Black Mountain
Twyn Llech (Welsh)
The summit, crossed by the Offa's Dyke Path
Highest point
Elevation	703.6 m (2,308 ft)
Prominence	155 m (509 ft)
Parent peak	Waun Fach
Listing	Marilyn, Hewitt, County Top, Nuttall
Coordinates	52°00′30″N 3°05′08″W / 52.00847°N 3.0855°W / 52.00847; -3.0855
Geography
Black Mountain Herefordshire, England / Brecknockshire, Wales
Parent range	Black Mountains
OS grid	SO255350
Topo map	OS Landranger 161
Climbing
Easiest route	The Cat's Back

The Black Mountain (Welsh: Twyn Llech), is a mountain in the Black Mountains. It is the only Marilyn to fall exactly on the Welsh–English border, Powys and Herefordshire. Its parent peak, Waun Fach, lies to the west.

Access

The Black Mountain is the highest point on Hatterrall Ridge. Offa's Dyke Path passes along the ridge, more or less from south to north. A steeper path leads to the summit from near the former youth hostel in the Vale of Ewyas to the west. The summit is unmarked and, because of the very shallow gradients along the summit ridge, virtually impossible to determine in situ. Open access to all the moorland here means that deviation from the paths is allowed. The ground is peaty and normally very wet even in good weather, especially on the highest ground.

It is the highest summit in England south of Great Whernside in the Yorkshire Dales,^[1] even though higher neighbours are very close by in Wales. However, some mountain lists, such as the Nuttalls, consider the mountain belongs only to Wales, due to the Black Mountains range being principally a Welsh massif.^[2]

Geology

The mountain is composed of sandstones and mudstones of the Senni Formation of the Old Red Sandstone which is of Devonian age. The shape of the Vale of Ewyas to the south and west of the Hatterall ridge strongly suggests that it was occupied by a glacier during at least one ice age, though not perhaps during the last ice age.^[3] The plateau was probably ice-free.