Carreg Dwfn (also referred to asCareg Dwfn andCarregydwfn and referred to also asCareg-y-dwfan[1]) is a hill four miles southeast ofLlandeilo and just to the south of the village ofTrap in the county ofCarmarthenshire, southWales. It lies at the western extremity of theBrecon Beacons National Park andFforest Fawr Geopark. Its summit at 283 metres (928 ft) is towards the eastern end of a rocky east-west-aligned ridge.[2]
The hill is formed from the coarseTwrch Sandstone (formerly known as the Basal Grit) laid down during theNamurianstage of theCarboniferous period. It is defined byfaults to east and west.[3] There are a handful of disusedgritstone quarries on the southern slope of the hill. Quarrying rights at these sites were stopped by theBrecon Beacons National Park Authority in 2008.[4] To its north is the large Craigyrodyn Quarry which worked theCarboniferous Limestone outcrop which parallels the narrow band of Twrch Sandstone running west to east through the region.[5]Glacial striae on rock surfaces high on the hill record that during the ice age, glacial ice travelled obliquely across it towards the southwest though lower down, to the south, the ice is recorded as moving more or less from east to west.[6]
Carreg Dwfn is designated as open country under the provisions of theCRoW Act 2000. Public footpaths run around the western, northern and eastern sides.
51°50′18″N3°57′11″W / 51.8382°N 3.9530°W /51.8382; -3.9530