Green’s Dictionary of Slang

(drugs) marijuana; thus yerba buena/mala, good/bad marijuana.

1967		P. Thomas Down These Mean Streets (1970) 110: Nay, dad, I’ve been blasting yerba. I have a going high and I don’t want to mess it up.
1972		B. Rodgers Queens’ Vernacular 210: marijuana [...] yerba buena (Mex = good grass).
1997		Da Bomb Summer Supplement 8: Hierba buena (n.) Spanish for good herb; also, yerba buena. It is used to refer to marijuana.
2001		ONDCP Street Terms 23: Yerba mala (Spanish) — PCP and marijuana [...] Yerba (Spanish) — Marijuana.
c.2003		F.M. Figueroa ‘What The Soneros Are Saying’ at Picadillo.com 🌐 Here are a few additional drug-related terms that you may find in song lyrics: yerba – (grass) marihuana.
2012		J. Díaz This Is How You Lose Her 91: I had my yerba, she had hers.
2019		D. Winslow Border [ebook] You could drink, you could smoke a little yerba, but you couldn’t do chiva because no one can trust a junkie and a junkie is useless in a fight.