The St John's Mine is a mineral extraction site approximately three miles north of the city of Vallejo

Vallejo, California

Vallejo is the largest city in Solano County, California, United States. The population was 115,942 at the 2010 census. It is located in the San Francisco Bay Area on the northeastern shore of San Pablo Bay...

 in Solano County

Solano County, California

Solano County is a county located in Bay-Delta region of the U.S. state of California, about halfway between San Francisco and Sacramento and is one of the nine San Francisco Bay Area counties. The county's population was reported by the U.S. Census to be 413,344 in 2010...

, California

California

California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

, United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. The St John's site was used for extraction of cinnabar

Cinnabar

Cinnabar or cinnabarite , is the common ore of mercury.-Word origin:The name comes from κινναβαρι , a Greek word most likely applied by Theophrastus to several distinct substances...

 in the early 1900s. The St. John's Mine is classified as a medium priority mine from the standpoint of environmental oversight. The last inspection of the Hastings Mine occurred in 1997 and found only slight erosion of the considerable mine tailings

Tailings

Tailings, also called mine dumps, slimes, tails, leach residue, or slickens, are the materials left over after the process of separating the valuable fraction from the uneconomic fraction of an ore...

; however the tailings exceed 10000 cubic yards (7,645.5 m³) of material, or one of the largest cinnabar tailings in the State of California. Furthermore, the drainage from St. John's Mine flows to receiving waters of Rindler Creek

Rindler Creek

Rindler Creek is a stream that rises on Sulfur Springs Mountain in southwestern Solano County, California. A stream restoration project has been conducted to reverse the damage of cattle overgrazing. One goal of this project is to enhance habitat suitable for the endangered Northern Red-legged Frog...

 and thence to Lake Chabot

Lake Chabot

Lake Chabot is a man-made lake covering in Alameda County, California. Part of the lake lies within Oakland city limits, but most of it lies in unincorporated Castro Valley, just east of San Leandro. It was formed by the damming of San Leandro Creek....

. Miles of underground shafts were driven in the course of working the quicksilver

Mercury (element)

Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

 deposits in the area. In 1989, Earth Metrics reviewed old 1918 maps of workings of the Hastings

Hastings Mine

The Hastings Mine is a mineral extraction site approximately northeast of the city of Vallejo, Solano County, California. The Hastings site on Sulfur Springs Mountain was used for extraction of cinnabar until the year 1930. The Hastings Mine is classified as a medium priority mine from the...

and St. John's Mines and found that mine shafts were not driven into the site prior to the year 1918.

Environmental effects

Principal ongoing impact is from mercury contamination of spring water flowing beneath the site; moreover, historical analysis has shown that the volume of spring water itself has been greatly reduced from levels of a century ago. This reduction of spring flow has come about due to the extensive mine shafts driven to achieve the cinnabar extraction.