The mountain is composed of Old Red Sandstone which dates back to the Devonian Era. The summit peaks are also composed of sandstone, but are much more resilient to erosion than the Old Red variety. As the glaciers in the area receded following the last ice age, the twin peaks of Pen y Fan and Corn Du were formed.

Pen y Fan, Wales, UK by Dave.Dunford

On the side of the mountain slopes along the path that leads from the Storey Arms to the summit of Pen y Fan, you will find an obelisk which was constructed and dedicated in memory of a five year old child who had died on the spot back in August of 1900. The child was the son of a coal miner from Rhondda who was on his way to visit his grandparents who lived near the Cwm Llwch Farmhouse. For twenty nine days the locals searched for the missing child before discovering his body where the memorial obelisk stands today.

Those who visit the mountains may also see military recruits along the paths leading to the top of Pen y Fan. Carrying a standard duffle, rifle plus food rations, those who want to join the UK Special Forces must pass the rigorous test that has become known over the years as the Fan Dance