Survivorship of Earthworks Mapped by T. H. Lewis in Iowa 1884–1894

Between 1884 and 1894, Theodore Hayes Lewis mapped 370 prehistoric American Indian mounds and earthworks in Iowa as part of a larger survey of mounds in the upper Midwest. Georeferencing remapped Lewis survey notes allows their comparison with modern GIS data including lidar topographic maps, aerial photos, and land records. Of the 370 mounds, 190 (51.4%) are clearly visible in lidar, 160 (43.2%) are probably destroyed, and 20 (5.4%) are undetermined. Data analyses explore the factors that influenced mound survivorship. By far the strongest correlations for survivorship are modern land use, modern ownership, and local landform, with mounds most likely to survive in wooded areas, on public land, and on islands. Iowa data are compared with Lewis map data from Minnesota, revealing Iowa has a far higher survivorship, 51.4% versus 25.6%, likely attributable to land use in the late nineteenth century. Further comparison with Minnesota data suggests perhaps twice as many mounds stood in modern agricultural fields of Iowa before Lewis made his surveys.