Two other large corries stand to the west of the summit, Coire a’ Chaolain on the northern side of the west ridge and Coire Ghabhar on the southern side, these two corries almost touch and make the ridge quite narrow. Drainage from the mountain finds its way to both the east and west coasts of Scotland, the northern slopes drain via the River Etive and Loch Etive to the west coast near Oban. Water from the southern slopes goes to the same place but progresses by Glen Orchy and Loch Awe while the eastern slopes drain via Loch Rannoch and the River Tay to the east coast at the Firth of Tay. The whole of the Black Mount range is noted for the complexity of its geology, there is a junction of gneiss and Cruachan granite near the summit of Stob Ghabhar.