Just south of Cresco, Iowa (along corridors like US-63 and local Howard County roads), the area sits on Paleozoic sedimentary bedrock belonging to the Devonian Period, heavily influenced by surrounding glacial drift.

Key Stratigraphy & Lithology

1. Cedar Valley Group (Middle to Upper Devonian)

   • Primary Rock Types: Fine- to medium-grained dolomite and fossiliferous limestone.

   • Formations Included: The area is dominated by units of the Cedar Valley Group, notably the Little Cedar, Coralville, and Lithograph City Formations.

   • Visual Characteristics: Outcrops in roadcuts and local quarries range from tan, buff, to brownish-gray weathered dolomite and pale gray limestone beds. Some beds exhibit chert nodules or thin shaly partings.

2. Surficial Cover (Quaternary Glacial Drift)

   • Overlying the bedrock along the road is a layer of Quaternary material characteristic of the Iowan Surface: unsorted pre-Illinoian glacial till (clay, sand, and gravel, including glacial erratics like granite cobbles) topped by a thin mantle of windblown loess.

Geologic Features to Look For

• Karst Features: Because the carbonate rocks (limestone and dolomite) are dissolvable by groundwater, the landscape south of Cresco features shallow bedrock, sinkholes, and solution fractures.

• Paleozoic Fossils: Devonian carbonate exposures in this zone frequently contain marine fossils, including brachiopods, stromatoporoids (laminar and hemispherical fossil sponges), crinoid stem segments, and favositid (honeycomb) or rugose corals.