 The hill is formed largely from sandstones of the Brownstones Formation of the Old Red Sandstone laid down during the Devonian period.A part of the summit plateau is capped by sandstones of the overlying Plateau Beds Formation which also occur on the nearby peak of Fan Fraith.The Cribarth Disturbance, a north-east to south-west aligned zone of faulting and folding, passes through the hill.