Big Bad Wolf has been holding this "Finding Area 51" contest where clues are given for us to guess where the book sale will be held and preview passes will be given out to 30 lucky winners. The latest clue, which is the picture below, is a dead giveaway.
There are still two clues left to be revealed today and tomorrow. I'm guessing there are clues for a more precise location, such as which building will the sale be.