The Silver Thread Scenic and Historic Byway is a 117-mile (188 km) National Scenic Byway, National Forest Scenic Byway, and Colorado Scenic and Historic Byway located in Gunnison, Hinsdale, Mineral, and Rio Grande counties, Colorado, USA. The byway explores the historic silver mining region in the high San Juan Mountains of southwestern Colorado. The byway follows Colorado State Highway 149 for its entire length from U.S. Highway 160 in South Fork to U.S. Highway 50 west of Gunnison. The byway crosses the Continental Divide at Spring Creek Pass, elevation 10,898 feet (3,322 m), and crests at Slumgullion Summit, elevation 11,530 feet (3,514 m). Lake San Cristobal is formed by the Slumgullion Earthflow, a National Natural Landmark.