Modern-day folk rockers the Avett Brothers just wrapped an epic set at Mountain Jam. And during their 90-minute set, Grateful Dead legend Bob Weir strolled onstage to play some songs with them.

Weir joined the Avetts for takes on the Avetts' own 'Go to Sleep' as well as George Jones' early country classic 'The Race Is On,' a song the Dead used to cover in concert quite often back in the day.

Here's another video and a few pics from the show.