Very obscure one, this.... doesn’t feature upon any OS map I’ve seen and Coflein (currently) have no details either.... However CPAT (PRN 7820) have this to say:
‘Discovered during rapid upland survey in 1993. Roughly rectangular chamber with 3 orthostats on the NE seeming to form a constricted entrance. Capstones missing. Chamber surrounded by low stony bank probably the result of digging out the chamber from its covering mound and augmented by modern dumping. Most closely resembles a passage grave but other exemplars of that group are distant. The upland situation is unusual for chambered tombs in N Wales (Gibson, 2002, pp2-4).‘
So there you are. One of Wales’ great lost tombs, perhaps?