This stone is found by walking through a number of fields from Owenynagat. This is cattle country with high barb-wire fences and lots of beefy cattle so I would regard this walk as only for the brave.
According to Michael Herity's book on the area "The standing stone of red standstone is 1.85m high, 1.4m by 25cm at the base. This Coirthe Dearg, Red Pillar Stone, reputedly marks the grave of King Dathí (Nath I), nephew of Niall Noíngiallach, Niall of the Nine Hostages, who was killed by a flash of lightning on an expedition at the foot of Sliabh n-Ealpa".
Niall was of course the slave dealer that brought St. Patrick to the Irish shores (or some my memory of primary school history goes).