The Catoctin Mountains are about 500 million years old and were once similar in size and shape to the Himalayas, with treeless jagged peaks up to 25,000 feet high. They were originally shaped by continents colliding and volcanic activity, then eroded over millions of years to their current size and shape. Because the existing metamorphic rock is harder and less prone to erosion, the mountains remain taller than the surrounding area. Quirauk Mountain is the highest local peak at 2,145 feet, and commonly found rocks include metabasalt, quartzite, limestone, and metarhyolite.