Beth Harrington's lovely documentary The Winding Stream traces the history of the original Carter Family singers — Maybelle Carter, her cousin Sara, and Sara's husband A.P.— and their influence on American music. It doubles as a history of the spread of folk music, as A.P. "collected" regional songs such as "Worried Man Blues" to record, compositions whose original writers are unknown but which would have been lost entirely if not for the Carters recording them. Another briefly-touched on topic which needs its own documentary is their time on the 500-kilowatt border radio station XERA. The Winding Stream would duet well with theThe Wrecking Crewas celebrations of an obscure aspect of American music history,and like that film, the long production time results in the somewhat eerie new footage of long-deceased people like George Jones and Maybelle's son-in-law Johnny Cash. But most significant is the fact that as important as A.P.'s tireless song-collecting was, the real talents were Sara and Maybelle, the latter of whom invented a guitar technique called the Carter Scratch. The Winding Stream's one bum chord is the creepy cut-out animations used to represent the Carters singing in the 1920s. They briefly move the film from the holler to the Uncanny Valley, but even that can't stem the flow of the music.