The mountain is mostly made of Torridonian sandstone. Like the peaks around Torridon (for which the rock is named), An Teallach has terraced sides riven with steep gullies and a sharp rocky summit crest at Sgùrr Fiona. The steepest section, known as Corrag Bhuidhe, rises above Loch Toll an Lochain. Corrag Bhuidhe's most spectacular feature is an overhanging pinnacle known as Lord Berkeley's Seat.