Vancouver is famed for its annual 4/20 protest, which is among the biggest in the world.

But as Geoff Turner, host of CBC original podcast On Drugs explains, the grandmother of Vancouver pot protests didn't even take place on 4/20.

A 1971 protest called the Grasstown Smoke In and Jamboree was one of the first major events to put marijuana legalization into the popular consciousness.

Marijuana was prohibited by the federal government in 1923, but became more widely embraced throughout the 1960s.

By 1971 there were 8,389 police reported incidents involving cannabis.

When the Vancouver Police Department started cracking down on users with raids and undercover officers, organizers called for an Aug. 7 rally in the Gastown neighbourhood — billing it the "Grasstown Smoke In and Jamboree."

When policemen on horseback charged suddenly into the crowd — reported to be several thousand — pandemonium ensued.

For more on the origins of pot protests in Vancouver, watch the video: