The forgotten natural prairie mounds of the Upper Midwest: Their abundance, distribution, origin, and archaeological implications

Mima mounds in North America are primarily known from the western states of Washington, Oregon, and California; the Rocky Mountains; the mid-lower Mississippi Basin; and Louisiana-Texas Gulf Coast. By contrast, their former extent and abundance across the Upper Midwest prairie belt has never been systematically established due to their destruction by agriculture and historic confusion as to whether they were natural or anthropic mounds. Recent maps showing their distribution identify only two small moundfields, one centered on Waubun Prairie in western Minnesota, the other on Kalsow Prairie in north-central Iowa. But in fact, natural mounds were once a common feature of many Upper Midwest prairies, having extended from Kansas, Missouri, and Illinois north into Wisconsin, Iowa, Minnesota, the Dakotas, and across the prairies and parklands of Canada. Several remnant tracts, intact and preserved, bear witness to their former much greater extent. This chapter documents the original distribution across the prairie belt, which has implications for their origin insofar as it falls more or less entirely within the range of the Geomyidae (pocket gopher) family of fossorial rodents. Natural prairie mounds in the Upper Midwest invariably are found where limitations to vertical burrowing occur, or did occur, which leaves lateral burrowing as the only option to these and other soil animals. Owing to extensive overlaps between natural mounds and morphologically similar prehistoric “Moundbuilder” mounds, the idea is advanced that prairie mounds were opportunistically used for prehistoric interments, and later as ideation templates for prehistoric burial, effigy, and other mounds and utilitarian structures.