Kristen Ohls, Illinois State University


Starved Rock and Matthiessen State Parks in La Salle County, Illinois contain interesting canyons. They were created when glaciers formed and retreated after the last glaciation period, causing stream channels that eroded away much of the sandstone to create the canyons we know and see today. The sandstone member that makes up most of the state parks is known as the St. Peter sandstone, which is very weakly cemented and friable. Landslides are not a frequent occurrence, but happen periodically, sometimes after freeze-thaw events. This is believed to be due to the stability and steepness of the canyon walls and may be created by case-hardening of the rock surfaces due to filling bedrock pore spaces with cement. In this area, the strengthened rock surfaces could also be due to lichen and algae growth, known as lithobionts, on the surface. This sandstone also typically does not react with HCl, but it has been known observed in isolated locations. I hypothesize that this may be due to case hardening or lithobiont occurrences. My research study will investigate these bedrock features and their influence on the geomorphology of the watersheds in Matthiessen and Starved Rock State Parks. My goal is to study why there is variability of bedrock surface characteristics across the canyons in the same sandstone formation. I hypothesize that the reactions to HCl on the rock of the rock were are caused either by surface runoff or case hardening. I will test my hypothesis by observing areas every 5-10 feet at eye level, roughly 5 feet above the ground surface, and mapping which areas reacted to HCl and what biologic or water flow processes could cause the reaction. I will note proximities to the streams, and the rim of the canyon, to see if water flow containing calcite or iron drained down the canyon walls. Observations are likely to indicate different levels of erosion and stability along the canyon walls.