Trinity Atomic Test Site
"Trinity" was the codename of the first detonation of a nuclear weapon and was conducted by the United States Army in 1945 as part of the Manhattan Project. The only structures present at the time were the McDonald Ranch House and its ancillary buildings, which scientists used as a laboratory for testing bomb components. There were 425 people present in the base camp on the weekend of the test. The test site was declared a National Historic Landmark in 1965 and listed on the National Register of Historic Places the year following.