Every April 20th, weed smokers all over the country “observe” a sort of underground holiday of sorts, where marijuana is consumed on or around 4:20 pm  and depending on the circumstances, for an entire day.

As far back as pot smokers can remember, this “Weed Day” has been celebrated, but few can accurately recall its origins.

Some credit the seminal ’60s rock band The Grateful Dead. Supposedly some Dead fans coined the term “420-ing” when determining the best time and location to use the illegal drug.

“420 started somewhere in San Rafael, California in the late ’70s. It started as the police code for Marijuana Smoking in Progress. After local heads heard of the police call, they started using the expression 420 when referring to herb  Let’s Go 420, dude!” read a flyer distributed by Deadheads in the early ’90s.

However, High Times magazine did some research and found that 4/20’s roots go back to a more specific group of people  four San Rafael locals who dubbed themselves The Waldos back in the early 1970s.

The men all used the name Waldo at the time to protect their identities, but some of them have since gone public to share their story.

According to the Huffington Post, “One day in the fall of 1971  harvest time  the Waldos got word of a Coast Guard service member who could no longer tend his plot of marijuana plants near the Point Reyes Peninsula Coast Guard station. A treasure map in hand, the Waldos decided to pluck some of the free bud. The Waldos, who were all athletes, agreed to meet at the statue of Louis Pasteur outside the school at 4:20 p.m., after practice, to begin the hunt.”

“We would remind each other in the hallways we were supposed to meet up at 4:20. It originally started out 4:20-Louis, and we eventually dropped the Louis,” one of the original Waldos, Steve Capper, now 57, told Huffington Post.

Ironically, although the term 4/20 caught on, the Waldos’ attempt to procure the weed from the Coast Guard station were unsuccessful.

Still, this doesn’t solve the mystery of how 4/20 spread from being an inside joke between four friends to becoming a international phenomenon. Turns out The Grateful Dead were involved, after all.

One of The Waldos’ dads handled real estate business for the Dead, which gained the young men access to the band’s inner circle. They started using the 4/20 term frequently around the band, and it just became a part of the language of the era.

“We’d go with [Mark’s] dad, who was a hip dad from the ’60s,” said Capper. “There was a place called Winterland, and we’d always be backstage running around or on stage and, of course, we’re using those phrases. When somebody passes a joint or something, ‘Hey, 420.’ So it started spreading through that community.”

Now, High Times owns the 420.com URL and routinely pays homage to the “holiday.”

“I started incorporating it into everything we were doing,” Steve Hager, then editor of High Times, told Huffing Post in 2009. “I started doing all these big events  the World Hemp Expo Extravaganza and the Cannabis Cup  and we built everything around 420. The publicity that High Times gave it is what made it an international thing. Until then, it was relatively confined to the Grateful Dead subculture.”

Will you be celebrating this year?

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