For most of West Virginia, the rock beneath our feet is sedimentary—layers of sand, mud, and other materials that hardened over time. These sediments were laid down during the Paleozoic Era, between about 570 and 230 million years ago, when much of the area was covered by a shallow sea. Erosion from ancient mountains to the east washed sediments into this sea, where they slowly built up layer after layer over millions of years, forming the foundation of today’s landscape.