The mountain is made up of schist rocks of the Dalradian group, with outcrops of pink granite on the mountain's upper slopes. The south side of the mountain has a broad shelf at a height of around 450 metres, the result of lateral erosion by glaciers in the Ice Age. Rainfall on Meall Glas drains to the east coast of Scotland via the glens of Dochart (south) or Lochay (north) and then by Loch Tay and the River Tay.