https://www.auger.org/outreach/cosmic-rays/timeline-cosmic-rays

“The highest-energy cosmic ray ever detected was observed on October 15, 1991 by the Fly’s Eye cosmic ray detector in Utah, USA. The detector is located in the desert in Dugway Proving Grounds 75 miles southwest of Salt Lake City. The Fly’s Eye detects cosmic rays by observing the light that they cause when they strike the atmosphere. When an extremely high-energy cosmic ray enters the atmosphere, it collides with an atomic nucleus and starts a cascade of charged particles that produce light as they zip through the atmosphere. The charged particles of a cosmic ray air shower travel together at very nearly the speed of light, so the Utah detectors see a fluorescent spot move rapidly along a line through the atmosphere. By measuring how much light comes from each stage of the air shower, one can infer not only the energy of the cosmic ray but also whether it was more likely a simple proton or a heavier nucleus. “

History repeats itself.