What you are looking at is the Lockheed Martin Helendale RCS Evaluation Range.
Basically its a very smooth and flat strip of concrete and at the end there is an underground bunker with a pair of doors that open in the ceiling. An
RCS prototype is raised out of the bunker on a pylon and the radar returns are measured.
If you ahng around long enough you might get to see an interesting aircraft shape etc.
INTERESTING FACT: The concrete strip at Helendale is so flat it has actually been corrected to rule out the curvature of the earth.