in the 1970s when a group of teenagers from San Rafael High School in Marian County would ritualistically smoke marijuana at 4:20 each day. The number 420 became their code for marijuana.
Subsequently, the term 420 ultimately became synonymous with the drug and was promoted by bands like The Grateful Dead.
After a two-year hiatus, San Francisco prepared for thousands of people to return to Golden Gate Park's Hippie Hill, for the annual 420 marijuana gathering.