Clark invented a river—the Multnomah, a supposed tributary of the Columbia—to drain a large area of the intermountain West now known as the Great Basin. The concept of a region like this one, in which the waters flowed inward and simply disappeared, “wasn’t on the radar screens of early-nineteenth-century geographers,” says John Logan Allen of the University of Wyoming. “To imagine a river that started nowhere and went nowhere would have been like imagining water flowing uphill.”