The photo has been reprinted, posted and passed around for decades: Two grinning brothers, hair standing on end, unaware that they were minutes away from being struck by lightning while climbing Moro Rock in California’s Sequoia National Park.

“We were from San Diego and really stupid,” says Michael McQuilken, who was a long-haired 18-year-old when the snapshot was taken on Aug. 20, 1975. His brother Sean was 12.

“We thought it was something funny.”

But now, nearly 38 years later, McQuilken says he recalls that deadly afternoon in the Sierra Nevada mountains vividly: The flash of white light as bright as arc welding, the deafening explosion, the feeling of becoming weightless and being lifted off the ground.

Most of all, McQuilken says, he remembers the sheer power of a bolt from above.

“I never was cautious before that,” says McQuilken, now 56. “Now, if I’m out to climb a peak, I’m the first person to bail if clouds gather.”

The shocking experience attracted new interest this month when John Jensenius, the lightning safety specialist for the National Oceanic and Atmospheric Administration, discovered McQuilken’s blog post about the incident and shared it with a wide audience.

Jensenius, who keeps track of the nation’s lightning deaths for NOAA, says he’s been asked frequently about the photo, which was once used in brochures to help warn campers about the potential for danger. Contrary to rumors and some published reports, both brothers survived the strike, although another hiker was killed.

There were 19 deaths reported in August 1975, in a year that saw a final toll of 91, Jensenius says. Back then, however, lightning deaths weren’t well reported or tracked, he says, and the Moro Rock death wasn’t included.

Still, the photo serves as a gripping reminder of Jensenius’ ongoing mission to help keep people safe from lightning, which has killed an average of 53 people a year over the past 30 years. Fewer deaths have been reported in recent years — there were 28 in 2012 — largely because of better awareness and prevention efforts. So far this summer, 14 people have been killed by lightning. Every death means there’s room for improvement, Jensenius says.