At Amoeba Music, there’s a new section called “Bay Area Hip-Hop,” with nearly 20-year-old albums from Totally Insane, the Click and RBL Posse. Something is in the air with Bay Area hip-hop, and it’s got one foot planted in the past. Last month’s Mob Figaz reunion show was completely sold out at the Phoenix Theater, and this week, the unlikely reunion of Marin County’s 51.50 brings back that classic Bay sound with “Games People Play,” “Green and White” and “Illegally Insane.” Mixing chill electro-funk with casual, reality-based rhymes, the group carved out a cult following worthy of their Twin Peaks samples before disbanding years ago. Relive the glory when they reunite on Friday, July 30, at 19 Broadway Niteclub. 19 Broadway, Fairfax. 9pm. $10. 415.459.1091.