There is a wealth of modern folklore about the origin of the term “420” and its connection to weed culture. But despite the myths, it isn’t a California police code, nor is it Bob Marley’s birthday (he was born in February) or the number of active chemicals in marijuana.

Of the many origin stories for the term 420 as code for all things herbal, the most credible traces back to 1971, to this statue of Louis Pasteur on the campus of San Rafael High.

The slang is said to come from a group of then-students who called themselves the “Waldos,” self-proclaimed for their usual hangout by a wall. One of them got hold of a map said to reveal a secret crop of weed, somewhere around a Coast Guard station at nearby Point Reyes. If only the toking Waldos could find that stash…

For weeks they hunted, meeting by the statue after practice (a couple of them were athletes) at 4:20 p.m. The secret code that the treasure hunt was on that day started out as “4:20 Louie,” but they soon shortened it, dropping the “Louie” and giving each other a simple “420” nod in the halls instead. It soon caught on throughout the school, and eventually spread to the local music scene, that at the time included some members of the Grateful Dead. Once they caught wind of it, the term spread like wildfire. Or, at least like smoke signals.

It’s been well over 40 years since those early days at the Louie statue, and 420 has become a universal symbol for pot smokers. It’s caused more than a few headaches for road crews too, including in Stratton, Colorado, where the 420 mile marker on I-70 was continuously being stolen.