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Bare feet, banjos and beer were as common as grass and eucalyptus trees in Golden Gate Park this past weekend.

Hardly Strictly Bluegrass, a free concert celebrating rock and roll, came through town with a wagon full of musical pioneers. People from across the country flocked for a cause not often honored: bluegrass, a joyous American relic like hoedowns and whiskey, both of which were back in style.

“I don’t even listen to bluegrass, but I appreciate that it’s there,” said Jason Steeley, who drove from Arizona with his wife and father-in-law. “It’s like apple pie, or the fourth of July.”

As the name implies, it’s a lot more than the southern sound, though remnants of the genre were present in almost all the acts.

This year the massive concert hosted idols like Led Zeppelin vocalist Robert Plant, festival staples like Emmylou Harris, indie godfathers Bright Eyes and other standouts like Buckethead and Broken Social Scene, who announced later that night they’re calling it quits.

Warren Hellman, a highly successful investor, music fan and San Franciscan, solely funds the concert each year, which started 11 years ago with the name Strictly Bluegrass, one stage, and 5,000 attendees. It has now expanded to six stages and estimates of 100,000 people a day, more than Coachella or Outside Lands attracts. Hellman is rumored to be a billionaire, and has hinted that he drops about $300,000 on the weekend, though that number rises every year.

He frequently describes the concert, which he has arranged to continue for 15 years after his death, as the “world’s most selfish gift.” The philanthropist, who plays in a bluegrass band called The Wronglers, even holds a special concert for local school kids on the Thursday before the event, where MC Hammer played to 44 school buses and 25 charter buses full of kids.