The type of rock that primarily makes up the Appalachian Mountains is Sedimentary rock.

The Appalachian Mountains are predominantly composed of sedimentary rocks, including sandstone, shale, and limestone. These rocks were formed from ancient ocean deposits, river sediments, and other geological processes over millions of years. While there are also significant formations of metamorphic rock and some granite in certain areas, sedimentary rock is the most prevalent type found throughout the mountain range. The layered appearance of these rocks contributes to the unique geology and landscape of the Appalachians.