Canisp has little vegetation, even on its lower slopes large areas of Gneiss (one of the oldest rocks in the world) are visible on the surface.

Canisp was formed when surrounding rocks were eroded during an episode of glaciation, while the ridge was left poking above the level of the ice sheet, as a nunatak.

Canisp is less visited than the nearby smaller mountain of Suilven, with its famous jagged summit ridge, which stands five kilometres (3 mi) to the west and is 116 metres (381 ft) lower in elevation.

This is the shortest and quickest route, but it is still six kilometres (3+1⁄2 mi) long, almost completely devoid of paths, and defended by stones, heather and bog.

The route from Lochinver gains the northwest ridge by a path from Loch na Gainimh and is regarded by Hamish Brown as the most pleasing way up the mountain.