Cefn Cil Sanws is a hill in the

Brecon Beacons National Park Brecon Beacons National Park, officially named Bannau Brycheiniog National Park (), is a National parks of the United Kingdom, national park in Wales. It is named after the Brecon Beacons (), the mountain range at its centre. The national park ...

within

Merthyr Tydfil County Borough Merthyr Tydfil County Borough () is a Principal areas of Wales, county borough in the South East Wales, south-east of Wales. In , it had an estimated population of , making it the smallest local authority in Wales by population. It is located in ...

in south

Wales Wales ( ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by the Irish Sea to the north and west, England to the England–Wales border, east, the Bristol Channel to the south, and the Celtic ...

. The summit at 460m above sea level is crowned by a

trig point A triangulation station, also known as a trigonometrical point, and sometimes informally as a trig, is a fixed surveying station, used in geodetic surveying and other surveying projects in its vicinity. The station is usually set up by a map ...

. The steep cliffs of Darren Fawr and Darren Fach defend its western side which drops down into Cwm Taf. A major limestone quarry is worked on the southeastern side of the hill. An unexpected feature at this altitude is Merthyr Tydfil Golf Course which extends high onto the eastern and southern slopes of the hill.

Geology

Western scree slopes of Cefn Cil-Sanws - geograph

The hill is composed of a layer cake of rocks of

Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...

age all tilted moderately to the south. The summit is formed from Carboniferous Limestone whilst outcrops of

Twrch Sandstone The Marros Group is the name given to a suite of rocks of Namurian age laid down during the Carboniferous period (geology), Period in South Wales. These rocks were formerly known as the Millstone Grit, Millstone Grit Series but are now distinguish ...

(formerly known as the 'Basal Grit' of the

Millstone Grit Millstone Grit is any of a number of coarse-grained sandstones of Carboniferous age which occur in the British Isles. The name derives from its use in earlier times as a source of millstones for use principally in watermills. Geologists refer to ...

Series) can be seen to the north and on its steep western flanks. There are sections of

limestone pavement A limestone pavement is a natural karst landform consisting of a flat, incised surface of exposed limestone that resembles an artificial Sidewalk, pavement. The term is mainly used in the UK and Ireland, where many of these landforms have devel ...

on the tilted plateau surface and small crags and pavements of gritstone to their south. The latter show evidence of

glacial striations Glacial striations or striae are scratches or gouges cut into bedrock by glacial abrasion. These scratches and gouges were first recognized as the result of a moving glacier in the late 18th century when Swiss alpinists first associated them w ...

suggesting that the hill was over-ridden by ice moving southwards from the central Beacons during the

ice ages An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages, and Gre ...

Plants

Much of the hill is owned and managed by the

Brecknock Wildlife Trust Brecknock Wildlife Trust () is a former wildlife trust covering the vice county of Brecknockshire in Wales. The Trust was founded in 1964, with a network of volunteers carrying out most of its work. No full-time conservation officers were in po ...

as a

nature reserve A nature reserve (also known as a wildlife refuge, wildlife sanctuary, biosphere reserve or bioreserve, natural or nature preserve, or nature conservation area) is a protected area of importance for flora, fauna, funga, or features of geologic ...

. The steep cliffs of Darren Fach on the western side are the home to Britain's rarest tree - Ley's Whitebeam (''Sorbus leyana'') - the larger part of the country's population of these trees being found on this one cliff. Also of interest is the rare rigid buckler fern which clings to the scree slopes on this western flank.

Access

Most of the hill is open country. A public footpath and a bridleway at its southern end provide access from the

A470 road The A470 (also named the Cardiff to Glan Conwy Trunk Road) is a trunk road in Wales. It is the country's longest road at and links the capital Cardiff on the south coast to Llandudno on the north coast. While previously one had to navigate th ...

and from

Cefn-coed-y-cymmer Cefn-coed-y-cymmer () is a small community on the northwestern edge of Merthyr Tydfil County Borough in Wales. It is situated in the neck of land between the rivers Taf Fawr and Taf Fechan at their confluence (Welsh: 'cymer'). The village lies w ...

References

External links

Brecknock Wildlife Trust's Darren Fawr nature reserve
{{coord, 51.7821, -3.4146, type:mountain_region:GB, display=title Brecon Beacons Mountains and hills of Merthyr Tydfil County Borough