GeoGraph - photograph every grid square

The gorge of the Nant Dropyns has formed because the original stream bed (running west-east) was cut up by a glacier flowing south-north, resulting in the stream cascading (SN8794 : Ffrwd Fawr) sideways into the glacial trough (SN8793 : Pen Cwm Twymyn). The sudden drop has resulted in a fast-flowing stream digging into the hillside above the waterfall. The Nant Dropyns and the Nant Bryn-moel merge in the background of this picture, and the waterfall is another 500m downstream.