About 600 million years ago, a huge landmass called Old Appalachia (pictured in the darkest shade of red) was located where the eastern United States is today. Made of ancient igneous and metamorphic rock, it bordered a shallow inland sea that once stretched toward the Rocky Mountains. Over time, erosion washed sediments into the sea, forming thick layers of rock. Later, powerful mountain-building forces—known as the Appalachian Orogeny—lifted and folded these rocks into mountains. After millions of years of uplift and erosion, the landscape became what we now call the Appalachian Highlands, which include the Piedmont, Blue Ridge, Ridge and Valley, and Plateau regions of West Virginia.