Their hair, once a symbol of youthful rebellion, is now shot through with grey. Bodies that writhed with wild abandon to psychedelic music sport stiff knees and wrinkles.
"How many of you are on acid right now?" rock critic Joel Selvin asked an audience of former hippies who turned out yesterday to mark the 40th anniversary of the Human Be-in, the counterculture event that set the stage for the Summer of Love. "How many of you are on antacid right now? "
In many ways, the '60s were born on 14 January, 1967 when musicians, poets, visionaries, student radicals and wayward youth gathered in Golden Gate Park.
Those who were there agree that neither they nor San Francisco have been the same since. Part rock concert, part protest, part literary festival, the Human Be-in was billed at the time as a "Gathering of the Tribes" meant to unite and stir up the various wings of the counterculture movement.
Estimates of the number of people who cavorted on the park's Polo Fields that day range from 10,000 to 50,000.
The speakers and bands who appeared reads like a "Who's Who" of 1960s icons: LSD advocate Timothy Leary, poets Allen Ginsberg and Gary Snyder, comedian Dick Gregory, the Grateful Dead, Jefferson Airplane.
Psychedelic drugs were in plentiful supply, courtesy of a parachutist who tossed free samples to the crowd. "Over the years, probably a dozen people have come up to me and said: 'You guys were fantastic!' laughed David Getz, the drummer for Big Brother and the Holding Company, Janis Joplin's band, which was not on the lineup that day. "I say: 'We weren't there,' And they say: 'No, I saw you!' Maybe they did."
By that summer, publicity about "the happening" , had encouraged thousands more young people to go to San Francisco with flowers in their hair.
At the commemorative forum, panelist Jim O'Donnell recalled the transformative days leading up to the Be-In. "My life turned from academia to sex, drugs and rock'n'roll - unfortunately, not necessarily in that order."
Like other panellists, O'Donnell and Getz remembered the Human Be-in as both the beginning and the end, an event that would be much duplicated but never equalled.
"The Human Be-in was a creation from within the San Francisco counterculture," Getz said. "The Summer of Love was a creation of the national news media that befell San Francisco."
Selvin noted that many of the young people who flocked to San Francisco that year were not emotionally equipped to handle the raw experiences they encountered and "some of them wound up as debris".
But Peder Jones, an educational publisher who attended the Be-in, said that despite the drug-soaked atmosphere, "not every hippie wound up incapable and penniless. We ended up doing jobs that didn't exist when we started college. The idea of groups doing things together started to make sense."