Silurian strata are exposed at numerous localities ineast-central and northeast Iowa (Fig. 1), where the total Siluriansequence approaches 500 ft (150 m) in thickness. The bulk of thesequence is dominated by dolomite and cherty dolomite characteristically lacking a notable siliciclastic component. The Siluriancarbonates are pervasively dolomitized, except along portions of the northern and northwestern margins of the outcrop belt, where limestones occur. The Silurian early Llandoverian-Ludlovian)dolomite sequence is divided into six formations (Bunker and others, 1985), and a variety of fossil associations characterize the Silurian sequence (Witzke, 1983).
The youngest Silurian rocks in Iowa are exposed in the southern region of the outcrop belt (Fig. 1) and are assigned, in ascending order, to the Scotch Grove and Gower formations. Strata encompassing a part of the Scotch Grove-Gower intervalare well exposed and publicly accessible in the valley of the Cedar River in and around the area of Palisades-Kepler State Park (Fig. 1, about 10 mi (16 km) southeast of downtown Cedar Rapidsand 4 mi (6.5 km) west of Mt. Vernon. The Cedar River has cutthrough Silurian carbonate mound and intermound facies in the area, displaying a series of exposures along forested slopes andbold cliffs, in part overhanging, that form the scenic palisades. The cliffs reach heights to 65 ft (20 m) in places. Hiking trails in the state park provide access to many of the exposures. The most spectacular and instructive exposures encompass localities Athrough F Fig. 1.