April 20, or 4/20 in its calendar denotation, is a holiday celebrated by many weed-smokers both in the United States and around the globe.

It’s a day for smokers to celebrate their love of the intoxicating flower. Particularly in the U.S. where marijuana is not federally legal, it also serves as a rallying date for advocates of legalization.

Though there is no officially agreed upon story about the holiday’s origins, plenty of popular theories exist — perhaps the most famous tying the holiday’s date to a cohort of teenagers in California.

California is a state long known as a smoker’s paradise.

Popular lore ties the birth of ‘4/20’ to a group of high schoolers attending Northern California’s San Rafael High School in the early 1970s.

The cohort which dubbed itself the ‘Waldos’ used to gather at 4:20 pm to toke up.

‘We weren’t stupid stoners,’ Steve Capper, 68, an original Waldo said, pointing to a certificate for exceptional achievement and citizenship he received in school.

The point being, the Waldos engaged in after-school activities like sports and studying, so 4:20 was chosen as the time the group could all meet up.

The time stamp became code for the act of smoking weed, and eventually spread beyond the Golden State’s borders.

Dave Reddix, a member of the ‘Waldos,’ told TIME Magazine in 2017 that the band helped popularize the term during his tenure working as a roadie for bassist Phil Lesh.

TIME reports that during a December show in 1990 some Deadheads in Oakland distributed flyers inviting people to smoke ‘420’ at 4:20 p.m. on April 20.

Though other theories exist about the origins of 4/20, including references to a California police code and a Bob Dylan song, the Waldos have remained adamant that they are the true architects of the holiday.