American hard rock's underground gets its own oral history here, tracing a line from 1970s proto-metal and psychedelia through desert rock and stoner sounds up to 2007. Director John Srebalus builds the film almost entirely out of interviews, putting musicians who rarely get profiled in front of the camera to talk through their own scenes: Mario Lalli and Eddie Glass from the Palm Desert generator-party circuit, Brant Bjork on Kyuss and what came after, Mark Arm on Seattle's grunge roots, Scott "Wino" Weinrich on doom, plus Lori S., Joey Osbourne, Scott Reeder, Billy Anderson, and John Gibbons among others. There is no host and no outside narrator forcing a single thesis; the musicians describe their own influences, gear, and small-label struggles, and the connections between generator parties in the Mojave, Sub Pop-era Seattle, and doom metal emerge from their accounts rather than from voiceover. The result plays like a genealogy of a sound nobody quite agreed to name, told by the people who made it.