The geology of the Cairngorms was created on a timeline that stretches back hundreds of millions of years. Much of the land is underlain by granite that formed deep within the Earth's crust and 'surfaced' as the overlying layers of rock were stripped away by ice, wind and water. The bedrock is hard, and although the area has been heavily glaciated, still boasts 18 Munros, the highest of Scotland's peaks. The area attracts climbers, walkers and assorted adventurers who want to pit themselves against some of the most challenging conditions to be found anywhere in the UK. The plants and animals of the Cairngorms need to be hardy to survive the severe winter conditions. The higher reaches of the mountains are rich in montane vegetation such as lichen-rich heath and other habitats support many rare species.