The Appalachians are a scar of plate tectonics. When ancient continents collided to form the supercontinent Pangaea, the crumple zone between them pushed up a spine of stone that stretched from what is now Morocco through Scotland to Alabama. North Africa's Atlas range and Scotland's Highlands are cousins, separated only when Pangaea split open and the Atlantic flooded the gap roughly 180 million years ago. The ridges you see today are the roots of mountains, exposed by erosion deep enough to reveal rocks that once lay miles below the original peaks. Geologists read the layers like a book: the Blue Ridge, the Valley and Ridge province, the Appalachian Plateau - each tells a different chapter of the same long story.

From altitude, the dominant impression is forest - a near-unbroken canopy that turns the ridges the soft, hazy blue that gave the Blue Ridge Mountains their name. The haze is real, made by terpenes the trees release on warm days. The Southern Appalachians shelter one of the most biodiverse temperate forests on Earth, with more tree species in a single Smoky Mountain cove than in all of Europe. Salamanders thrive here in numbers found nowhere else - the southern highlands are sometimes called the salamander capital of the world. Black bears, brook trout, and migrating warblers all depend on this corridor of green.

For European settlers pushing west in the 1700s, the Appalachians were a barrier as much as a landscape. The Cumberland Gap, in present-day Kentucky, became the doorway through which hundreds of thousands of pioneers funneled in the decades after Daniel Boone widened the trail in 1775. The mountains shaped American culture as much as American maps. Isolated hollows preserved old ballads and dialects long after the lowlands forgot them. Coal seams deep beneath the ridges fueled the Industrial Revolution and built fortunes - and left mining communities whose hard history is still being written. The Appalachian Trail, conceived in 1921 by forester Benton MacKaye, knits the whole 2,198-mile spine together as a single footpath.

Compared to the Rockies or the Alps, the Appalachians look gentle - long parallel ridges in the central section, rounded summits in the south. The highest point, Mount Mitchell in North Carolina, reaches 6,684 feet. That's modest by global standards, but the mountains' age gives them a different kind of grandeur. Every river that crosses the ridges in defiance of the topography - the Susquehanna, the Potomac, the New River - has carved its way down as the land rose around it, a process called antecedent drainage. These mountains do not announce themselves. They reveal themselves, slowly, the way old things do.