For detailed geological maps of Torridon, please look at these British Geological Survey's map-viewer sites, for the western half of the area ("Torridon" sheet) and eastern half ("Lochcarron" sheet).
Torridon Exhibition (C&D): A brief note about Torridon's rocks
In Torridon, the effect of the geology on the landscape is very striking.
Above Diabaig and across the Narrows between Upper and Outer Loch Torridon, the Lewisian Gneiss is some of the oldest rock in the world - formed about 3,000 million years ago. It forms a very distinctive landscape known as "Cnoc and Lochan" - myriad rounded hillocks and hollows full of water. Walking in gneiss areas can make for tricky navigation and much up and down, but also a remarkable feeling of seclusion. Photo 17a shows an example of complex gneiss topography.
The predominant rock type is Torridonian Sandstone - a very hard, reddish, blocky sandstone, which forms the strong horizontal lines in the landscape that you can see clearly on Liathach, Beinn Damh, Beinn Shieldaig and other mountains. Torridonian rocks form the bulk of most of the hills here, the layers often forming towering crags and precipices. You can see this on several of the photos, e.g. 35, 40 and 43.
The Gaelic names of the mountains reflect the geology too - for example, Maol Chean-dearg translates as "Bald Red Head", referring to the red sandstone at the top. The Torridonian here is mainly between 800 and 1,000 million years old.
The younger Cambrian quartzite formations show as white tops to some mountains, such as Beinn Eighe. Close up, as with all the rocks, there is much subtle variation in colour. The Gaelic name Beinn Liath Mhòr translates as "The big grey hill" and from Torridon the quartzite hills high above the head of the Loch do indeed look distinctively grey. In some places the rock has a pinkish colour - see for example photo 14. Photos 5 and 26 also feature quartzite.
The quartzite is typically in the region of 500 million years old. In places they include the distinctive "pipe" rock - fossilised remains of ancient worm burrows.
There is a small amount of limestone to the south of the area: the Rassal Ashwood, near the road at Tornapress, is the main part. There are small areas of surface rock and some typical limestone flora.