From 1958 through 1980, this incongruous four story (82 foot) monolith was the centerpiece of the "Almaden Air Force Station", a long-range radar site that was part of NORAD's SAGE early warning system. The blast-hardened concrete building served as the platform for an FPS-24 radar system, a massive 120 foot wide reflector that emitted a 5 megawatt VHF pulse, continuously rotating at 5 RPM.
Notoriously, the signal disrupted TV and radio reception throughout the San Jose area.