Mexican settlers first came to the valley of the Rio Grande to establish their ranchos in the 1750s. Two centuries later the Great River, dammed in an international effort by the U.S. and Mexican governments to provide flood control and a more dependable water supply, inundated twelve settlements that had been built there. Under the waters of the new Falcon Reservoir lay homes, businesses, churches, and cemeteries abandoned by residents on both sides of the river when the floods of 1953 filled the 115,000-acre area two years ahead of schedule.

The Smithsonian Institution, the National...