This is Lockheed Martin's radar cross-section (RCS) measurement facility at Helendale, California. Airplanes, components, and scale models are raised
up on pylons and turned at various angles to the radar.
Test articles are prepared inside the building and then moved out and mounted on the large pylon. There is a substantial amount of subterranean
infrastructure to raise and lower the pylon on a hydraulic jack. I have seen some blueprints. It's pretty impressive.
The most recent testing I have seen at the site involved signature measurements for the X-35/F-35A Joint Strike Fighter.