The easiest of the burial mounds to locate is the one at SN75326 83939, marked as Cairn Circle on the OS Landranger map, just north of Hirnant Farm. Go through the gate just beyond the cattle grid, follow the fence along and go through another gate. The main cairn is in fact a circle of small stones. Like most of the Bronze Age mounds in this region, it had a low stone kerb to retain the earth. More on this at http://www.coflein.gov.uk/en/site/105582/details/HIRNANT+KERBED+CAIRN/ . Two smaller cairns just to the north-east at SN7536084047 and SN7539184002.
There is another kerbed cairn north-east of the dam, just off the Nant Maesnant-fach. A third cairn was excavated during the temporary lowering of water levels in 1984 and has now been reconstructed in a small fenced enclosure near the road. This one is a platform cairn, with a low stone platform rather than a mound inside the ring of stones. It may have been designed as a ritual ‘house of the dead’. These cairns are all described in Sian Rees’s book on the ancient monuments of Dyfed, though it is difficult to tie up her descriptions with the Ordnance Survey map.