Some people need weed.

[Thumpalumpacus]

And how accessible and well-known was it? It was probably almost as obscure as salvia divinorum is today. 

Just like today, that depended on who and where you were. Marijuana use rates amongst blacks and latinos were high enough to garner Federal concerns, and indeed, one reason it was outlawed was because such outlawing was seen both as a demotivator to Mexican immigration and one more petty injury to be inflicted upon blacks in the days of Jim Crow.

This is a pretty interesting article about the topic, covering particularly the influence of Mexican-American labor relations: https://libcom.org/library/4-mexican-ame...-1930-1937