A recent visit to the site of the first atomic bomb explosion offered desert vistas, (mildly) radioactive pebbles and troubling reflections.

— Once, in another lifetime, I witnessed an atomic explosion.

This was in the 1960s at the Nevada Test Site, a vast area about an hour northwest of Las Vegas where the American military tested bombs.

I was working for EG&G, a military contracting company that, among other atomic chores, supplied all the instrumentation for the test site; it is now part of a company called Amentum.

The ground bulged, and a line of torches marking ground zero flew into the air.

Army opens the gate to the White Sands Missile Range in New Mexico, allowing in civilians to tour a patch of sand known as the Trinity Site, where the very first atomic explosion was set off and the history of nuclear dread began.

He had never visited the Trinity Site — he hadn’t known you could go there until recently, he said.

The bomb would use explosives to squeeze a softball-size lump of plutonium to critical density, ideally resulting in a soul-rattling explosion.

6, 1945, a bomb of slightly different design was dropped on Hiroshima, killing an estimated 140,000 people.

Fat Man, a plutonium bomb of the kind tested at Trinity, was used on Nagasaki on Aug.

At Trinity’s ground zero, hundreds of people were milling around as if at a county fair, but there was little to see.

The detonation created a crater eight feet deep, a half-mile wide and lined with glassy pebbles called trinitite: sand that had been swept up in the fireball, vaporized and then fell back down in molten radioactive droplets.

An obelisk of black rocks, with a plaque commemorating the event, marked the exact point of ground zero; we took turns posing in front of it and a life-size model of Fat Man, which resembled a short, bulbous submarine with enormous tail fins.

The ground below our feet was littered with green shards of trinitite.

The signs seemed to remind visitors to bend down and retie their shoelaces, perhaps to gather a promising souvenir or two of the original sin in the process.

I was hoping that my pebbles would be at least as radioactive as a banana, but my friend’s verdict came the next day.

Stanislav Petrov, a lieutenant colonel in the Soviet Air Defense Forces, was in charge that day of a command center called Oko (“eye,” in Russian), an early-warning system that relied on a network of satellites to detect attacks.

But Colonel Petrov, an engineer by training, held back, worried that the signal might be a false alarm.

Colonel Petrov erupts

Asked if atomic bombs would ever be used in war again, Colonel Petrov pauses