An Impossible Journey

In May 1869, John Wesley Powell, a former Union Army major who had lost most of his right arm in the Battle of Shiloh, led 10 explorers in launching four heavy wooden boats loaded to the gunwales with 10 months of supplies.

Three of the boats were made of oak, more suitable for cruising lakes than busting through rapids. None of the men were experienced boatmen. The one-armed captain of the crew h...