How Did 4/20 Become Associated with Weed?

It's April 20th, also known as 4/20 - the day everyone associates with weed.  So how did the number "420" become connected to smoking reefer?

It's not because 4-20 is a police code for a marijuana bust, like you might've heard.  And it's not connected to Earth Day, which is two days later.

The consensus is it's just a slang term from a group of stoners that managed to catch on.

Apparently, back in 1971, some kids at San Rafael High School in California used to meet outside the school at 4:20 P.M. to hunt for a rumored hidden pot field -- smoking weed all the way.

Every day the group of kids would meet at 4:20 to hunt for the elusive marijuana field, so their code to meet was "4-20." They eventually started using "4-20" to describe everything related to marijuana - and the term spread when they used it around traveling Grateful Dead fans, who adopted it.

Eventually, "High Times" magazine heard about the "4-20" term through the Dead fans, and took it to an even wider audience.  And since April 20th is 4/20, it became the unofficial holiday for weed smokers.

[Huffington Post]