What recent discoveries have been made about large underground voids under the United States?
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Executive summary
Recent reporting and industry materials show two linked threads about large underground voids in the United States: a surge of coverage about dangerous voids left by abandoned mines — with states like Pennsylvania hosting at least 5,000 such mine workings — and ongoing attention to engineered underground facilities and detection technologies for subsurface voids [1] [2] [3] [4]. Some commentators have amplified conspiracy claims about vast secret underground “cities,” but mainstream reporting documents known bunkers and continuity-of-government sites rather than the extraordinary $21 trillion network alleged by a former official [5] [3] [6].
1. Abandoned mines are the immediate, documented hazard
A string of December 2024 news stories reported sudden collapses and sinkholes tied to long-abandoned coal mines; authorities and geologists warn that mine subsidence has caused billions in damage and that areas such as Pennsylvania contain at least 5,000 abandoned underground mines that can collapse without warning [1] [2]. Experts describe typical collapse behavior — shallow, teardrop-shaped sinkholes from roof failure, voids filled with air, water or debris — and explain that some collapses are gradual and detectable by satellites while others happen rapidly and are hard to predict [1] [7].
2. Detection is getting more attention from industry and government clients
Industry solicitations and vendor materials show an increased demand for next-generation void-detection tools. A 2025 TechConnect initiative sought technologies to map significant subsurface voids at extraction sites in the U.S. and globally, noting both natural voids (erosion, dissolved bedrock) and poorly recorded artificial voids from prior mining operations [4]. Geophysics firms advertise ground-penetrating radar (GPR), seismic reflection and gravity methods to map void footprints and estimate volumes, indicating practical mitigation work underway in the private sector [8] [9].
3. Known underground government facilities are real — grand conspiracies are not substantiated by mainstream reporting
Mainstream reporting documents concrete examples of deep, secure facilities: Mount Weather and Cheyenne Mountain are part of a continuity-of-government network used to protect federal leaders in crises, and at least one FEMA-associated underground site has been publicly reported as receiving upgrades [3]. Separately, claims that the U.S. secretly spent $21 trillion building some 170 underground “cities” for the wealthy come from a former official and have circulated in outlets and opinion shows; those extraordinary claims are reported as allegations rather than corroborated fact in the sources provided [6] [5].
4. Two narratives can be conflated — public safety vs. secrecy narratives
Reporting about abandoned mine hazards and reporting about bunkers for government continuity occupy different factual terrains: the former documents physical, documented voids that endanger the public and property [1] [2]; the latter documents limited, long-known fortified facilities for government continuity, not a hidden national city network funded to the tune of trillions [3] [5]. The sources show that conflating routine remediation/detection work with unverified conspiracy claims risks confusing real, searchable risks with sensational allegations [4] [6].
5. What the sources specify — and what they do not
The sources specify the scale of abandoned-mine problems (at least 5,000 mines in Pennsylvania and widespread mine subsidence with billions in damage) and describe techniques used to detect voids (GPR, seismic, gravity) and industry programs seeking better tools [1] [2] [8] [4]. The sources do not provide independent verification of a nationwide $21 trillion underground “city” network; available sources report that claim as an allegation by a former official rather than as verified government spending or infrastructure documentation [6] [5].
6. Stakes and agendas to watch in the coverage
Reporting on abandoned mines is driven by public-safety and infrastructure concerns and by local officials and geologists emphasizing mitigation and monitoring [1] [7]. Industry solicitations for detection technology reflect commercial and safety interests of resource-extraction clients [4]. Claims of massive secret underground construction come from individuals and outlets that may have incentive to amplify scandal; mainstream outlets treat those claims as unproven allegations [6] [5] [3].
7. Bottom line for readers
If your concern is immediate public safety, the documented risk is collapsing, poorly mapped abandoned mine voids in multiple states and ongoing efforts to detect and map them using geophysics [1] [2] [8]. If your concern is secret nationwide underground “cities,” current mainstream reporting in these sources does not corroborate the extraordinary monetary and infrastructure claims; it instead documents known continuity-of-government bunkers and public debate about their upgrades [3] [6] [5].