As the United States Geological Survey explains, the rocks at the core of the Appalachian mountains formed more than a billion years ago when North America and South America merged together. However, the mountains did not form at all once; they would pop up but erode over time (via Mental Floss). This cycle continued and as one mountain set crumbled another would emerge.

Today, the topography of the Appalachian Mountains is about 20 million years old. According to West Virginia Public Broadcasting, some areas of the Applachians are made up of rocks that are approximately 1.2 billion years old.

These, however, are not the oldest rocks on earth; those can be found in Canada and Greenland (at about 4 billion years old). Nonetheless, the Appalachian Mountains are distinct. Thanks to their continuing rebirth through their billion-year lifetime, they are simultaneously young and old.

With its vast beauty and fauna, one can enjoy the mountain’s offerings by hiking the Appalachian Trail. Per Discover Walks, it is said to be the longest in America. However, it’s also an incredibly difficult hike. Although 3 million people walk parts of the trail each year, only 10 to 15% of people who start make it through all the way.