Mountain Jam has only just gotten started, and already we have a signature collaboration featuring Warren Haynes with moe. Watch as they update "Opium," from moe.'s 2001 album Dither, during the festival's opening last night.

Haynes also sat in on Thursday with Railroad Earth, with whom he has recorded a new solo album. Planet of the Abts, featuring Haynes' longtime Gov't Mule bandmate Matt Abts performed at Mountain Jam, as well. Tonight's highlights at the Hunter Mountain, N.Y., fest include Robert Plant, Grace Potter and a special midnight performance by Gov't Mule of their recent Pink Floyd tribute Dark Side of the Mule. Black Keys follow on Saturday. Mountain Jam ends on Sunday, June 7; check out the fest's website for more information.

Can't make it this year? No problem: Mountain Jam is being streamed live through a partnership with Tourpedo, with all proceeds going to charity. Cost is on a pay-what-you want basis, with a $5 per-day minimum. Proceeds support Teen Cancer America, co-founded by the Who's Roger Daltrey and Pete Townshend. Fans can also track all the action with a brand new Mountain Jam app for mobile devices; it's available for both iPhone users and those using Android devices.

Haynes has regularly covered "Opium" with Govt' Mule, including a memorable performance at Mountain Jam in 2013. His new album Ashes and Dust is due on July 24.

See More Photos from Warren Haynes' Mountain Jam 2015 Appearance With Moe

Watch Bob Weir Perform with the Avett Brothers at Mountain Jam 2014