Cefn yr Ystrad is a mountain in the Brecon Beacons National Park in Wales. It is an outlier of the Central Beacons group. The broad northeast - southwest aligned ridge reaches an elevation of 617 metres (2,024 ft). One of the southernmost peaks in the Brecon Beacons, it rises to the east of Pontsticill Reservoir. The summit area is a great stretch of wild moorland, with the highest point marked by a trig point.