Pen Allt-mawr

Pen Allt-mawr stands in the Black Mountains of south-eastern Wales as the third highest peak. Its summit rises 719 metres above sea level and overlooks the broad southern ridges of Waun Fach. The hill shares the skyline with nearby Pen Twyn Glas to the north and Pen Cerrig-calch to the south. A spur known as Pen Gloch-y-pibwr juts out one kilometre to the south-south-west. The stepped Bryniog ridge curves away from this spur toward the south. The summit area holds Bronze Age remains including damaged cairns and a large shelter cairn. A trig point marks the highest point on the stony ground. More Bronze Age cairns lie along the western edge of the plateau to the south. The geology shows a slab of upper Old Red Sandstone tilted toward the south. These Late Devonian rocks form a triangular summit surface shared with Pen Cerrig-calch. Beneath this layer are Early Devonian sandstones that shape the upper slopes of nearby hills. Visitors reach the summit across a plateau of weathered stone and Bronze Age ruins. The view stretches over the stepped ridges and deep valleys of the Black Mountains. The contrast between hard sandstone slabs and softer mudstone bands creates the stepped appearance of the hillsides. The Senni Formation sandstones appear on the lower slopes below the harder layers. Photographs from the area show Waun Fach and the surrounding peaks under clear skies.