Most people think 420 was named after a police code, but that just isn’t true.

“We are going to meet at 4:20 on 4/20 for 420-ing in Marin County at the Bolinas Ridge sunset spot on Mt. Tamalpais,” reads the message, which Bloom dug up and forwarded to the Huffington Post. Bloom, then a reporter for High Times magazine and now the publisher of CelebStoner.com and co-author of Pot Culture, had never heard of “420-ing” before.

The flyer came complete with a 420 back story: “420 started somewhere in San Rafael, California in the late ‘70s. It started as the police code for Marijuana Smoking in Progress. After local heads heard of the police call, they started using the expression 420 when referring to herb – Let’s Go 420, dude!”

Bloom reported his find in the May 1991 issue of High Times, which the magazine found in its archives and provided to the Huffington Post. The story, though, was only partially right.”

Read the full story at The Huffington Post.