Double Ditch State Historic Site Magnetic gradiometry can reveal changes in landscapes invisible to the human eye. This image shows Mandan villagers retreating into smaller settlements as they rebuilt their fortified walls between the early 1500s and 1600. Drought, shortages of resources, conflict with rival groups, or disease likely contributed to a decline in population and the gradual retrenchment of the area of settlement.
Courtesy of Professor Kenneth L. Kvamme, University of Arkansas