You must have an ogre named Beatface (available via the Sparring Arena) in order to break Odd Boulder. After the ogre gladiator breaks the boulder, a chest will appear called Ancient Titan Chest that contains a smallish (I looted a stack of 18) amount of . Garrison Resources
However, it is possible to loot the chest even if you chose Lumber Mill instead of Sparring Arena. All you need is another player who chose to build the arena, and have them break the boulder for you.
For coordinates of all the boulders, see Odd Boulder's article on Wowpedia.