Geology
Y Garn Goch is formed from the coarse sandstones of the Ffairfach Grit Formation of the early Ordovician period. A northeast-southwest oriented anticline (the Garn Goch Anticline) which runs through Y Garn Goch can be seen to fold these rocks. The sandstones and mudstones of the Abergwili and Llandeilo Flags Formations form the lower slopes of the hill to north and south. A fault runs northeast-southwest through the col between the two tops and is considered a part of the Welsh Borderland Fault System. The lower ground is mantled by glacial till, a legacy of the last ice age when the valley was filled by the Towy Valley glacier. The hill lies within Fforest Fawr Geopark designated in respect of the outstanding geological heritage of the region.
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