420=pot in LA Times

[Grant Barrett]

This article explores the connection between "420" and marijuana. Not half
bad original research. The writer, Shawn Hubler, claims to have nailed the
story down and elaborates on the origin that was reported here previously.
One of the men supposedly involved in the Seventies claims to have written
materials from back then using 420 in its current context.

http://www.latimes.com/news/local/la-000028188apr20.story?coll=la-headlines-
california-manual