Mississippi River Overlook
(Continued from other side)

This particular bluff, from here to the bottom of the hill, contains the most complete exposure of the Galena Group rocks known. This widespread rock sequence is named for outcrops at Galena, Illinois, and the term “galena” refers to the lead ore which has been mined from this district for at least the last 300 years.

These carbonate rocks are also characterized by numerous vertical and horizontal fractures and crevices. Through geologic time some of these openings were slowly enlarged by seeping groundwater. The result is the development of sinkholes at the land surface, underground caverns, and springs along steep valley sides throughout this region. The flow of moist cool air down through these subterranean passageways and out over the valley slopes provides isolated, rare habitats for unusual assemblages of plants normally found in more northern climates.

In addition to the valley’s offerings in earth history and ecological adaptations, this natural corridor was an important route of both prehistoric and historic exploration, trade, settlement, and transportation.