Cwm Idwal comprises volcanic and sedimentary rock which was laid down in a shallow Ordovician sea, and later folded to give rise to the distinctive trough-shaped arrangement of strata known today as the Idwal Syncline.
The Cwm Idwal region consists of both volcanic and sedimentary rocks formed in an ancient shallow sea during the Ordovician period. These rocks were then folded, resulting in the characteristic trough-like shape seen today in the Idwal Syncline.