We discovered this park a couple of years ago and thought it would be a great place for a cache. Seems jonboy had the same idea and you can visit his multi (visit link) while you are in the area. There's also a nature quest and literature describing the history of the old farm that used to be here. See kiosk near parking.
You're looking for a standard ammo can. It's near, but not in a rock wall, so no need to poke there.
There is a clue taped in the lid, and also found in the log book that will lead to the Go Fish (visit link) mystery cache.