The centerpiece of “Jules Tavernier and the Elem Pomo” at the de Young is, as advertised, Tavernier’s recently rediscovered “masterwork” “Dance in a Subterranean Roundhouse at Clear Lake, California” (1878). Commissioned by Tiburcio Parrott, a wealthy San Francisco banking scion, the painting depicts a “mfom Xe,” or “people dance,” in an underground roundhouse (“xe-xwan”). For all its acumen and artistic prowess, contradictions tangle Tavernier’s “Dance.” On the one hand, the painting celebrates the intergenerational power of the Pomo as they pray for protection against decimation. On the other, though, the ceremony is performed in the presence of a small cadre of white men, including a banker (Tiburcio Parrott), his business partner (Edmond de Rothschild) and their peers, emissaries of the culture carrying out the decimation.