1 2 McKinley, Jesse (April 19, 2009). "Marijuana Advocates Point to Signs of Change". The New York Times. Archived from the original on December 18, 2010. สืบค้นเมื่อ January 23, 2011. Mr. Hager said the significance of April 20 dates to a ritual begun in the early 1970s in which a group of Northern California teenagers smoked cannabis every day at 4:20 p.m. Word of the ritual spread and expanded to a yearly event in various places. Soon, cannabis aficionados were using "420" as a code for smoking and using it as a sign-off on flyers for concerts where the drug would be plentiful. In recent years, the April 20 events have become so widespread that several colleges have discouraged students from participating.
