Strange colossal shapes dot the Sonoran Desert in Arizona, x-shaped relics of a once top-secret Cold War spying project. Known as the Corona program, the surveillance initiative by the CIA and US Air Force involved using satellites to take aerial photographs of the Soviet Union and the People’s Republic of China. The cameras on these satellites were calibrated with concrete crosses 60 feet in diameter. Their exposed 70mm film was later jettisoned in space, the parachuting capsules caught in mid-air by plane. The calibration markers helped assure that the film was in focus, and that there was a landscape measure to accurately assess the size of pictured objects.

Approximately 256 of these markers were placed on a 16-square-mile grid in Arizona, spaced a mile apart. Long after Corona’s end and its declassification in 1995, around 100 remain. Phoenix-based artists Julie Anand and Damon Sauer have spent three years tracking them down for a project called Ground Truth: Corona Landmarks. ... The Corona program produced what are recognized asthe first maps of the Earth from space. Anand and Sauer photograph the markers with a heavy emphasis on the sky, to which they later add the paths of satellites that were passing by at the exact time of the picture. On their project site, you can zoom in on high-resolution photographs to see the names of the satellites, which are numerous, visualizing how ubiquitous they’ve become since the Corona program.