The subject is a white, gender non-binary individual who is a native Angeleno. They have been smoking weed since age 13. We celebrated 4/20 a couple of days before I interviewed them and so I asked them to describe the holiday to me. Stoner culture is folk culture because for so long it was illegal to smoke. So the group is tight knit. I do not think a lot of the culture has been documented by academics so I wanted to look into it.
“4/20 is a sorta a holiday, like you can define it as a holiday. It’s when all the stoners celebrate, basically you smoke ridiculous amounts of marijuana. Fucking inject that. The actual, the most, what people think is the most truthful reason why it is a thing is pretty much there was a group of high school kids, somewhere in Northern California, where I do not remember, who pretty much their slang term for weed was four twenty because everyday after school they would meet up at 4:20 to smoke. And pretty much when the um, Grateful Dead were travelling around, they had the whole Deadheads following them too and pretty much at one point these deadheads met these kids, they use that slang and the slang simply got spread. And now it is THE number of weed. It was pretty much localized slang.”
Here is an article which lists several other folk beliefs on the origin of 4/20 and asserts this verison as true: http://www.laweekly.com/news/mythbusting-420-its-one-true-origin-and-a-whole-lot-of-false-ones-4177495