Cefn Cil Sanws is a hill in the

Brecon Beacons National Park The Brecon Beacons National Park ( cy, Parc Cenedlaethol Bannau Brycheiniog) is one of three national parks in Wales, and is centred on the Brecon Beacons range of hills in southern Wales. It includes the Black Mountain (range), Black Mountain ...

within the

county borough County borough is a term introduced in 1889 in the United Kingdom of Great Britain and Ireland, to refer to a borough or a city independent of county council control, similar to the unitary authorities created since the 1990s. An equivalent ter ...

Merthyr Tydfil Merthyr Tydfil (; cy, Merthyr Tudful ) is the main town in Merthyr Tydfil County Borough, Wales, administered by Merthyr Tydfil County Borough Council. It is about north of Cardiff. Often called just Merthyr, it is said to be named after Tydf ...

in south

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

. 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 nomenclature varies regionally: they a ...

. 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 period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...

age all tilted moderately to the south. The summit is formed from

Carboniferous Limestone Carboniferous Limestone is a collective term for the succession of limestones occurring widely throughout Great Britain and Ireland that were deposited during the Dinantian Epoch of the Carboniferous Period. These rocks formed between 363 and ...

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 in South Wales. These rocks were formerly known as the Millstone Grit Series but are now distinguished from the similar but geographi ...

(formerly known as the 'Basal Grit' of the Millstone Grit 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 pavement. The term is mainly used in the UK and Ireland, where many of these landforms have developed dist ...

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 ...

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 gree ...

Plants

Much of the hill is owned and managed by the

Brecknock Wildlife Trust Brecknock Wildlife Trust ( cy, Ymddiriedolaeth Natur Sir Frycheiniog) 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 ...

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, or features of geological or ...

. The steep cliffs of Darren Fach on the western side are the home to Britain's rarest tree -

Ley's Whitebeam ''Sorbus leyana''. Ley's whitebeam, is a species of small tree which is endemic to two sites in southern Wales. It is thought to have arisen by hybridisation of two species of ''Sorbus'', one of which was the rowan. Its closest relatives are so ...

(''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 Rigid or rigidity may refer to: Mathematics and physics *Stiffness, the property of a solid body to resist deformation, which is sometimes referred to as rigidity *Structural rigidity, a mathematical theory of the stiffness of ensembles of rig ...

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 t ...

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 ...

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