On August 20, 1972, to mark the seventh anniversary of the 1965 Watts riots in Los Angeles—considered the city’s bloodiest unrest until the 1992 Rodney King riots—Stax Records presented a memorial concert for an audience of over 100,000 at the Los Angeles Memorial Coliseum. Featuring artists like Isaac Hayes, the Staples Singers, and Carla Thomas, Wattstax aimed to be an African-American response to 1968’s Woodstock—or “a day of black awareness,” as emcee Jesse Jackson says in his opening speech. Director Mel Stuart (Willy Wonka & the Chocolate Factory) combines footage from the music gathering, interviews with Watts residents, and snippets of effortless comedy by then-up-and-comer Richard Pryor for a joyous celebration of music that’s also an incisive reminder of one of L.A.’s greatest tragedies. Wattstax is a vital, powerful music doc not to be forgotten.