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The Cambrian Mountains lie between the mountains of Snowdonia in the north of Wales and the Brecon Beacons in the south, inland from the coastline of Ceredigion but west of the central Welsh farmlands.

They can be characterised as a dissected plateau broken only by glacial gouging and by the deep clefts of river valleys: these two processes together have created the landform which exists today.   In the south, the upland terrain gradually descends to join the Cothi valley, north of the foothills of the Black Mountains.

The Cambrian Mountains are made up of three distinct upland blocks, from north to south;

  • Pumlumon – a massif with five peaks, including the highest point Pumlumon Fawr, holding the sources of two major rivers, the Hafren (Severn), and Gwy (Wye) as well as the Rheidol;
  • The Elenydd – the central range, whose east side runs down into the English speaking areas of central Wales and the Wye Valley whilst the western side slopes off gently into the Welsh-speaking heartlands of Ceredigion.  It is the source of the Teifi in addition to several tributaries of the Gwy including the Elan; and
  • Mynydd Mallaen in the south – with the headwaters of the Tywi (the longest river flowing entirely in Wales). It is an exposed area of unenclosed grazed upland plateau, dominated by heathland and wetland plant communities with bilberry, heather and wet heath mosaic. The plateau drops down into the surrounding valleys through fridd habitats, grassland, rocky scree in places and woodland. The area is Common Land with open access. The plateau is marked by one or two cairns, otherwise it creates a very gentle almost level skyline. There are tracks across the area. There are no trees, nor field boundaries but several rocky outcrops and wet depressions. The area provides extensive views in all directions, and feels extremely exposed, wild, empty and isolated.
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The spectacular gorge and waterfall at Dylife was formed by the deep-cutting headward erosion of the Twymyn-Dyfi to capture the uppermost Clywedog-Severn valley. Similarly, the River Teifi was first diverted by rapid headward erosion of the River Ystwyth along the line of the Ystwyth fault, and then the Ystwyth headwaters in turn were captured by the River Rheidol. The shortened route this provided for the river to the sea from Devils Bridge (10 miles compared with the previous 50 miles to reach the coast at Cardigan) caused the Rheidol to deepen its bed very rapidly, creating the famous waterfall and gorge at Devil’s Bridge.