Geologic Overview of the Paleozoic Plateau Region of Northeastern Iowa

Steep slopes, varied slope aspects, and entrenched stream valleys carved into Paleozoic-age rocks provide the geologic framework for the unique and diverse ecology of northeastern Iowa. Differential weathering and erosion of these variable rock types resulted in irregular surface slopes in a multi-stepped, high-relief landscape. Additionally, solution of carbonate bedrock produced karst topography, cavern systems, ice caves, cold-air drainage, and perennial groundwater springs. The so-called Driftless Area in Iowa was glaciated repeatedly in Pre-Illinoian time, and should not be called Driftless. The name Paleozoic Plateau for this physiographic region more accurately describes some of its special aspects and also incorporates the much larger region of distinctive physiography and ecology referred to by biologists. Although the bedrock geology provides the framework for this unique region, the high relief is a product of more recent geologic history. Evidence from studies of the upland Quaternary stratigraphy and erosional history, the development of the karst system, and the fluvial deposits in the stream valleys reveal a complex Pleistocene history. Stream erosion since the last episode of glaciation (ca. 500,000 years before present) produced the deeply dissected landscape. Current research suggests that the major episode of deep-valley incision occurred during the Wisconsinan. Numerous late-Wisconsinan terraces stand 12-25 m above the present streams. A large portion of northeastern Iowa\u27s rugged terrain is remarkably young