860. Two major mines operated in the area: the La Joya, opened in 1865, and the Bella Oaks (aka Bella Union) in 1868. Both operated sporadically. The La Joya produced 77 tons of mercury before its final shutdown in 1931. An attempt to reopen it in 1943 failed due to tunnel cave-ins. The Bella Oaks, which closed in 1943, produced 68 tons.

A September, 1997 inspection of the Bella Oaks site by the San Francisco Bay Regional Water Board found a tailings pile, but no evidence of erosion that could pollute nearby creeks. At the La Joya site, the inspection found a partially eroded tailings pile that extending into a nearby creekbed. The report recommended erosion control measures to stabilize the tailings.

Notes:

1. California Regional Water Quality Control Board, Central Valley Region, Order R5-2014-0124, for Mount Diablo Mercury Mine, Contra Costa County, October 10, 2014.

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Excerpted from David D. Schmidt's San Francisco Bay Area: An Environmental History. Available from Backcountry Press.