Trinity Site

Mushroom cloud from nuclear explosion
On July 16, 1945, the world's first atomic bomb was detonated approximately 60 miles north of White Sands National Monument.

White Sands Missile Range Photo


On July 16, 1945, one week after the establishment of White Sands Missile Range (WSMR), the world’s first atomic bomb was detonated in the north-central portion of the missile range, approximately 60 miles north of White Sands National Park.

For the Project Trinity test, the bomb was placed atop a 100-foot steel tower that was designated Zero. Ground Zero was at the foot of the tower. Equipment, instruments, and observation points were established at varying distances from Ground Zero. The wooden observation shelters were protected by concrete and earthen barricades, and the nearest observation point was 5.7 miles from Ground Zero.

At 5:30 a.m. on July 16, the nuclear device, known as “Gadget,” was successfully detonated. To most observers—watching through dark glasses—the brilliance of the light from the explosion overshadowed the shock wave and sound that arrived some seconds later. A multi-colored cloud surged 38,000 feet into the air within seven minutes. Where the tower had been was a crater one-half mile across and eight feet deep. Sand in the crater was fused by the intense heat into a glass-like solid, the color of green jade. This material was given the name trinitite. The explosion point was named Trinity Site.

Although no information on the test was released until after the atomic bomb had been used as a weapon, the flash of light and shock wave made a vivid impression over an area with a radius of at least 160 miles.

The world’s second atomic bomb, codenamed “Little Boy,” was exploded over Hiroshima, Japan, on August 6, 1945. Three days later, a third bomb codenamed “Fat Man,” devastated the city of Nagasaki. The Hiroshima bombing was the second artificial nuclear explosion in history, after the Trinity test, and the first uranium-based detonation. The bombs exploded at Trinity Site and Nagasaki had plutonium cores. A “Fat Man” bomb casing is on display in front of the WSMR visitor center.

After the explosion, Trinity Site was encircled with more than a mile of chain-link fencing, and signs were posted to warn people of radioactivity. The site was closed to both WSMR personnel and the general public. By 1953, much of the radioactivity had subsided, and the first Trinity Site open house was held in September of that year.

In 1965, Army officials erected a monument on Ground Zero. In 1975, the National Park Service designated Trinity Site as a National Historic Landmark. The landmark includes base camp, where the scientists and support group lived; the McDonald ranch house, where the plutonium core was assembled; as well as Ground Zero.

Today, visits to the site are sponsored by WSMR in April and October. The rest of the year the site is closed to the public because it lies within the impact zone for missiles fired into the northern part of WSMR.

Up to date information about Trinity Site open houses can be found at the White Sands Missile Range Trinity Site Open House page.

Last updated: December 6, 2023

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