The Moat Boulder can be found at the far end of the boulderfield. You will notice a house-sized boulder perched in the middle of a marsh--that's it. The water level is dependent on the season, but the side facing the road usually offers the driest starts. It goes without saying (as I say it right now) that you should avoid this area during the spring, as billions of sadistic insects find their home at the base of the Moat Boulder.