Henry Diltz may not be the only person who can say he was at both West Point and Woodstock, but he’s the only one who has also taken pictures of Neil Young playing with nocturnal primates.

One Friday afternoon in August, after more than eight decades of wild and improbable life, Diltz was on the phone in his kitchen in North Hollywood, California, making arrangements to shoot some musician friends: the ’70s soft-rockers America, who were playing the following night.

Diltz was not the first of the great rock ’n’ roll photographers. Ask him, and he’ll name professional forebears like Jim Marshall, who also made defining images of the rock era — Hendrix letting a chord ring, Dylan kicking a tire, Johnny Cash flipping the bird.

But since Marshall died in 2010, Diltz, 85, who first picked up a camera 57 years ago, may be the earliest of the great rock photographers still living. He is certainly the oldest one still working.

Diltz falls asleep at night listening to George Noory on “Coast to Coast AM.” In the morning he does a series of chakra-awakening exercises and takes a few moments to say hello, in his head, to some of the people he has known who’ve gone to the other side.

He has survived many of his most famous subjects, some of whom he considered his best friends, like Dan Fogelberg, and David Cassidy, whom he met on the set of “The Partridge Family” and toured with for years. Diltz has survived Cass Elliot, a couple of Eagles, all but one of the Monkees. His wife, Elizabeth Joy Grand, died in 2001. A girlfriend of nearly 20 years passed away not long ago.

They’re the lucky ones, in Diltz’s view. The other day someone called and told him the news about Robbie Robertson. Good, Diltz said — he made it out. “The party’s on the other side,” he likes to say. It’s the rest of us, stuck over here, who have it rough.

Another old friend, David Crosby, died in January. He can be seen — alive and singing and goofing around, sometimes while dressed like a cowboy or Horatio Hornblower — on page after page of Diltz’s new book “CSN&Y: Love the One You’re With,” which collects the best of the countless pictures Diltz took of Crosby and his bandmates between the late ’60s and the present day. The book is a visual history of one band, a document of the ’60s and their long aftermath, and a record of Diltz’s own years of service at the front lines of the counterculture, which began in the early ’60s, at the military academy.

After a year, he got out and bought a banjo. By 1966 he was a touring folkie. One morning after a college gig in Lansing, Michigan, he and his band, the Modern Folk Quartet, tumbled out of their motor home and into a secondhand store.

Diltz’s bandmate Cyrus Faryar bought a cheap Japanese camera. To this day Diltz is not quite sure why he did the same. Sometimes he wonders how his life would have turned out if he’d gone to the kitchen department for a coffee mug instead.

Back home in Los Angeles, Diltz got his first rolls of film developed, and realized he had been shooting slides. He and the band invited all their LA friends over and loaded a carousel.

“That first slide hit the wall — it was our bass player, blowing up his cardboard bass case, in the desert, with M-80s,” Diltz said.

“That’s what hooked me,” he continued. “That’s when I became a photographer. That first slide hitting the wall, 8 feet wide, glowing in the dark — and my stoned hippie friends going, ‘Whoa.’ ”

Diltz would finally switch to digital cameras around 2005; before that, unless some band or label wanted a black-and-white photo for an 8-by-10, slides were all he shot. At his house the archive — about half of Diltz’s nondigital output — takes up one whole wall of the living room, latched plastic slide boxes stacked on wooden shelves, marked with printed labels or hand-lettered masking tape, and roughly alphabetized: “Elvis Costello” and “Phil Collins” are neighbors; “ELO,” “ELP” and “EWF” share the same box.

The archive is the product of nearly six decades of hanging out: at concerts in the wings or the pit, at Laurel Canyon hippie-pad parties, in backstage green rooms, in recording studios.

He had met Stephen Stills in 1963. He met Crosby a year later and Nash a few years after that, when Cass Elliot of the Mamas and the Papas brought Nash’s band the Hollies to the Lovin’ Spoonful guitarist Zal Yanovsky’s apartment for blender margaritas.

They hit it off. The next day, at Nash’s request, Diltz shot a portrait of the Hollies: five blokes in mod coats. To Diltz’s surprise, the image became the cover of “For Certain Because…,” the fifth Hollies album. It was his first real album cover, not counting “Hums of the Lovin’ Spoonful,” a record-company paste-up job incorporating some of his concert photos.

Eventually he met Gary Burden, who had been a Marine and became an architect but had never considered art direction as a career until Elliot, one of his home-renovation clients, asked him to design a cover for her solo album. Burden needed a photographer; he saw Diltz in the park at a love-in, taking pictures of hippies.

Over the next six years, they did dozens more together. Every used-record bin in America is a little Henry Diltz exhibit. The Doors loitering pretentiously at the Morrison Hotel. A sweet-baby-faced James Taylor. Jackson Browne’s face on burlap. Richard Pryor in a loincloth. A pensive Richard Harris, for “The Yard Went on Forever,” which credits Diltz with “Photography and Good Karma.”

Diltz’s most aesthetic- defining cover might be Crosby, Stills & Nash’s self-titled debut. It’s the antithesis of Marshall’s defiant Cash, or Hendrix with his flaming guitar: some guys in boots and jeans, sitting on an old couch on the porch of an abandoned house on Palm Avenue, just off Santa Monica Boulevard.

Many of the images in the book have a proto-Instagram intimacy. One series: Nash and Crosby in the back of a limo on the way to Big Bear, bookending Joni Mitchell, Nash’s girlfriend at the time. The book reproduces the whole roll: Crosby fooling around with a little American flag. Click. Nash kissing Mitchell’s hand. Click. A split second of doubt, him looking for her reaction. Click. Mitchell smiles.

In 1969, Stills’ former Buffalo Springfield bandmate Neil Young joined the band. Young shifted the group’s dynamic with his arrival. Diltz captures the mischief in Young, immortalizes him as an agent of chaos, the kind of guy who might show up one day with a bush baby on his shoulder.

Young was there, then he wasn’t. Forever after, Crosby, Stills & Nash’s history would be intertwined with Young’s presence and absence.

Crosby, Stills, Nash & Young would dissolve in drugs and enmity by 1970. By then the neighborly Laurel Canyon scene had faded too. Rock’s narrative began to play out on bigger and bigger stages. Diltz never stopped photographing bands, but by the ’80s he was spending a lot of time on music-video sets, two or three videos a week sometimes, trying to get a good shot of Heart or Poison.

Everything grew more professional, the age of access slipping away. When Diltz shot the Doors at the Hollywood Bowl in 1968, he was the only professional photographer there who didn’t work for a newspaper. Nowadays, the photo pit is crowded. But at the America show the next night, Diltz would be there anyway, waiting for something to happen — even though, these days, most places only let you shoot during the first three songs.

“I hate that,” Diltz said. “You have to walk away, and you miss all the great stuff that comes.”