Beneath the pit, some 370 miles of tunnels twist through solid rock, extending more than 1.5 miles below the surface. For 126 years, this site in Lead, S.D., housed the Homestake Mine, the deepest and most productive gold mine on the continent. In 2006, the Barrick Gold Corporation donated the mine to the state of South Dakota, which converted it into the largest subterranean laboratory in the United States, the Sanford Underground Research Facility. Although the lowest tunnels flooded after mining ceased, it is still possible to descend nearly a mile beneath the planet’s surface. Most of the sci­entists who do so are physicists conducting highly sensitive experi­ments that must be shielded from interfering cosmic rays.

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Persons: sci­entists Organizations: Barrick Gold Corporation, Sanford Underground Research, Sanford Locations: North America, South Dakota, United States