Please see the listing for Sawbreaker #5 (GC3E9GK) for more information about the reservoir and dam as well as some neat pictures.
As for the cache- it is not at the posted coordinates! Do not go to posted coordinates unless you have a boat! Instead, go to waypoint "Dam Wall". Near here you should find a 4-digit number. Call this "x".
Next go to waypoint "Dam Shed". Near here you should find a 4-digit number. Call this "y".
If you found "x" engraved in a metal plaque, ADD it to the NORTH coordinates for this cache. If you found it engraved in stone, SUBTRACT it. If you found "y" engraved in a metal plaque, ADD it to the WEST coordinates for this cache. If you found it engraved in stone, SUBTRACT it.
Next SUBTRACT 100 from "y" and ADD it to the NORTH coordinates. Then SUBTRACT 10 from "x" and ADD it to the WEST coordinates. This should give you the location for the final cache.
And yes, you are looking for a bison tube hidden in the woods. ;-)
