It's time for SXSW, the entertainment industry's annual mass pilgrimage to Austin, which means that for the next little while, music fans in Texas are going to be having all the fun -- and this year, that includes what Rolling Stone is calling "a massive free show" from Mumford & Sons, Edward Sharpe and the Magnetic Zeros, and Old Crow Medicine Show. Way to rub in in, Texas!

The free gig, held to celebrate the premiere screening of a documentary about the bands' 2011 railroad tour from San Francisco to New Orleans, will be held on the field at Austin High School. In keeping with the tour's theme of using outdated technology in new and exciting ways, the bands are partnering with MySpace to distribute tickets and offer a free webcast of the concert.

The documentary, titled 'Big Easy Express' and helmed by 'Under Great White Northern Lights' director Emmett Malloy, offers 67 minutes of footage from a one-of-a-kind tour that the band members still remember fondly. "The memories from that tour are tattooed on my mind," recalled Magnetic Zeroes multi-instrumentalist Nora Kirkpatrick. "When I first saw the finished film, it reminded me of what radiant moments live performances can create, and how powerful a group of minds can be when focused on the same goal."

"It’s not just the music," insisted Mumford and Sons’ Ben Lovett during a Rolling Stone interview held during the tour. "Everyone on that train has something that they put into the melting pot of this really complicated but beautifully balanced concoction. There’s no feeling of segregation between the musicians and the friends and everyone who’s doing everything else on the train. It doesn’t feel like three bands separately furthering their audience fanbases or any of that s---. It’s like, everything’s taking a backseat and everyone on that train has mucked in to make it what it is."

Watch the 'Big Easy Express' Trailer