I don't know the source of the following, my boyfriend sent it to me:
It is widely accepted that in 1971, a group of teenagers at San Rafael HighSchool in San Rafael, California, calling themselves "The Waldos", used tomeet every day after school at 4:20 p.m. to smoke marijuana at the LouisPasteur statue. The term became part of their group's salute, "420 Louis,"and it eventually caught on more widely. Many cannabis users continue toobserve 4:20 as a time to smoke communally. By extension April 20 ("4/20" inU.S. has evolved into a counterculture holiday, where people gather tocelebrate and consume cannabis.)There are also many apocryphal urban legends attempting to explain theorigin of the term. Two of the most common of these are that 420 refers tothe number of active ingredients in cannabis, or that it is police dispatchcode for cannabis. In actual fact there are around 315 active chemicals incannabis, varying depending on the exact plant used, and 420 has never beenverified as the police dispatch code for anything in any locale.