Now retired, Daniel Lenihan was the founding chief of the National Park Service’s Submerged Cultural Resources Unit (now the Submerged Resources Center). He has been a frequent contributor to Natural History. His previous stories include “The Arizona Revisited” (November 1991), “Raptures of the Deep” (November 1996), and, most recently, “Diving Montezuma Well” (May 2011). Lenihan has also written several books, including Submerged: Adventures of America’s Most Elite Underwater Archeology Team (Newmarket Press, 2002) and, with Gene Hackman, Escape from Andersonville: A Novel of the Civil War (St. Martin’s Press, 2008).