In 1971, a group of stoners from San Rafael High School known as “Waldos,” named after the wall outside of school they could always be found perched against, coined the term. During the fall of that year, the Waldos got word of a mythical marijuana field that some Coast Guardsman was no longer able to attend to due to his service obligations. Seeing as the group smoked weed all day, every day, they were determined to find this crop and plunder it. But seeing as they were also high school athletes, their search would have to wait until after their respective practices. So what time did they decide to meet after school? That’s right: 4:20.
Since they searched day after day for the elusive field of green, they would excitedly remind each other during school “4:20.” The term stuck and eventually came to mean the same thing to that small band of pipe-dreamers that it does to the rest of the world today.
This doesn’t explain how it became a worldwide phrase, though. After all, they were far from the first, or last, group of teenagers to come up with an inside phrase. This is where the Grateful Dead comes in.
The band had recently moved out of San Francisco north to San Rafael after the Summer of Love had run its course and crime, drug addiction, and homelessness had replaced sex, drugs, and rock 'n' roll. This destitute existence was the oft-overlooked and -forgotten outcome of thousands of teenagers running away in search of a dreamlike existence that they never found. North of the Bay Area is where the band became acquainted with the Waldos, and more importantly 4:20.
One of the Waldos’ fathers managed property for the Dead and one of their brothers managed a band in which Dead bassist Phil Lesh played. So the Waldos were always around the band and, through a haze of smoke and other substances, the term eventually made its way through the band to the Dead Heads that followed them around. High Times, which has a close association with the Grateful Dead underground, eventually picked up the phrase and the term finally spread globally.