Cader/Cadair Idris is a spectacular mountain reserve with a variety of landscapes and terrain. Rugged summits, glacial lakes and a mossy wooded gorge cover over 450 hectares of breathtaking landscape.
Local folklore describes Idris as a giant who lived on this magnificent mountain. The large boulders on the lower slopes are said to be the debris of stone throwing battles between Idris and other giants. Idris is more likely to have been an important leader in this area, a giant in personality and authority rather than in stature.
The reserve lies within Snowdonia National Park and is part of the Cadair Idris Special Site of Scientific Interest (SSSI) and Special Area of Conservation (SAC).
The site encompasses the mountain and lower slopes, with a variety of habitats of European importance. These include dry heath, wet heath, blanket bog, woodland and the species-rich marshy grasslands of Tir Stent common, as well as a number of low nutrient or clear-water lakes. The cliffs support tall herbs growing on the ledges, and a range of plants growing on rock crevices. These habitats support a wide range of species, including slender green feather-moss and marsh fritillary Butterfly.
While the romantically inclined attribute its features to the work of giants, geologists come up with more prosaic but nonetheless interesting explanations that span hundreds of millions of years. The origin of the rock is volcanic, some of the lavas being poured out under the sea and shaped into bulbuous "pillows" that give it the name pillow lava. These are interspersed with layers of ash and other sediments that settled out on the sea bed of the time.
The glaciers of the last ice age scoured and scraped at this hard upfolded rock leaving visible scratches on some of the surfaces and hollowing out basins now filled with small lakes such as those at Cregennan on the first 'step' up the mountain, or the supposedly bottomless Llyn Cau on the south side.
Amongst this craggy country on the mountain tops there survive rare arctic/alipne flowers, a legacy of the last Ice Age such as purple saxifrage and least willow (a 'tree' that never gets to more than a scrambling shrub).
At the lower level around Cregennan the National Trust owns two small hill farms where the rough grazing can be managed in the traditional way. A sign of summer here is the arrival of that dainty visitor, the wheatear, often difficult to spot until it displays its white rump in flight.