Fibre optic cable marker. The warnings on the marker state that cable locating services must be used before digging in the area. This marker is in the Rocky Flats National Wildlife Refuge in Colorado, USA. This area was formerly the site of a nuclear weapons factory. It was extensively polluted with plutonium. Following a clean-up operation, the US Fish and Wildlife Service opened much of the site to visitors in late 2018. The central area, where nuclear weapons-related production occurred, remains closed. Photographed on 26 December 2018.