Some believe it's the number of active chemicals in marijuana, others that it's based on teatime in Holland.
This one is a bit of a stretch, but some have attributed the origins of 420 to Bob Dylan's song "Rainy Day Women #12 & 35".
The pot search routine went on for weeks and the group agreed to meet every day at "420 Louis" to continue the search.
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. Lovers of pot extra-indulge in the burning of the sacred herb.
"We would remind each other in the hallways we were supposed to meet up at 4:20".
They never did score the free bud, but perhaps they stumbled on to something more lasting? So how did the number 420 come to represent smoking pot? It's a tale involving dairy pioneer Louis Pasteur, the Grateful Dead and five high school athletes.
Members of the Waldos had open access, and many connections, to the band.
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"We have no idea", Waldo Steve told Yahoo News. "When somebody passes a joint or something, 'Hey, 420.' So it started spreading through that community".
Waldo Steve's older brother, Patrick, managed a Dead sideband, Too Loose to Truck, and was friends with the Dead's bassist, Phil Lesh.
The first time Steven Bloom ever heard the phrase "420" was during Christmas week at a Grateful Dead concert in Oakland, California, in 1990 while he was a reporter for "High Times".
The Waldos not only spoke with an editor at High Times (not Bloom) and signed statements attesting the truth of their story, but they also provided documents, such as old letters referring to marijuana by its numerical nickname, old high-school newspapers using the term, and even a "420", batik-dyed marijuana flag, according to 420Waldos.com.
The real story apparently traces back to northern California. They encouraged (or pleaded with) their students to not participate-to no avail.
Today, there's a 420 rap music festival in Portland called Cloud City - the largest musical celebration in the Northwest. No one fessed up to being responsible for the fortuitous number, but was likely a staffer in California State Assembly Member Mark Leno's office.
So at 4:20 pm they embarked on a "treasure hunt" which would eventually fail but create a counterculture of sorts. Even the 1990s Nickelodeon cartoon "Rocko's Modern Life" featured a clock reading 4:20. They had come across a hand-drawn map of a marijuana crop somewhere at Point Reyes, north-west of San Francisco, and they wanted to get their hands on that.