This year marks the fortieth anniversary of the fabled Summer of Love, and the four- CD Love Is the Song We Sing: San Francisco Nuggets 1965—1970 (Rhino) commemorates the occasion with a thrilling showcase of the Bay Area sounds that defined a generation. These sounds weren’t just Californian, however. “Everybody get together,” coaxed Dino Valenti’s iconic song, and among those to gather in SF were an influential number of Texans: promoter Chet Helms, who founded the famed Avalon Ballroom and persuaded Janis Joplin to lend her talents to Big Brother and the Holding Company; psychedelic bluesman Steve Miller, who derided the early Grateful Dead and Jefferson Airplane for not being able to play; Miller’s onetime guitarist Boz Scaggs, who played Southern R&B until he heard disco’s call. Then there was that hottest of deejays, Sly Stewart, who was also a producer (of several key tracks here) before going on to lead his multiracial phenomenon Sly and the Family Stone. There are the usual licensing issues for such an endeavor (no Doug Sahm, and Joplin’s tracks are hardly representative), but this exhaustively researched set of the obvious and the obscure is still one hell of a trip.