IN THE WINTER OF 1846, two years after the murder of founding prophet Joseph Smith, some 3,500 Mormons paused at the outset of the grueling westward exodus that would eventually lead them to Salt Lake. Under the leadership of Brigham Young, they gathered across the Missouri River from Iowa in what would be Nebraska but was then Omaha Indian territory. The environmental historian Jared Farmer sets the scene: “Young needed a wintering place to prepare for the migration. He could have set up camp in Western Iowa, but the Mormon persecution complex propelled him across the Missouri River to unorganized territory. Better to live among the red men than among whites. Young knowingly violated a federal law that forbade contact with Indians on reserved land. He went ahead and negotiated his own extralegal treaties with Omahas and Otoes, both of whom claimed the land at Winter Quarters.”...