NOGALES, ARIZONA—Live Science reports that independent scholar Deni Seymour unearthed a 40-pound bronze cannon—reported to be the oldest known firearm in the continental United States—at the site of San Geronimo III, or Suya. The short-lived settlement was founded in the Santa Cruz Valley by members of the expedition led by Spanish conquistador Francisco Vázquez de Coronado. Inspired by reports of golden cities, Coronado set out northward from Compostela on February 23, 1540, with more than 300 European men and perhaps more than 2,800 people in total. Separate parties that were sent in different directions explored what are now the states of Arizona, New Mexico, Texas, and Kansas. Shortly after the establishment of San…..