Mynydd Bwlch-y-groes

Mynydd Epynt (Welsh: [ˈmənɨð ˈɛpɨnt]) is an upland area of Mid Wales within the county of Powys, Wales. It is bounded to the south by the upper section of the valley of the River Usk, and the Brecon Beacons National Park. It is bounded to the north by the valley of the Afon Irfon and to the east by the valley of the River Wye. Its western boundary is less distinct but lies eastward of the A483 Llandovery to Llanwrtyd Wells road. Its character is that of an extensive though dissected moorland plateau lying between 400 and 450m above sea level and whose highest point of 478m (1,568 ft) is reached at an unnamed rise at OS grid ref SN 961464.

The south-western part of Mynydd Epynt is known as Mynydd Bwlch-y-groes. The area is drained by several southward-flowing rivers which empty into the River Usk. These include (from west to east) the Cilieni, Nant Bran, Afon Ysgir (with its two headwaters the Ysgir Fechan and Ysgir Fawr) and Afon Honddu. The Duhonw drains north-eastward into the River Wye. The highest point is a Marilyn (having topographic prominence of at least 150m).

The Welsh-language name means mountain (crossed by a) horse-path. It is often misspelt as Mynydd Eppynt. In earlier times it was known simply as Epynt and is commonly referred to today as 'the Epynt'.

Mynydd Epynt is largely formed from the Raglan Mudstone Formation and the St Maughans Formation of the Old Red Sandstone laid down during the latest part of the Silurian period and the succeeding Devonian period though there is little in the way of rock exposures at the surface. The northern and western escarpment of Mynydd Epynt is formed from a suite of rocks assigned to the Ludlow stage of the late Silurian and which include the Temeside Mudstone, the Tilestones, the Cae'r Mynach, Fibua, Aberedw, Cwm Craig Ddu and Irfon Formations. These consist variously of sandstones, mudstones and siltstones.

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