California Abandoned Mine Maps

Every office on this page was opened and checked on Oct. 22, 2026.

The 14,203 underground mine openings in California are spread across 58 counties, and the heaviest of them is San Bernardino County with 3,923. An opening on a historical sheet is a shaft, an adit or a tunnel that was drawn where the surveyor found it, so it marks a way into workings that run on underground, away from the point.

No guarantee

Everything here can be wrong. This is information, not a guarantee: the two federal files can be wrong, incomplete or out of date, the boundaries and the geocoder can be wrong, a point is a location and not a property line, and nothing on this page says that a mine is or is not under any particular property. Do not buy, sell, move, or make any decision about a home or about your safety on this alone. Ask the state mine map office named here for the maps, and have a qualified engineer look at the ground.

California publishes no mine map viewer of its own, so the federal archive is the route.

OSMRE National Mine Map Repository is the federal archive. It holds maps of more than 275,000 closed and abandoned mines, the images are not downloadable, and they are sent on request: search the repository by state, county, company or mine name, then ask for the sheet by its number through the map request form or at nmmr@osmre.gov.

A mine map is the only document that shows the rooms, the pillars and the depth of cover under a given piece of ground. A point in either federal file is a location, not a property line, and it says nothing about what lies under any particular house.

California runs no state mine subsidence insurance programme. Cover, where an insurer offers it at all, is an endorsement on a homeowner policy, and a standard policy excludes earth movement, which is what mine subsidence is.

Ask your own insurer in writing whether the policy covers subsidence from mining, and keep the answer. Seven states run a programme of their own: Pennsylvania, Ohio, West Virginia, Kentucky, Indiana, Illinois and Wyoming, with a protection programme in Colorado.

The topographic file holds 44,924 mapped mine features inside California, 14,203 of them underground openings. The sheets they were drawn on were surveyed between 1904 and 2004. The commonest kinds are prospect pit, adit and gravel pit.

The mineral file holds 31,580 worked or prospected sites in California, 30,782 of them named, with 14,076 sites recorded as a past producer. The commodities most often named are gold, sand and gravel and copper.

How the counting was done: every point in both files was placed inside the Census TIGER 2024 county and place boundaries by its own coordinates, not by the county name written in the file, because that name is blank or wrong often enough to matter. A point that falls outside every boundary is counted in no county and no town.

What the counts are not: a count of mines under houses. A single opening can lead to workings that run for miles, and a working with no opening on a sheet is in no count at all. Only a mine map shows the rooms, and only the offices named above hold the maps.

No guarantee

Everything here can be wrong. This is information, not a guarantee: the two federal files can be wrong, incomplete or out of date, the boundaries and the geocoder can be wrong, a point is a location and not a property line, and nothing on this page says that a mine is or is not under any particular property. Do not buy, sell, move, or make any decision about a home or about your safety on this alone. Ask the state mine map office named here for the maps, and have a qualified engineer look at the ground.