The park is home to many interesting geologic formations such as the chevron folds visible in both Maryland and LoudounHeights and the old phyllite quarry sites located within the historic town itself. A favorite among visitors are the Stone Steps leading up to Jefferson Rock, which were carved directly into the phyllite in the lower town in the 19th century. Another notable geologic formation is the water gap between Maryland and LoudounHeights. This gap was formed about 360 million years ago when the Potomac River began cutting through the Appalachian Mountains. Today this gap marks the confluence of the Potomac and ShenandoahRivers and is considered by many to be the area's most prominent geological feature.