On May 8, 1953, flying overhead at 19,000 feet, a B-50 bomber dropped a 27-kiloton nuclear device. Detonating at 2,323 feet, the bomb blew sections of the railroad trestle from its foundation and bent the girders. Additional structures in the area were constructed to measure the impact of other atmospheric tests. The Nevada National Security Site (NNSS), formerly called the Nevada Test Site, 65 miles north of Las Vegas, may be visited on a free tour offered once each month by Bechtel Nevada, the site’s contractor.
A 104 kiloton thermonuclear explosion on July 6, 1962 created the Sedan Crater in Area 10 of Yucca Flat at the Nevada Test Site. At 1,214 feet in diameter and 330 feet deep, Sedan is the largest nuclear-caused crater in the United States. The detonation was part of the Operation Plowshare program intended to find peaceful uses for nuclear detonations, such as excavations for harbors, canals, and open pit mines. The explosion created fallout that affected more US residents than any other nuclear test, exposing more than 13 million people to radiation. That was the end of Operation Plowshare.
The final planned underground test, named Gabbs, was planned for early 1993, but it was cancelled when the moratorium on testing came into effect in October 1992. The tower sits above the deep shaft into which the nuclear device would have been lowered. The hundreds of feet of data cables to connect the device to its monitoring equipment lie stretched out on the surface, ready to be lowered into the shaft in the event underground testing should resume. A virtual-reality view of the Gabbs tower may be seen here.
Nuclear testing at the Nevada Test Site began with a 1-kilotonne-of-TNT bomb dropped on Frenchman Flat on 27 January 1951. Many of the iconic images of the nuclear era come from the NTS.
During the 1950s, the mushroom clouds from atmospheric tests could be seen for almost 100 mi. The city of Las Vegas experienced noticeable seismic effects, and the distant mushroom clouds, which could be seen from the downtown hotels, became tourist attractions.
St. George, Utah, received the brunt of the fallout of above-ground nuclear testing in the Yucca Flats/Nevada Test Site. Winds routinely carried the fallout of these tests directly through St. George and southern Utah. Marked increases in cancers, such as leukemia, lymphoma, thyroid cancer, breast cancer, melanoma, bone cancer, brain tumors, and gastrointestinal tract cancers, were reported from the mid-1950s through 1980.