In this video you can see a little bit of cold war history in the Arizona desert. These cement X markers were installed by the Army Corps of Engineers in the 60's for US satellites to calibrate distance in photos taken from space over Russian land. Installed precisely 1 mile apart, these X markers, visible from space, help measure Russian inventory, increasing our accuracy to assess what the USSR capabilities were capable of.

You can find these sites yourself using Google satellite view and searching on the coordinates below (remove "Site #").

Corona Satellite Calibration Marker Locations in this video:

Site 1 32.821092, 111.671405
Site 2 32.821000, 111.688802
Site 3 32.820886, 111.738781
Site 4 32.806883, 111.739583
Site 5 32.820855, 111.757708
Site 6 32.806843, 111.757519