The Brendon Hills are largely formed from the Morte Slates, a thick faulted and folded sequence of Devonian age sedimentary rocks. An east-west aligned anticline/syncline pair known as the Brendon Anticline and Brendon Syncline folds these rocks. The fold couplet is itself offset by displacement of the rocks on the NNW-SSE aligned Timberscombe Fault System. Over the centuries they have been mined for minerals, notably ironstone from which iron is extracted for making steel.