The Department of the Interior is a decentralized agency with more than 67,000 employees and over 180,000 volunteers in nearly 2,400 locations throughout the United Sates and Puerto Rico. The agency provides access to the natural and cultural heritage of the U.S. It offers recreational opportunities, conducts scientific research, and provides stewardship of energy and mineral resources. The Department of the Interior also conserves and protects fish and wildlife. The agency collects revenues from energy, mineral, grazing, timber, recreation and land sales. It operates National Park Service, Minerals Management service, and the Bureau of Land Management. The Department of the Interior additionally operates the U.S. Geological Survey, which conducts groundwater and surface water studies. The agency administers the Office of Surface Mining's Abandoned Mine Land Program.