The falls occur on a geological fault on the river Nant Llech and have retreated up the valley by up to 165ft (50m) since the last Ice Age. The hard layer of sandstone forming the lip of the waterfall is known as Farewell Rock. Coal miners digging down to this layer in the mines of the South Wales valleys would say 'farewell' as there was little chance of finding coal below it.
In the mid-1800s the area was surveyed by William Logan, an internationally noted geologist. While surveying for a detailed geological map of the South Wales coalfields he found two fossilised trees at the base of the falls. You can now see them outside Swansea museum.
If you walk quietly along the footpath in the valley, you may see woodland birds like woodpeckers, tree creepers, warblers and wrens. Dippers and wagtails are often seen hunting for insects along the river. Trout have also been seen trying to jump the smaller lower falls.
The damp, heavily wooded gorge, with its thin soils and steep rocky slopes, is a haven for shade and damp-loving plants. Keep your eyes peeled for mosses, liverworts and lichen. Their presence is why the area is designated as a Site of Special Scientific Interest (SSSI).
There are two walks from the car park at Henrhyd (link to external site)
. If you want to just visit the waterfall, follow the path from the car park down the well-made path to the junction at the bottom. From here turn left and cross the bridge over the Nant Llech and walk up the wooden staircase to join the path. The waterfall is two minutes from here. Return to the car park by the same route.