Green’s Dictionary of Slang

gungeon n.

also gungun, gunion
[? ganja n.]

(drugs) potent marijuana, usu. from Mexico or Africa.

[UK]Marihuana Problem in City of N.Y. in Johnson Indian Hemp (1952) 35: ‘Gungeon’ is considered by the marihuana smokers as the highest grade of marihuana.
[US]P. Crump Burn, Killer, Burn! 258: ‘What’s pot?’ ‘Pot – weed – gunion – mexico joints. You know, weed, reefers.’.
[US]R.R. Lingeman Drugs from A to Z (1970).
[US]ONDCP Street Terms 11: Gungeon — Marijuana; Gungun — Marijuana.

In phrases

black gungeon (n.) (also black gunion, black gunny)

(drugs) an especially potent form of marijuana.

[US]R.R. Lingeman Drugs from A to Z (1970) 46: black gunion [...] extra potent, thick, dark, gummy marijuana.
[US]E. Folb Urban Black Argot 133: Black Gunny, a strong dark form of marijuana.
[US]E.E. Landy Underground Dict. (1972).
[US]J.L. Dillard Lex. Black Eng. 96: [Gunny] is ‘an old word which identifies a particularly strong form of marijuana found in Jamaica and Africa.’ Another form, Black Gungeon, is listed as related. Although the phonological relationship is not absolutely convincing, according to the Dict. of Jamaican English, this word may come from the same source as Jamaican ganga.
[US]E. Folb Runnin’ Down Some Lines 229: black gungeon Potent form of marijuana, usually gummy in consistency (grown in Jamaica and Africa).
[US]ONDCP Street Terms 3: Black gunion — Marijuana.