SEATTLE (AP) — 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.

Here’s a look at 4/20’s history:

WHY 4/20?

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 derived 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 the 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. [Read More @ The Associated Press]