PKAA, Twin Sisters Mine Closure Project

The Twin Sisters Mine Closure Project is located in western Boulder County in the vicinity of Nederland in mountainous terrain at elevation ranging from 7,000 to 9,000 feet. The Twin Sisters Mine Closure Project includes 26 mines and 2 maintenance mines primarily in the area of Magnolia Rd in western Boulder County. The project area was mined by underground mining methods from 1860's until the mid-1960's for tungsten, gold, and silver. As mining ceased, many of the mine openings remaining from the operations were left in an unsafeguarded condition. The mine openings are located on USFS land, Boulder County land, and private claims. Many of these openings are actively collapsing. The area is popular with recreationalists who hike and bike in the area, camping, hunting, and multiple private land owners who live in and use the area. Mine features will be safeguarded using backfilling (20), monolithic plugs (1), corrugated steel pipes with bat ladders (3), vertical bat grates (1), and native rock bulkhead with bat access (1). The two maintenance features will require backfilling.