Hatterrall Hill is a rounded peak in the Black Mountains which sits on the Wales-England border, partly in Monmouthshire, Wales and partly in Herefordshire, England. Its summit at 531m is the high point of a peaty plateau which falls away steeply on all sides. Broad ridges run to the north, the southeast and southwest. To the north the ridge (known as Hatterrall Ridge) dips to a col at around 485m elevation before rising gradually over several kilometres towards Crib y Garth / Black Hill and Hay Bluff. The ridge to the southwest ends abruptly at the sheer cliff known as the Darren below which is a considerable landslipped area extending south to the hamlet of Cwmyoy with its mis-shapen church. The Welsh part of the hill falls within the Brecon Beacons National Park.
The hill is composed from sandstones and mudstones of the Senni Beds Formation of the Old Red Sandstone which is of Devonian age. Numerous small quarries adorn its slopes though all are now abandoned. The Vale Of Ewyas was occupied by glaciers during the ice ages though the plateau was probably ice-free.