The Community includes the hamlet of Crai itself, the scattered settlements of Felin-crai and Cwm Crai together with those of Cwm Treweryn.

The lie of the land

Crai Community ranges in height from just under 190m above sea level downstream of Pantysgallog on the Usk to the summit of Fan Gyhirych at 725m (SN 880190).  Other notable summits include:

• twin summits of Fforest Fach 381m & 382m (SN 906277 & 908264)
• Fan Bwlch Chwyth 603m (SN 912216)
• Fan Fraith 668m (SN 887183)

The Community is drained by the River Usk into which flows the Afon Crai and its tributaries Rhuddnant, Nant Cnewr-fawr, Nant Cnewr-fach and Nant Gyhirych.  The eastern area is drained by the Treweryn.

Old Red Sandstone

The Community is wholly underlain by Old Red Sandstone rocks. These are largely the mudstones and siltstones of the St Maughan's Formation to the north of Cray Reservoir incorporating some sandstones as seen in the quarry on the eastern side of Fforest Fach.  The higher hills to the south are composed of the sandstones of the Senni Formation topped by the similar Brownstones Formation.  The very summit of Fan Gyhirych is formed from the harder-wearing Plateau Beds.

A number of geological faults cross the area, largely aligned NE-SW, some of which seem to have had an influence on the development of valleys such as Cwm Treweryn.  The Swansea Fault aligns itself with the road from Penwaundwr to Gelli Cottage and then south to Bwlch Bryn-rhudd.

Legacy of the Ice Ages

The NE-facing cwm of Fan Gyhirych is clearly of glacial origin.  The pass of Bwlch Bryn-rhudd is a major breach in the E-W watershed of Fforest Fawr and one over which ice will have passed.  Much of the lower ground within the community is plastered with glacial till and hummocky ground composed of clayey gravel is common.

There are traces of landslips in several locations.

Archaeology

The most striking feature is the Iron Age hillfort of Twyn-y-gaer.  There is a scatter of cairns and standing stones together with a number of pillow mounds above Cray Reservoir.

Maps

Geology

Sheets 213 'Brecon' and 231 'Merthyr Tydfil' of the British Geological Survey’s 1:50,000 map series of England and Wales give full coverage of both the bedrock geology and superficial deposits of the Community area. BGS publishes a 'memoir' and a 'sheet explanation' to accompany these maps.

General

The following Ordnance Survey maps cover the Community:

• Landranger sheet 160 'Brecon Beacons' (1:50,000 scale)
• Explorer sheet OL12 'Brecon Beacons National Park/Western area' (1:25,000 scale)

Public transport

Bus services operate along the A4067 road from Ystradgynlais to Sennybridge.  The nearest railway stations are at Llandovery on the Heart of Wales railway line and at Merthyr Tydfil and Aberdare to the south.

See Traveline Cymru for bus and train services including stops, timetables and route-planning information.