Crug Mawr is a hill in the Black Mountains

Black Mountains, Wales

The Black Mountains are a group of hills spread across parts of Powys and Monmouthshire in southeast Wales, and extending across the national border into Herefordshire, England. They are the easternmost of the four ranges of hills that comprise the Brecon Beacons National Park, and are frequently...

 in the Brecon Beacons National Park in southern Powys

Powys

Powys is a local-government county and preserved county in Wales.-Geography:Powys covers the historic counties of Montgomeryshire and Radnorshire, most of Brecknockshire , and a small part of Denbighshire — an area of 5,179 km², making it the largest county in Wales by land area.It is...

, Wales

Wales

Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...

. Its summit at a height of 550m (1,805ft) is marked by a trig point

Trig point

A triangulation station, also known as a triangulation pillar, trigonometrical station, trigonometrical point, trig station, trig beacon or trig point, and sometimes informally as a trig, is a fixed surveying station, used in geodetic surveying and other surveying projects in its vicinity...

. The peak sits high above the valleys of the Grwyne Fawr

Grwyne Fawr

The Grwyne Fawr is a river in the Brecon Beacons National Park in south Wales. A section of it forms the administrative border between Powys and Monmouthshire and also of the historic counties of Brecon and Monmouth. The river and its major tributary the Grwyne Fechan flow into the River Usk at...

 and Grwyne Fechan to the north of the more well-known Sugar Loaf. The views from here across the Black Mountains are wide ranging and also extend eastwards across Monmouthshire

Monmouthshire

Monmouthshire is a county in south east Wales. The name derives from the historic county of Monmouthshire which covered a much larger area. The largest town is Abergavenny. There are many castles in Monmouthshire .-Historic county:...

. Four ridges run off to the northwest, east, southeast and southwest, the last ending in the subsidiary summit of Blaen-yr-henbant.

Access

All of the upper slopes of the hill are designated as open country. A bridleway runs up from the minor road east of Llanbedr

Llanbedr, Crickhowell

Llanbedr is a hamlet northeast of Crickhowell in the county of Powys in south Wales. It lies above the river known as the Grwyne Fechan just above its confluence with the Grwyne Fawr in the southern reaches of the Black Mountains range. The hamlet lies within the shadow of Table Mountain, an...

 and then on northwards to Mynydd Du Forest. The Beacons Way runs across the slopes of the hill between Partrishow

Partrishow

Partrishow, also known as Patricio or Patrishow, is a small village in the Black Mountains of South Wales, within the Brecon Beacons National Park.-Location:...

 and Llanbedr.

Geology

In common with other hills in the Black Mountains, Crug Mawr is formed from mudstones and sandstones of the Old Red Sandstone

Old Red Sandstone

The Old Red Sandstone is a British rock formation of considerable importance to early paleontology. For convenience the short version of the term, 'ORS' is often used in literature on the subject.-Sedimentology:...

 laid down during the Devonian period but there is little rock exposed at the surface other than in the beds of the streams which occupy valleys such as Cwm Milaid and Cwm Beusych.