The Durango & Silverton Narrow Gauge Railroad (D&SNG) is a 3 ft (914 mm) narrow gauge heritage railroad that operates 45.2 miles (72.7 km) of track between Durango and Silverton, in the U.S. state of Colorado. The railway is a federally designated National Historic Landmark and is also designated by the American Society of Civil Engineers as a Historic Civil Engineering Landmark.