South Dakota’s Underground [google_map_easy id=”79″] Location: ? Jim River Valley South Dakota Functions: Unknown Levels: Unknown Tunnels to: Unknown Notes: “A Vast Underground Lake” discovered below the Jim River Valley which spans the borders of both states. Source: Location: Black Hills South Dakota Functions: Unknown Levels: Unknown Tunnels to: Unknown Notes: Plans for a large underground scientific laboratory within a large gold mine in the Black Hills. Source: Location: South Dakota Functions: Unknown Levels: Unknown Tunnels to: Unknown Notes: Source: