The origins of the date, and the term "420" generally, were long murky. Some claimed it referred to a police code for marijuana possession or that it arose from Bob Dylan's "Rainy Day Women No. 12 & 35," with its refrain of "Everybody must get stoned" — 420 being the product of 12 times 35.
But in recent years, a consensus has emerged around the most credible explanation: that it started with a group of bell-bottomed buddies from San Rafael High School in California, who called themselves "the Waldos." A friend's brother was afraid of getting busted for a patch of cannabis he was growing in the woods at Point Reyes, so he drew a map and gave the teens permission to harvest the crop, the story goes.
During fall 1971, at 4:20 p.m., just after classes and football practice, the group would meet up at the school's statue of chemist Louis Pasteur, smoke a joint and head out to search for the weed patch. They never did find it, but their private lexicon — "420 Louie," and later just "420" — would take on a life of its own.
The Waldos saved postmarked letters and other artifacts from the 1970s referencing "420," which they now keep in a bank vault, and when the Oxford English Dictionary added the term last month it cited some of those documents as the entry's earliest recorded uses .