Tenacious D will be stepping in for the Beastie Boys at this year's Outside Lands Music & Arts Festival, organizers announced Thursday.

The comic duo of Jack Black and Kyle Gass will headline the festival's final day, Aug. 30, with a set that Jack promised reporters during a conference call Thursday "may shake the foundations of the...San Andreas (Fault) and California may be shaken loose from the rest of the country. The question is, when that crack in the earth happens and it comes between your legs, where ya goin'? Are you goin' with America or are you going with Cali island. You have to make a split decision or you're going down in the lava."

Outside Lands is one of several dates the Beastie Boys had to cancel in the wake of the announcement of group member Adam "MCA" Yauch's battle with cancer. Jay-Z stepped in for the group at last weekend's All Points West festival in New York, and both he and Coldplay offered musical tributes to the Beasties.

Black noted that the Beastie Boys "are good friends of ours" after playing shows in 2008 to support then-presidential candidate Barack Obama's bid for the White House. "I think there's more similarities than difference, really when you put us together," Black said. "We had a good time playing on that bill." He also noted that Tenacious D has "been working hard on our hip-hop. Our next album is entirely rap and hip-hop with a sprinkle of maraca."

Black did tell Billboard.com that he and Gass are in the process of recording new material. "We just laid down a hot...we're calling it the bomb track. It's a very powerful recording called 'Deph Starr'...so it has nothing to do with the 'Star Wars' (Death Star). It's kind of sci-fi, doomsday rock." There's no word yet on when a new Tenacious D project will be released.

Outside Lands takes place Aug. 28-30 in San Francisco's Golden Gate Park and will also feature performances by Pearl Jam, the Dave Matthews Band, Black Eyed Peas, M.I.A., Modest Mouse, Incubus and Jazon Mraz.