Saturday marks marijuana culture’s high holiday, 4/20, when college students gather — at 4:20 p.m. — in clouds of smoke on campus quads and pot shops in legal-weed states thank their customers with discounts.

This year’s edition provides an occasion for activists to reflect on how far their movement has come, with recreational pot now allowed in nearly half the states and the nation’s capital. Many states have instituted “social equity” measures to help communities of color, harmed the most by the drug war, reap financial benefits from legalization. And the White House has shown an openness to marijuana reform.

(T)he prevailing explanation is that it started in the 1970s with a group of bell-bottomed buddies from San Rafael High School, in California’s Marin County north of San Francisco, 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 nearby 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.