Please don't touch or climb on the cliff, as it is fragile and could easily be damaged! Thank you!
Where you now stand, Ice Age glaciers last stood about 200,000 years ago (though the last Ice Age ended a mere 10,000 years back). Glaciers would have erased small streams like Hall Creek, and maybe bigger ones such as the Rock River. Even mighty waters like the Mississippi were pushed aside by the glacier's advance. After the climate warmed and the ice melted, new streams formed. In some places, these new creeks dug out and re-occupied old valleys that had been filled by glacial deposits, while other streams had to begin eroding new valleys through solid bedrock. Hall Creek eroded into dolostone on the east side of its valley (in front of you) to form the Dells. Even though the rock looks solid, it is fairly porous and had many horizontal cracks, such as the fairly large one you can see about halfway up the cliff wall. Groundwater comes to the surface at these cliffs, providing a cool, moist, and definitely fragile habitat for lichens, mosses, and liverworts, as well as for snails, insects, and spiders. Note that this plant community is literally hanging onto bare rock! Please resist the temptation to climb the Dells or take rock or plant souvenirs. These actions would cause permanent damage. This is a delicate and rare place — the showpiece of our Forest Preserve — so please just stand back and enjoy!