Mount Graham International Observatory in the Pinaleño Mountains of southeastern Arizona is a University of Arizona astronomy facility developed beginning in 1989 to serve multiple scientific organizations. Its first two telescopes began operating in 1993, and the Large Binocular Telescope later became one of the world’s largest and most powerful optical telescopes, starting independent mirror operations in 2004 and combined operations in 2008. The site supports the Vatican Observatory, the Arizona Radio Observatory, and the Large Binocular Telescope Corporation. It is also significant for long-running conflict over environmental concerns for the Mount Graham red squirrel and Indigenous opposition because the mountain is sacred to and ancestrally used by Western Apache peoples.