I have only read about this stone in local history books. I know the sight is near Devil’s Quoit very very little is known about locally.
There is a ref to the site at users.globalnet.co.uk/~tomgreen/folkgazt.htm
The stone is now lost but local legend says that this stone was once close the the Devil’s Quoit on the edge of Goss moor. The large stone was said to be deeply imprinted with the four horseshoes but the stone was overturned by tresure seekers.
The stone hasn’t been seen in living memory.
There is local legend that King Arthur lived at Castle-an-Dinas and nearby Goss moor was known as King Arthurs hunting ground.