Effigy Mounds Administrative History

Along the Mississippi River in southeastern Minnesota, northeastern Iowa, in Wisconsin and northern Illinois lies a region commonly known as the "Driftless Area," so called because it escaped the great ice blankets of the Pleistocene glaciations. [1] Although the Driftless Area extends well into Wisconsin, in Iowa its eastern limit is clearly marked by the three- to seven-mile-wide Mississippi trench.

Because the terrain in this region was not first planed by the advancing glaciers then filled with glacial till as the ice sheets retreated, the topography differs markedly from that of the surrounding areas. Instead of low, gently rolling hills woven together with well—integrated systems of streams, the Paleozoic plateau is characterized by deep—cut meandering stream beds and very steep slopes. Over time, the Mississippi created random terraces along its banks; the terraces provide small relief from the abrupt bluffs which dominate the shores. Punctuating the shoreline are bluffs where sandstone and limestone bedrock strata, elsewhere covered by the glacial till, have been exposed by the erosion of the streams. Elevations often measure up to 500 feet. Ridge tops are often covered with loess deposits. [2] For centuries, a scattering of earthen bears and birds have nestled amidst mounds of less spectacular shapes along the banks and upon the ridge tops in the area which became Effigy Mounds National Monument.

Like the rest of eastern Iowa, the Paleozoic plateau is an environmental mosaic, with fingers of the eastern wood lands extending westward and those of the grassland steppe continuing—to the east. Its freedom from ice cover during the last glaciation left the area botanically unique. It is the only place in the state of Iowa where stands of northern deciduous forest, more commonly found at or near the Canadian border, exist. The deep ravines and precipitous bluffs furnish micro—environments for entirely different plants. On the northern slopes are niches supporting plant communities that normally flourish much nearer the Arctic, while some south-facing slopes provide habitats for the growth of species usually found in drier regions. [3]

There is some evidence that the open prairie expanses in the Driftless Area are much smaller now than they were before the arrival of Europeans. This may be due in part to the cultivation and then abandonment of some fields, and in small part to lumbering activities in the past. The greatest probable cause of the forest spread, however, seems to be the absence of fire. There are indications that prairie fires, either naturally occurring or started by the prehistoric inhabitants for their own purposes, swept through the area at fairly frequent intervals. Not serious enough to harm mature trees, these fires were sufficient to maintain the prairie openings by destroying seedling trees and encroaching brush. The rigid control of fire during the last several decades has upset the balance, allowing the forested areas to expand at the expense of the prairies. [4]