Cairnfield of small cairns, presumably clearance cairns in the main.
Coflein/RCAHMW suggests it may be post Medieval, but Glamorgan Gwent Archaeological Trust have assigned a Bronze Age date. The site is certainly very similar to other Bronze Age cairn-fields in South Wales.
There is one possible funerary cairn at ST0276794150, described by GGAT as:
"Cairn in Carn y Wiwer cairnfield. Roughly circular with flat top, much better marked than other cairns in the group. Edges grass-covered, but the top has been denuded of vegetation (probably through placing of black plastic on top) revealing a mass of small pieces of sandstone (0.1m) set in dark earth. Dimensions: 5.7m diameter, c0.3m high."