Throughout history, governments have kept certain activities hidden from the public, and whether warranted or not, the people in charge felt that it was the right thing to do at the time. Often when matters become declassified, the public has a tendency to misconstrue what happened and thus conspiracy theories are born. While not everything was hidden for a nefarious reason, these glimpses into history might give you a different understanding of historical events that have taken place.
After the Nagasaki and Hiroshima bombings in World War II, the US government conducted tests on thermonuclear devices. Operation Ivy was the eighth in the series, and it involved planned explosions on Elugelab. This photo is the first of them (the hydrogen bomb).
Original Plan For Mount Rushmore
Gutzon Borglum envisioned the Mouth Rushmore National Memorial to be much different, and the photo shows you what it was supposed to look like. Overall, they ran out of money while constructing the piece, so they stopped at the heads.