On Nov. 13, 1972, Terry Christensen was working in his office at Dixon Inc. on Orchard Mesa when he, like others, “felt the tremor.” He added. “We went out and saw the smoke. We saw a mushroom cloud, which was visible for a few minutes. Then we went back to work.”

It was interesting, but also anticipated, he explained. “We were expecting it.”

The mushroom cloud wasn’t from a nuclear bomb, but from the explosion of 500 tons of TNT, set off to mimic the effects of a small nuclear explosion.

Christensen and his colleagues weren’t alone. People in many offices and homes throughout the Grand Valley that morning witnessed smoke from the blast in an isolated spot on Glade Park. Windows rattled in the valley, and many people felt the ground tremble.

Later that day, an article in the afternoon

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