Geologically Beinn Liath Mhòr is made up of Cambrian quartzite scree and Torridonian sandstones giving the mountain a distinctive colour contrast of light and dark.

The mountain's other main characteristic is its two-kilometre-long undulating summit ridge which does not drop below 800 metres for its entire length.

This culminates at the summit at its far western end at a height of 926 metres (3038 feet) making Beinn Liath Mhòr the 258th highest Munro.

The most common approach to Beinn Liath Mhòr starts at Achnashellach on the A890 road and goes by the right of way to Glen Torridon.

It is also possible to climb Beinn Liath Mhòr from Glen Torridon starting at the car park at grid reference NG957568 and following the Ling path to its termination and then ascending the mountain by its western ridge.