As we reported, Bruce Springsteen delivered the keynote speech at the SXSW conference in Austin, Texas yesterday (March 15) -- and as intellectually-edifying as that may have been, it was the jam session afterward that really got people talking.

After playing a few songs of their own, Bruce and the E Street Band were joined by scores of other musicians for what's been described as a "face-melting" cover of Woody Guthrie's 'This Land Is Your Land.'

So who was there? Members of Arcade Fire and the Low Anthem, Garland Jeffreys, Tom Morello from Rage Against the Machine, and Austin music legends Alejandro Escovedo and Joe Ely.

The song pick wasn't entirely a surprise -- Springsteen is a long-time fan of Guthrie's and even paid homage to the folk singer (who would've been 100 this year) in his keynote address, saying:

In Guthrie’s work, he found a way forward: ‘fatalism tempered by a practical idealism,’ and a conviction that ‘speaking truth to power wasn’t futile.'

The Boss may have considered the raucous jam session a celebration of sorts -- his new album 'Wrecking Ball' topped the charts in its debut week. And on March 26, he'll play a part in helping a sick little boy's fondest wish come true.

Watch Bruce Springsteen and Some Friends Jam on 'This Land Is Your Land'