It was not till later we discovered a description of the origins of 4/20:
“The biggest celebration day in the cannabis culture is April 20. The April 20 (4/20) celebration originally started in the mid 1970s as the time of day after school, 4:20 pm, for high school students in San Rafael, California to meet to smoke pot. The phrase “I’ll see at you at 4:20” became code for, “I’ll be there to smoke a joint with you after classes are over”. Origins 4/20 Jodie Emery
While there we were so fascinated we went looking for more information: We asked a police man managing traffic if it was legal “NO”. How did it come to be allowed -“Because the Mayor is an idiot” was his frank reply.
Online found more at a Vancouver site.