April 20

The date, rendered 4/20, has evolved from the Waldos' 4:20 p.m. meeting time into an international cannabis holiday. The December 28, 1990 Oakland Deadhead flyer — which invited readers to "meet at 4:20 on 4/20" at Mount Tamalpais — was the first documented proposal to treat the date as an observance; Steven Bloom carried the flyer back to High Times (May 1991). The first organized annual event was the 4/20 Ball at Maritime Hall, San Francisco, on April 20, 1995. International gatherings include Hippie Hill in San Francisco's Golden Gate Park, the Denver Mile High 420 Festival, the University of Colorado Boulder Norlin Quad smokeout (peaking above 12,000 attendees before 2012 administrative closure), the Vancouver Art Gallery 4/20, and gatherings at Parliament Hill in Ottawa, Hyde Park in London, and Dam Square in Amsterdam. Post-2012 Colorado and Washington legalization transformed 4/20 into a major commercial retail event, with single-day legal sales exceeding $150 million across U.S. and Canadian markets on April 20, 2025.