Garreg Las

Garreg Las is a subsidiary summit of Fan Brycheiniog in the Brecon Beacons National Park in Carmarthenshire. Its broad north–south ridge, Esgair Hir, stretches across the moorland and reaches 635 metres above sea level. The hill is also known locally as Twyn Swnd. A kilometre north of the main top stands Carreg yr Ogof, a 585-metre subsidiary marked by a trig point. Its name means ‘rock of the cave’, reflecting the limestone geology beneath the grass. The geology of Garreg Las includes Twrch Sandstone from the Carboniferous period, with Carboniferous Limestone wrapped around its northern and western flanks. This limestone creates a karst landscape of shakeholes, one of which, Pwll Cynrig, holds water on the eastern slopes. The Twrch Fechan Fault runs along the eastern edge, bringing Old Red Sandstone into contact with the limestone. The karst features and exposed rock layers show how the landscape has changed over millions of years. On the summit lie two large prehistoric cairns called Carnau’r Garreg Las, each about twenty metres wide. A third cairn, Carn y Gigfran, stands a few hundred metres north of Carreg yr Ogof. These Bronze Age barrows are among many along the Brecon Beacons, likely used for multiple burials. A bridleway from Llanddeusant leads walkers up the northern slope, following part of the Beacons Way that crosses the ridge. The open moorland and wide views make the climb worthwhile for those exploring the range.