Gary Duncan, a guitarist and singer for Quicksilver Messenger Service, an electrifying mainstay of the San Francisco psychedelic scene that rivaled Jefferson Airplane and the Grateful Dead in the late 1960s, died June 29 at a hospital in Woodland, Calif. He was 72.

His wife, Dara Love Duncan, said he had fallen 10 days earlier and suffered a seizure and cardiac arrest before being taken off life support.

Formed in California in 1965, Quicksilver Messenger Service helped create the “San Francisco sound,” fusing rock, blues, folk and jazz in a luminous blend that made them a staple of venues like the Fillmore, Avalon Ballroom and California Hall, where the air was filled with the smells of incense, marijuana and patchouli.

“You listen to these records and they take you back to a simpler time,” Rusty Goldman, a friend of Mr. Duncan’s and rock archivist known as Professor Poster, said in a phone interview. “Their music was pure. Everyone always left their shows feeling high on the music as well as whatever else they ingested.”

Mr. Duncan was not yet 20 when he joined Quicksilver Messenger Service and began making loose, heavily improvised music with drummer Greg Elmore, bassist David Freiberg and fellow guitarist John Cipollina, with whom he developed a complex, vibrato- and reverb-heavy interplay.

For a time, the band also featured guitarist Jim Murray and songwriter Chet Powers (known by his stage name Dino Valenti), a Greenwich Village folk singer who had written the peace anthem “Get Together” before being busted on drug charges that kept him from performing with Quicksilver Messenger Service in its early years.

Known for its brilliant, drug-infused live performances, the band initially resisted following peers like Jefferson Airplane into the recording studio. “We had no ambition toward making records,” Mr. Duncan once said, according to the website Best Classic Bands. “We just wanted to have fun, play music and make enough money to be able to afford to smoke pot.”

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But after 1967 performances at the Human Be-In and the Monterey Pop Festival, where they took the stage alongside acts including Jimi Hendrix, the Who and Jefferson Airplane, Quicksilver Messenger Service landed a contract with Capitol Records, resulting in their self-titled debut the next year.

Generally considered their finest studio effort, the record opened with a cover of Hamilton Camp’s “Pride of Man” — “Oh God, pride of man, broken in the dust again!” — and included “Gold and Silver,” a rock reworking of Dave Brubeck’s “Take Five,” co-written by Mr. Duncan.

Their follow-up, “Happy Trails” (1969), was described by Rolling Stone as “the definitive live recording of the late-Sixties ballroom experience,” and ranked No. 189 on the magazine’s list of the 500 greatest albums. Featuring extended jams built around the Bo Diddley songs “Who Do You Love?” and “Mona,” as well as Duncan compositions including “Cavalry,” it showed “that psychedelia was about more than just tripping out,” Rolling Stone wrote.

Offstage, band members lived at “a commune in Marin County where all manner of musicians, old ladies with babies, dope dealers and human driftwood coalesced into a barely functioning whole,” according to “A Perfect Haze,” a history of the Monterey Pop Festival by Harvey and Kenneth Kubernik.

“At rehearsals we’d sit there and play for seven, eight hours straight, 10 hours,” Mr. Duncan told ethnomusicologist Craig Morrison in 2001. “We’d play ’til we’d just fall over and the hands were bleeding. I’d go in the rehearsal place and take a bunch of amphetamine and some LSD and just play for like a day and a half. And end up in the weirdest . . . places, not knowing . . . if it was actually any good or not.”

After the release of “Happy Trails,” Mr. Duncan left the group for about a year — in part because of drug use, Freiberg said — and then returned to record “Just for Love” (1970). The album included Quicksilver Messenger Service’s only single to reach the Top 50, “Fresh Air,” as well as a fresh-from-prison Valenti, who took over lead vocals after Mr. Duncan and his bandmates had taken turns at the mic.

Mr. Duncan played on subsequent albums before the group disbanded after the release of “Solid Silver” (1975). He revived the Quicksilver name in the late 1980s and in recent years toured with Freiberg, who also performed with Jefferson Airplane and Jefferson Starship, groups whose popularity had long ago eclipsed that of Quicksilver Messenger Service.

“Nobody really wanted to be a celebrity,” Mr. Duncan once told the website Classic Bands . “That’s kind of like the way all of us are. Virgo is the sign of the hermit in the Tarot cards. We were all hermits and still are.”

By most accounts, Mr. Duncan was born Gary Grubb in San Diego on Sept. 4, 1946, and raised in Ceres, Calif.

He gave few details on his upbringing but said he was a Native American orphan who “grew up with rednecks,” built and fixed cars, worked at canneries, served in the military and spent a year in prison for marijuana possession before launching his music career in earnest. “I didn’t think I would live past 25,” he told Classic Bands.

Under the stage name Gary Cole, Mr. Duncan sang with the California garage-rock band the Brogues — their single “I Ain’t No Miracle Worker” was included on “Nuggets,” an influential compilation of early psychedelic rock — before linking up with Quicksilver Messenger Service.

They chose the name because four of the musicians shared the Virgo astrological sign, which is said to be “ruled,” in astrological terms, by the planet Mercury. Mr. Duncan recalled band members saying, “Well, let’s see — mercury’s the same as quicksilver, right? Mercury’s the messenger god? Quicksilver Messenger Service.”

In addition to working as a musician, Mr. Duncan had stints as a machinist, welder, diver, longshoreman and sailor, once taking a schooner from Malta across the Atlantic Ocean, through the Panama Canal, up to San Francisco and then across the Pacific, according to a 2007 report in Britain’s Observer newspaper.

He was also a self-avowed smuggler (of what, he did not say) and ran with the Hells Angels motorcycle group, declaring, “They can be dangerous and I’ve got a detached retina to prove it, but if they take you in, and they did, they’ll stay with you until the end.”

His marriage to Shelley L. Duncan — who wrote a memoir of their relationship, “My Husband the Rock Star” — ended in divorce, and in 1978 he married Dara Love. In addition to his wife, of Richmond, Calif., survivors include two children from his earlier marriage, Heather Duncan of Tracy, Calif., and Jesse Duncan of Merced, Calif.; three sons with Love Duncan, Thomas Duncan and Miles Duncan, both of Richmond, and Michael Duncan of San Francisco; and several grandchildren.

Mr. Duncan said he began playing the guitar because it was the instrument of rebels and tough guys. “If you’re going to play an electric guitar, you had to know how to kick people’s [butt], because they would be waiting to kick your [butt] when you came off the stage because they knew their girlfriends thought you was cute,” he told Morrison.

“Every guitar player I ever met was [nasty], because you had to be,” he added. “I had a guy walk up to me one time and punch me straight in the face when I was about 14 years old. I hit him in the back of the head with a Telecaster; he’s walking with a limp, now. I done him in. You had to fight to play.”

This story has been updated with additional information on Mr. Duncan’s death and surviving family.