Never heard of it in California. Granted, I probably have a "sheltered" group of friends and I have never smoked anything in my life. 
Yeah, I'm in Illinois and not familiar with the reference, but I've never really engaged in such an activity either. I'm still not sure that I understand what 420 or 4:20 has to do with smoking pot. I suppose it would make more sense if such activities were commonplace among my circle of friends? Seems odd.
It is from the late 60s or early 70s and started up in Marin County (you know where the rich people that work in san fran live (and where san quentin (sp?) is). It was "code" that a bunch of stoners would meet up and smoke at 420. so then it evolved.