Just plucked this 420 commentary off the web:  

http://www.southcoasttoday.com/daily/04-03/04-20-03/a10lo043.htm

Can't vouch for anything it asserts.

Ron Roizen

-----Original Message-----
From: Alcohol and Drugs History Society [mailto:[log in to unmask]] On
Behalf Of Frederick Smith
Sent: Thursday, September 15, 2005 12:09 PM
To: [log in to unmask]
Subject: Re: 420

It's actually the date April 20 (4/20). I'm not sure why the date is
important though. Fred



--
Frederick H. Smith, Ph.D.
Assistant Professor
Department of Anthropology
Western Michigan University
Moore Hall
Kalamazoo, MI   49008
email: [log in to unmask]
office phone: 269-387-0408

----- Original Message -----
From: David Fahey <[log in to unmask]>
Date: Thursday, September 15, 2005 1:03 pm
Subject: 420

> My undergraduate students say 420 is marijuana slang, originating 
> in 
> California, that originally announced that a group would smoke a 
> joint at 
> 4:20.  Anybody with clearer information?
>