Wilco and Calexico came together at the Nelsonville Music Festival to perform "California Stars," a song by Woody Guthrie. This song was part of the album Mermaid Avenue, by Wilco and British singer Billy Bragg. The entire album was created from lyrics written by Guthrie after he had died, which were put to music by Wilco and Bragg. For this performance, Calexico provides some backing instrumentation comprised of accordions and trumpets to really fill out the song.
You can find Mermaid Avenue on iTunes.