Natural Stone Bridge and Caves in Pottersville, New York, is a notable eastern Adirondack site where Trout Brook has carved an unusual system of eleven marble caves, waterfalls, potholes, and short underground passages. Its best-known feature, Stone Bridge Cave, has the largest marble cave entrance in the eastern United States. The marble dates to about 1.1 billion years ago, but the caves are only about 14,000 years old, formed after the last glacial period redirected the brook into soluble rock. Known since the mid-18th century, the site became a tourist attraction in 1929 and remains valued for its rare geology and still-active cave formation.