four-twenty, 420

There are many origin stories for 420, a slang term referring to marijuana, but unlike most slang terms, researchers have been able to pin down its actual origin with specificity. 420 was first used by a group of students at San Rafael High School in 1971, and it refers to the time of day, 4:20 pm, when they would meet to search for a mythical crop of marijuana plants.

San Rafael is in Marin County, on the other side of the Golden Gate Bridge from San Francisco, and in 1971 a group of students who called themselves the Waldos—because they used to congregate along a wall near the high school—got wind of a crop of pot plants allegedly growing near Point Reyes, further north. They would meet each day at 4:20 pm, after the school’s athletic practice, and venture north in search of the cannabis cache. They never found the pot, but in the course of their quest they smoked a lot of weed, had a lot of fun, and began using the term 420.

Marin County in the 1970s was also the stamping grounds of the Grateful Dead, and members of the Waldos had friends and family members associated with the band. 420 was picked up and used by Deadheads, as fans of the band call themselves, and from there the slang term spread to the wider world.

We have solid testimonial evidence that 420 was in use by the Waldos in 1971, but the first known use in print is from the Red & White, San Rafael High School’s newspaper from 7 June 1974:

If you had the opportunity to say anything in front of the graduating class, what would you say? [...] 4-20.

The OED archives also has a letter from Dave Reddix, one of the Waldos, from 23 September 1975, in which Reddix writes:

P.S. a little 420 enclosed for your weekend.

That’s the real origin. Among the false alternatives that have been proposed over the years are:

  • It was a police code referring to marijuana
  • It was a section of [insert state here]’s penal code referring to marijuana
  • It is the number of chemical compounds in marijuana
  • It was the date [insert name of famous rock musician here] died
  • It refers to Hitler’s birthday (Hitler was indeed born on 20 April, but the association with pot is never adequately explained).

There are many other explanations. All without any evidence.


Grim, Ryan. “Here’s the Real Story of Why We Celebrate 4/20.” Huffington Post, 20 April 2016.

Mikkelson, David. “The Origins of 420.”, 20 April 2017.

Oxford English Dictionary, third edition, March 2017, s. v. 420, n.

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