The data and the method

Two public United States Geological Survey files are read around any address, ZIP code or town, and every record in them is placed inside the Census Bureau town and county boundaries by its own coordinates. Each page then names the office in that state that holds the underground mine maps, because those maps, not these files, are the record that shows what runs under a parcel.

No page says that a mine is under a given house. A point in either file is a location, often the opening a surveyor saw at the surface, and the workings it leads to are drawn only on the mine map. Finding nothing in the files is not proof of nothing in the ground: a working that was never cataloged and never drawn on a survey sheet is in neither file, and on coal ground that describes a great deal of what was mined.

Every point of both files is tested against every county and every incorporated place by its own coordinates, with a ray casting point in polygon test and a one degree grid index, written without a geographic library. The county name written in the record is never used, because it is blank or wrong often enough to matter: all 12,958 Alaska rows of the mineral file carry no county name at all. A point that falls outside every boundary, offshore or in a gap, is counted in no county and no town.

Connecticut needed its own pass. The 2024 county file carries the state's nine planning regions, which no page is named after, so every Connecticut point fell in a region and the eight county pages read zero while 61 town pages carried records. The 2020 county file places them: 1,267 mineral records and 1,289 sheet features, seven of the mineral records falling outside every county, offshore.

Puerto Rico has no town or county pages on the site, so its 721 mineral records and 357 sheet features are placed inside the 78 municipios and named on the island's page rather than linked. The District of Columbia has no county, so its one town page is the District.

Both files record the same working more than once, and the mineral file does it to itself: the Halifax shaft at Tonopah is three records, a survey map shaft and two mineral file entries 25 meters apart. Records inside the same county are clustered when their names match once the filler words are stripped (mine, company, shaft, number, claim and the like), common abbreviations are expanded (Consolid. to Consolidated) and the town's own name is removed, and when they sit within 150 meters of each other. Two records whose names match exactly may sit up to 700 meters apart, because the mineral file itself says on the Roxbury Iron Mine record that it combined the record with the other Roxbury Iron Mine entry. A pair the file cross references that way is one site at any distance, and 164 pairs do. Records named for a mining district rather than a working are joined within 60 kilometers, since the file holds three rows called Tonopah District two kilometers apart.

What is never merged: an unnamed sheet feature, and a sheet feature whose name is only its own type, because a surveyor labels an unnamed hole with the word for what it is. That rule came from Litchfield, where 27 separate gravel pits had been folded into 11. The row that is kept takes the fullest written out name, the survey map position where there is one, the status of any record that has one (a producer's status code is zero, which an earlier test read as empty and threw away), the minerals of every record named once, and every record number, so nothing is lost and every merge can be undone by hand.

The result at county level today: 728,320 records became 681,415 sites, 46,905 of them folded into another. Inside town limits: 48,722 records became 45,424 sites. In the search tiles, 48,458 rows were merged so that one mine is one dot.

The mineral file holds 157 coal records in the country and the sheets only show a hole where a surveyor drew one, so Scranton showed five records while sitting on the anthracite. The coal fields layer closes that gap. Every town and county boundary is tested against the 993 polygons by its center and by up to 48 points of its own outline, because the layer is drawn at 1:5,000,000 and a town center can fall in a gap the small scale leaves. A place caught only at the edge of a field is told it lies on the edge, not over it.

1,148 counties and 4,964 towns sit over a mapped field. The 3,454 that sit over coal with not one record in either file carry a section of their own saying exactly that, because that is the purest form of the problem: a town over coal with nothing in the files.

The records are cut into 1,809 one degree tiles, the largest 1.45 MB, and the browser loads only the tiles the chosen radius touches. The point comes from a ZIP code centroid, a Census place, the Census geocoder for a street address, or the browser's own location, and the radius runs from half a mile to 25 miles. Filters by source, status, working type and mineral act on the rows after they load, so unticking every status box leaves no mineral file row, not all of them.

A tile that answers 404 is empty ground. Any other failure is said in words, not reported as nothing nearby, because on a page about safety an empty result after a failed load is a false all clear. Every run carries a token so a late answer from an earlier search is dropped, the search is written into the address bar so a link reopens the same result, and the tile addresses carry a version so a cached tile cannot answer with old data.

Where a place name is used twice in one state, Cottonwood in Arizona 171 miles apart for one, the search asks which. St. Louis, Saint Louis and St Louis all find the same place.

Download the two files and the two TIGER layers above, pick any county, place every point by its coordinates and apply the merge rules in the order given. The page prints the raw record count beside the site count so the merge can be checked on its own. Every row of the named list on a county or town page opens the USGS record it came from, or the USGS records at its own coordinates for a sheet feature that has no record page. To see what the surveyor drew, the USGS topoView shows every edition of the sheet, free.

Every external link on the 52 state pages was opened from this server when the pages were built, and where a host shields itself from a server the exact address was confirmed in a search index instead. The same was done for every link on these guides on October 29, 2026.

No guarantee

The mine information here is for general information only. Old mine records can be incomplete, outdated or wrong, and finding nothing here does not mean there is nothing there. Check with the mine map office named here before you rely on it, and have a qualified engineer look at any ground you are worried about. PublicRecordCenter.com assumes no responsibility or liability for any errors, omissions, or consequences arising from the use of this information.