The Dwyryd, Mawddach and Dyfi Estuaries, and 23 miles (37 kilometres) of coastline also contribute to the excitingly varied landscapes which are home to a wide range of wildlife.
Snowdonia is classic ground for the study of geology; the setting in the 19th century for the first scientific investigations of some of the world's oldest rocks. Building on those early studies, geologists have been able to piece together a very full description of its creation over the course of hundreds of millions of years of submersion, lifting and erosion.
Snowdonia's geology consists of four different types of rocks - the Pre-Cambrian, the Cambrian, the Ordovician and the Silurian - even the youngest of which, the Silurian, is over 400 million years old.
Detail was added to the landscape, in geological terms, relatively recently, by the Great Ice Age. The last of the glaciers did not disappear until about 10,000 years ago, and their relics are abundant in the National Park, in the form of u-shaped and hanging valleys, erratic boulders, cirques, moraines and glacial lakes.