Trinity Site, where the first atomic bomb was tested at 5:29:45 a.m. Mountain War Time on July 16, 1945.
The 51,500 acre area was declared a National Historic Landmark in 1975. The landmark includes base camp, ground zero, and the McDonald ranch house where the plutonium core to the bomb was assembled. Visitors to a Trinity Site Open House see Ground Zero, “Jumbo” bomb casing, the McDonald House, one of the old instrumentation bunkers, historical photos, a Fatman bomb casing, and part of the original crater left by the explosion revealing “Trinitite”. (Greenish colored glassy substance formed by the heat and pressure of the explosion).