Strange objects throughout the United States

As you can see from these pictures, most of the United States is dotted with such strange objects. Do you think that what they have been used previously? Answer below.





This site, which were used for calibration, testing cameras installed on board the reconnaissance aircraft.
Nowadays, they are no longer used, all of them were made in the 1950s and 1960s, their form, location and size of the standardized US Air Force and NASA.