It turns out that Borglum, the man behind Mt Rushmore, also built an underground area behind the giant presidential heads to be a “Hall of Records” (entrance pictured above).
“Into this room the records of what our people aspired to and what they have accomplished should be collected and preserved, and on the walls of this room should be cut the literal records of the conception of our republic, its successful creation, the record of its westward movement to the Pacific, its presidents, how the memorial was built and, frankly. Why.”
- Gutzon Borglum.
It was never completed past the first 70 feet, but a recent effort by the historical society placed a small cache of records there. Rushmore is an interesting case where one man’s obsession (carving the mountain into presidential faces) later became a monument synonymous with national identity. I had no idea there was a “library” like function also associated with it.