This nature reserve is a 2.5km stretch of dramatic wooded limestone gorge cut by the River Taf Fechan, between the bridges of Pontsarn and Cefn Coed to the North of Merthyr Tydfil.
It lies adjacent to the eastern side of the popular Taff Trail and the reserve incorporates much of the area notified as Cwm Taf Fechan Woodlands Site of Special Scientific Interest.
The reserve, managed by the Wildlife Trust of South and West Wales, has high nature conservation value and supports uncommon flora and fauna.
On the western bank of the river you can see a good population of broad leaved helleborine, as well as small-leaved lime. In addition, there are large areas of grazed limestone grassland, some with bracken, with plentiful violets providing a suitable habitat for silver-washed fritillary butterflies.
The Eastern bank sees a number of springs, with Tufa deposits, and the Gurnos quarry face is well developed, with facies and caves likely to be home to bats.
The reserve has a wide diversity of habitats, fast and slow-flowing freshwater, open and dense deciduous woodland; calcareous and acidic grassland; exposed limestone cliff faces and old walls and tufa springs.
Signs of otters are regularly spotted, and the whole river stretch supports birds such as dipper and grey wagtail. Goosander are regular in Winter, and evidence of badgers are often seen.
The gorge was created by the young Taf Fechan river cutting into the northern outcrop of carboniferous limestone, forming the northern border of the South Wales coalfield.
A particularly impressive section is to the east of the Trefechan estate. The geology is especially obvious in the Gurnos quarry.
South of the quarry, millstone grit is the underlying rock. At the site of the Heads of the Valleys road bridge there are fallen blocks of honeycomb sandstone, the marker horizon which occurs at the S zone / D zone boundary in the carboniferous limestone over a wide area of the north crop of the coalfield.
The sandstone outcrops at the top of the vertical face south of the Gurnos quarry cliff. The majority of the site, to the north of the road bridge, consists of the Cil yr Ychen series of carboniferous limestone. This is richly fossiliferous, with brachiopods (typically seminula), productids, corals and gastropods (including Euomphalus).
The Pont Sarn bridge by the Blue Pool (Pont-sarn-hir - the bridge of the long paved road) is the site of the Roman road crossing, travelling from Y Gaer at Brecon to the coastal fort at Cardiff. From the bridge, it went through Gurnos, towards Penydarren Park and on to Gelligaer.
There are the remains of an 18th-century corn mill on the eastern bank of the northernmost section of the reserve, one of four grinding mills that were located in the Taf Fechan valley. The original millstone grit millstone is nearby.
Further down the river are the remains of a fullers mill (a pandy) on the western bank just north of the timber bridge. Well-known local weavers, the Harris family, owned both these mills.
The Gurnos quarry supplied limestone for the furnaces of the Cyfarthfa Ironworks. Following the closure of the Ironworks, the quarry was planted with a selection of pine trees, with some still surviving on top of the cliff.
The tramway runs south from the quarry alongside the Taff, to beyond the Cefn Coed bridge. It was extended to reach the new Glamorganshire canal in 1792. It supplied the Cyfarthfa Ironworks with the all-important limestone needed for the ironworking process, and the stones forming the base of the tramway rails are a scheduled ancient monument, as is the Cyfarthfa leat which runs alongside it.
We have created new information packs to help explain the landscape you'll be travel through and the benefits it brings. Find out more about the flora and fauna you can expect to see or learn about the history that surrounds the many heritage sites you'll pass on your journey. Download your information maps below.
We hope you enjoy the Taff Trail by whatever means you've chosen, but please travel responsibly. Take care of yourself, your surroundings and each other. Download your information leaflets below.
If you are traveling through Merthyr Tydfil along Taith Taf (from south to north,) download our latest map to assist you
Alongside Treasuring our Trails we have a responsibility to ensure we, as custodians, maintain them for generations to come. Please respect the countryside and each other.
You can find more information and guidance by following the links below:
The Taf Fechan Nature Reserve Circular Walk is just one of a series of trails running right through the county borough that encapsulates the area's history complemented by miles and miles of natural beauty. So, if you want to take time to stop at one of our amazing adventure attractions, learn about our history, shop, eat, sleep or just take a moment to savour the breath-taking scenery. Merthyr has it all.
© Merthyr Tydfil County Borough Council 2025