Mynydd Machen

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Mynydd Machen
Mynydd Machen trig point - - 3001553.jpg
Trig point at the summit
Summit: 1,188 ft ST224900
51°36’13"N, 3°7’20"W

Mynydd Machen is a 1,188-ft-high hill in Monmouthshire lying between the town of Risca and the village of Machen. Its summit is crowned by a trig point and a mast.


The hill lies at the south-eastern extremity of the South Wales Coalfield where the varied Carboniferous Period rock strata of the coalfield margin are tilted steeply north-westwards into the coalfield basin. The sequence which outcrops on Mynydd Machen in north-east - south-west aligned bands is this (oldest at base):

Warwickshire Group

  • Pennant Sandstone Formation
  • Brithdir Member
  • Rhondda member
  • Deri Member

South Wales Coal Measures Group

  • South Wales Middle Coal Measures Formation
  • South Wales Lower Coal Measures Formation

Marros Group

  • Bishopston Mudstone Formation
  • Twrch Sandstone Formation

Pembroke Limestone Group

The summit of the hill is formed from the sandstone of the ‘Brithdir Member’ of the Pennant Sandstone Formation. A large quarry towards the south of the hill works the dolomitic limestone of the Pembroke Limestone Group.[1][2]


Numerous public footpaths criss-cross the hill, some being followed by promoted recreational walking routes such as the Rhymney Valley Ridgeway Walk, the Sirhowy Valley Walk and the Raven Walk. The upper slopes of the hill and most of the woodland which clothes its slopes is mapped as open access under the Countryside and Rights of Way Act 2000 and thereby open to access on foot by the public.[3]


  1. British Geological Survey 1:50,000 map sheet 249 Newport & accompanying memoir
  2. BGS ‘Geology of Britain’ viewer
  3. Ordnance Survey Explorer map 152 Newport & Pontypool

Outside links