Carn y Defaid (N) is located in heather moorland just below the summit of Mynydd y Garn-fawr and to the north-east of a large summit cairn (NPRN 306237). It consists of a heap of loose rubble, mixed grade stones and small boulders, and measures 12m (east by west) by 11m with a height of 0.9m. On the east its height is nearer 1.5m where the cairn is perched on the edge of a steep slope down which part of its mass has spread. At its centre is a hollow 1.5m across and 1m deep. Despite this disturbance there is no clear evidence for structural detail.
The cairn's location here affords spectacular views across the lowlands of the Usk Valley.

David Leighton, RCAHMW, 25 November 2015