Is it socially acceptable to live in the past?

Apparently so, if you’re San Francisco rocker Mark Nelson. He and his sludge-heavy rock trio Electric Shepherd have pooh-poohed the digital age in favor of time-traveling back to the Bay Area’s halcyon 1960s era, when psychedelic outfits like Hot Tuna, Jefferson Airplane and the Quicksilver Messenger Service held transcendent sway.

That’s the spirit they’ve infused into their eponymous debut, and seven-minute epics like “Chem Trails,” based on the conspiracy theory that some sky-crossing jet trails are actually government-sanctioned chemicals surreptitiously sprayed on an unsuspecting public. (Hey — who knows? Alex Jones has made some valid points.)

The band just undertook an imposing-sounding “Awaken Sleeping Nations” tour (actually just nearly two dozen dates across America, so it would be “nation,” singular). But they’ve returned to wake up — then Blue Cheer-regress — San Francisco in Union Square tomorrow, from 6 to 8 p.m., as part of its Jewels in the Square concert series. Then, Nelson and crew will be taking part in the Frisco Freakout, Oct. 8, from 1:30 p.m. to 2 a.m., at Thee Parkside.

Stay retro-hip and up-to-date at www.myspace.com/electricshepherdmusic.