Christmas Valley Radar Station, Oregon

Shortwave bands have been used for over the horizon radar, to detect things like rockets and aircraft. Though most of these land-based systems were terminated in the 1990s or before, their footprint and some outbuildings remain. One type of system, known as OTH-B (Over-the-Horizon-Backscatter) included facilities on the east coast and the west coast. It was developed for the Air Force by General Electric Aerospace in the 1980s, and went operational in 1990. It involved a transmitter site, with a large antenna array, and a receiving location, with another antenna array, some miles away. The west coast transmitting site operated at the Christmas Valley Air Force Station in Oregon. The receiving station was at the Tule Lake Air Force Station in California. Built as an early-warning system for military defense, the signal was also used by the Border Patrol to track airplanes, and NOAA to track tides and currents. The operation closed in 1997, and the transmitting site was deactivated in 2002. The antenna arrays and transmitters were removed in 2007, though some buildings and towers remain.