Outside Lands organizers have been sitting on the full lineup and waiting to release it on June 1st, but yesterday some eagle-eyed music fans noticed that an ad a sidebar in the new issue of Spin has hit stands ahead of this release date showing the full a partial line-up, which includes headliners Kings of Leon, My Morning Jacket, and Phoenix, with The Gossip, soul legend Al Green, and BlackStar also on the bill.

This appears to have been an oops on the part of Another Planet and Spin, but hey, in the internet age, the fact that it's ever possible to keep these things under wraps is beyond us.

The festival is compressed back to two days this year, on August 14 and 15, in Golden Gate Park. Tickets go on sale at 10 a.m. on Tuesday, June 2. [Examiner]

Update: Our June issue of Spin, which came in the mail earlier this week, contains no such ad. But City Sound Inertia has a bunch of guesses of other acts, based on Ranger Dave's Twitter riddles, including Bassnectar, Chromeo, Devil Makes Three, Edward Sharpe and the Magnetic Zeroes, Social Distortion, Tokyo Police Club, and Temper Trap. Owl Mag features some legal downloads of some of the above. [Hat tip: East Bay Express]

Update: Yeah, so thanks to commenter fyodordos, we see the leak, which is on page 72 of the June issue of Spin, and it's just the partial lineup mentioned above. We're starting to wonder if this wasn't a planned tease, with a few more, bigger names to drop on Tuesday.