The area is not officially defined but generally includes the group of falls on the Nedd Fechan, Pyrddin, Hepste and Mellte rivers, all of which lie between the villages of Pontneddfechan and Ystradfellte in the Brecon Beacons National Park.
The underlying geology is a generally southerly dipping succession of Carboniferous age sandstones and mudstones assigned by geologists to the Marros Group and formerly referred to as the Millstone Grit Series.
[3] Sgwd yr Eira – famous for being the falls behind which you can walk, the 'falls of snow' plunge over a hard band of sandstone whose overhang protects the walker from the full force of the water.
Stabilisation works agreed between the then landowners, the Forestry Commission and the Countryside Council for Wales and the Brecon Beacons National Park Authority allowed the route to be re-opened later in 2008.
There is a smaller visitor facility a few miles to the north operated by the National Park Authority at Cwm Porth near Ystradfellte.