Mississippi River Overlook

The valley of the Mississippi River is one of the most distinctive landscape features of the central United States. Set in a geologic framework of ancient sea floors and glacial flood waters, this rock-lined corridor hosts interesting communities of plants and animals. For centuries the valley has lured prehistoric and historic populations to its scenic flowing contours of waterways, islands and bluffs. Here in northeastern Iowa, the Mississippi has carved a deep, steep-sided valley into sedimentary bedrock. Between 35 and 10 thousand years ago, this river valley served as a major channel for enormous volumes of glacial meltwater and outwash sand and gravel released from melting continental glaciers to the north and west of this region. The level valley floor, occupied by the town of Guttenberg and Lock and Dam No. 10, is underlain by over 150 feet of these meltwater-transported sediments, indicating deep scouring of the bedrock floor and then partial filling of the river valley.

The high bluff here on the west valley wall exposes the internal composition of the landscape into which the Mississippi entrenched its valley. These layered limestone strata are formed of much older deposits of lime-rich muds that accumulated in the shallow, tropical seas that covered this area during Ordovician time, approximately 440 million years ago.

(Continued on other side)