The Afon Mawddach is a river in Gwynedd, Wales, which has its source in a wide area SH820300 north of Dduallt in Snowdonia. It is 28 miles (45 km) in length, and is much branched; many of the significant tributaries are of a similar size to the main river. The catchment area is bounded to the east by the Aran Fawddwy massif and to the west and north by the Harlech dome which forms a watershed just south of Llyn Trawsfynydd.

The Rhinogydd are a range of mountains located east of Harlech in North Wales. The name Rhinogydd derives from the names of two of the more famous peaks, Rhinog Fawr and Rhinog Fach, although the greatest elevation in the range is reached by Y Llethr, 756 m.