The guy called in on his radio "4-20 in progress" maybe it was just something the cops of that area used based on the slang....
I honestly don't know. I was very much into smoking in high school - had many friends that grow etc. I live in Vermont, perhaps socially the most pot friendly place you can find in the U.S. I was pretty in tune with the smoking world for a young lad. My freshman year of college in 1994, my roomate was from California. Our first day in living together in the dorms it was 4:15 in the afternoon and he was like quick man, lets pack up that bong of yours its almost 4:20. I asked him what was so special about it and he said, I don't know, but if like to smoke, you should at 4:20. That was almost 11 years ago and I still don't know where it came from.
Is that so? "Nope. Section 420 of the California penal code refers to obstructing entry on public land. The penal codes of other states list different entries for 420, but none of them matches anything having to do with marijuana." From: http://www.snopes.com/language/stories/420.htm
here are some more ideas......................... -the 420/hemp connection - the score at the football game in Fast Times at Ridgement High, 42-0. - Bob Dylan's famous "Rainy Day Women #12 and 35" is a possible reference, or source -- 12x35=420 -Stephen Stills wrote (and Crosby Stills Nash & Young performed) a song "4+20" (first recorded 7/16/69, released on Deja Vu 3/11/70) about an 84-year-old poverty-stricken man who started and finished with nothing -Dylan aslo mentions "4 and 20 windows" in "The Balland of Frankie Lee and Judas Priest" -"The Waldos" were a group of teens back in the 70's that lived in San Rafael, CA. 420 was the way they talked about pot in front of teachers -Could be that it comes from hydroponics, the practice of cultivating plants in water often used by indoor marijuana cultivators, since 4 is used for H on a calculator (420/H20)