Cefn y Brithdir is the name given to the broad ridge of high ground between the

Rhymney Valley The Rhymney Valley () is one of the South Wales valleys, with the Rhymney River forming the border between the historic counties of Glamorgan and Monmouthshire. Between 1974 and 1996 a Rhymney Valley local government district also existed (one o ...

(

Welsh Welsh may refer to: Related to Wales * Welsh, referring or related to Wales * Welsh language, a Brittonic Celtic language spoken in Wales * Welsh people People * Welsh (surname) * Sometimes used as a synonym for the ancient Britons (Celtic peop ...

: Cwm Rhymni) and Cwm Darran in the Valleys region of 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 ...

. It lies within the unitary area of

Caerphilly Caerphilly (, ; cy, Caerffili, ) is a town and community in Wales. It is situated at the southern end of the Rhymney Valley. It is north of Cardiff and northwest of Newport. It is the largest town in Caerphilly County Borough, and lies wit ...

. The northwest–southeast aligned ridge whose top surface is plateau-like, achieves a height of 477m at the summit of Pen Garnbugail (OS grid ref SO 100037). There are significant subsidiary tops of 446m to the southeast at OS grid ref SO 114049 and, to the north, of just over 460m at Mynydd Fochriw (OS grid ref SO 099047). To the south it drops away to the confluence of the Nant Bargod Rhymni with the

Rhymney River The Rhymney River ( cy, Afon Rhymni) is a river in the Rhymney Valley, South Wales, flowing through Cardiff into the Severn Estuary. The river formed the boundary between the historic counties of Glamorgan and Monmouthshire until in 1887, t ...

. To the northwest it falls to a broad saddle at around 360m between

Pontlottyn Pontlottyn ( cy, Pontlotyn) is a village located in the county borough of Caerphilly, within the historic county boundaries of Glamorgan, Wales. It is sited just to the south of Rhymney, and to the west of the Rhymney River. History Pontlottyn, ...

and

Fochriw Fochriw () is a village located in Caerphilly County Borough, Wales, United Kingdom. It was well known for its neighbouring collieries Coal mining is the process of resource extraction, extracting coal from the ground. Coal is valued for i ...

. Much of its western flanks are afforested with conifer plantations. There are numerous cairns, house platforms and other archaeological features scattered across the area. A

Roman road Roman roads ( la, viae Romanae ; singular: ; meaning "Roman way") were physical infrastructure vital to the maintenance and development of the Roman state, and were built from about 300 BC through the expansion and consolidation of the Roman Re ...

is recorded as crossing the eastern slopes of Pen Garnbugail.

Geology

The entire hill is composed of sandstones and mudstones dating from the

Carboniferous Period The Carboniferous ( ) is a Period (geology), geologic period and System (stratigraphy), system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago (Myr, Mya), to the beginning of the Permian Period, ...

. There are also numerous

coal seam Coal mining is the process of extracting coal from the ground. Coal is valued for its energy content and since the 1880s has been widely used to generate electricity. Steel and cement industries use coal as a fuel for extraction of iron from ...

s within the sequence, most of which have been worked. The upper part of the hill including the summit plateau is formed from the

Pennant Sandstone The Pennant Measures is the traditional name for a sequence of sedimentary rocks of the South Wales Coalfield. They were also referred to as the Upper Coal Measures and assigned to the Westphalian 'C' and Westphalian 'D' stages of the Carbonifero ...

, a rock assigned to the Carboniferous Upper Coal Measures. The flanks of the hill owe their steepness in part to the action of

glacial ice A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its Ablation#Glaciology, ablation over many years, often Century, centuries. It acquires dis ...

during the succession of

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 ...

Access

A minor public road runs along the southern half of the ridge and this route is followed by the

Rhymney Valley Ridgeway Walk The Rhymney Valley Ridgeway Walk is a waymarked long distance footpath in the UK forming a circular walk in the Rhymney Valley area of South Wales.open country "Open Country" is a designation used for some UK access land. It was first defined under the National Parks and Access to the Countryside Act 1949 (and extended by the Countryside Act 1968), and was land over which an appropriate access agreeme ...

under the

CRoW Act The Countryside and Rights of Way Act 2000 (c. 37), known informally as the CRoW Act or "Right to Roam" Act is a United Kingdom Act of Parliament affecting England and Wales which came into force on 30 November 2000. Right to roam The Act imp ...

thus giving a right of access to walkers. Similar rights apply to many of the afforested areas. There are a number of

public footpath A footpath (also pedestrian way, walking trail, nature trail) is a type of thoroughfare that is intended for use only by pedestrians and not other forms of traffic such as motorized vehicles, bicycles and horses. They can be found in a wide ...

s and other

public rights of way Right of way is the legal right, established by grant from a landowner or long usage (i.e. by prescription), to pass along a specific route through property belonging to another. A similar ''right of access'' also exists on land held by a gov ...

over the hill.Ordnance Survey 1:25,000 scale Explorer map series sheet no 166''Rhondda & Merthyr Tydfil/Merthyr Tudful''

References

{{coord, 51.726, -3.261, dim:3000_region:GB, display=title Mountains and hills of Caerphilly County Borough Caerphilly Sites of Special Scientific Interest in Caerphilly County Borough