4/20’s long, strange trip to mainstream acceptance.

As with so many things, we have the Grateful Dead to thank for 4/20.

Well — kind of. Maybe. Possibly. Probably? At least, in a roundabout way, which we’ll get to in a second. Parsing 4/20’s foggy history isn’t so simple, but the Dead do play a central role in the long, strange trip of the cannabis consumer’s sacred day into the mainstream.

Today, 4/20 isn’t much of a secret. Once simply a code of sorts for getting stoned, April 20 is now celebrated as a veritable holiday by appreciators of cannabis from coast to coast. Over the past decade or so, massive student smoke-outs at the University of California, Santa Cruz, and University of Colorado Boulder began receiving media attention. Now, with legalization spreading across the United States, even brands and marketers are getting in on the fun without shame.

But how did the holiday begin? Theories abound. You probably even heard one or two over a bowl while seated behind a hazy car dashboard back in high school or college. 420 is some sort of police jargon for marijuana, goes one. 420 is what you get when you multiply 12 by 35, says another — a play on the Bob Dylan song “Rainy Day Women #12 & 35,” which includes the frequently repeated line, “Everybody must get stoned.”

Other theories reference birthdays, death-dates and chemistry. Even if the roots are a bit murky, it’s kind of better that way, right? 4/20 just wouldn’t be 4/20 if it had an officially official history.

Storyteller makes no choice.

The stickiest origin story, the one that seems most credible, starts with a group of five California high school kids. It ropes in the Dead and then eventually leads to 4/20 as we know it today.

The kids were called the “Waldos,” because they used to hang out by a wall at San Rafael High School in Marin County, where they were students about 20 miles north of San Francisco. After school, according to the story they’ve told over the years, the five Waldos would meet up around 4:20, get stoned and hang out. If you’re picturing a scene out of Dazed and Confused, you’re not far off.

“We got tired of the Friday-night football scene with all of the jocks,” Dave Reddix, one of the original Waldos, told Time last year. “We were the guys sitting under the stands smoking a doobie, wondering what we were doing here.”

Eventually those three special digits became shorthand among the group of friends for, well, for you-know-what.

“I could say to one of my friends, I’d go, ‘420,’ and it was telepathic. He would know if I was saying, ‘Hey, do you wanna go smoke some?’ Or, ‘Do you have any?’ Or, ‘Are you stoned right now?’ It was kind of telepathic just from the way you said it,” Steve Capper, another Waldo, told HuffPost in 2011. “Our teachers didn’t know what we were talking about. Our parents didn’t know what we were talking about.”

Nowadays, of course, one’s teachers or parents would know exactly what you’re talking about. They might even ask to join. So how did 4/20 go from an inside joke among five friends to a universally recognized term for marijuana?

That’s apparently where the Dead come in.

In a word …

Jerry Garcia, Phil Lesh and company were already a world-famous rock-and-roll band by the early 1970s. After getting started in San Francisco’s Haight Ashbury district, the Dead decamped for bucolic Marin County, where they came to share some mutual connections with the Waldos. This network, the story goes, eventually made 420 a more widespread term for cannabis among the Dead’s extended circle.

It was at a Dead show in Oakland in 1990 that 4/20 apparently got its big break. There, Deadheads purportedly passed out a flyer promoting a plan to “meet at 4:20 on 4/20 for 420 in Marin County at the Bolinas Ridge sunset spot on Mt. Tamalpais” to get righteously baked. Mother Jones even got ahold of a copy of that fateful flier last year.

From there, if you believe the tale, 4/20’s journey to ubiquity had begun. But is this really the way 4/20 became cannabis shorthand and a quasi-holiday, with five high school kids and an assist from the Grateful Dead?

It’s impossible to say for certain—but it certainly makes for a good story to tell your friends over some holiday treats this April 20.