On May 24, 1869 a one-armed Civil War veteran named John Wesley Powell and a ragtag band of nine mountain men embarked on the last great quest in the American West. No one had ever explored the fabled Grand Canyon, to adventurers of that era a region almost as mysterious as Atlantis -- and as perilous. The ten men set out down the mighty Colorado River in wooden rowboats. Six survived. Drawing on rarely examined diaries and journals. Down the Great Unknown is the first book to tell the full, true story.