Geology
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 though the hill. The hill's finest feature is its north-eastern cwm which held a small glacier during the ice ages. The hill is within the Fforest Fawr Geopark designated in 2005 in recognition of the area's geological heritage.
Read more about this topic: Fan Gyhirych