Historically, deep underground coal extraction in the United States involved complex multi-level shaft and slope operations, with various legacy historic sites—such as deep operations in Washington state's historic coal regions—recording extreme vertical depths exceeding thousands of feet below the surface and extending below sea level. However, modern U.S. coal production has shifted predominantly toward vast surface and mountaintop removal operations, particularly in the Powder River Basin of Wyoming and extensive regional surface mines across Appalachia, making ultra-deep subterranean coal extraction much less common in current commercial inventories.