Gary Duncan, guitarist and vocalist for Quicksilver Messenger Service, has died at the age of 72. Duncan’s Quicksilver bandmate and bassist David Freiberg confirmed the news to Rolling Stone, while Best Classic Bands cites a seizure and subsequent coma as the cause of death Saturday morning, according to sources close to Duncan.

Quicksilver Messenger Service were contemporaries of bands like the Grateful Dead and Jefferson Airplane in the rich psychedelic music scene of ’60s-era San Francisco and the surrounding Bay Area. The band’s founding lineup consisted of Duncan, Freiberg, guitarist John Cipollina, drummer Greg Elmore (Duncan’s bandmate in their former outfit, The Brogues) and multi-instrumentalist Jim Murray.

Duncan stuck with the band through their first two albums, their 1968 eponymous debut and 1969’s Happy Trails, before taking time away and eventually rejoining soon after until the band’s breakup in the late ’70s. Duncan and Freiberg revived Quicksilver as the main members of a new band under the same name starting in 2006.

“I’ve always thought of Gary as the engine of the original four-piece group,” Freiberg tells Rolling Stone. “He kind of taught me by osmosis, as I was a folkie 12-string guitar finger-picker, how to become a part of the machine. I felt he was always underrated as a guitarist. His solos with QMS were some of the finest ever. He was an amazingly talented musician—one of the best.”

Below, watch a video of Quicksilver Messenger Service from a spring 1970 concert at California’s Sonoma State College.