The main impact area constitutes the inner ring. Bouguer gravity anomaly maps show that this feature includes a small uplift that is centrally located. Exploratory core drilling around the structure has not penetrated deeper than 100 m, but from available data the main impact area is full of breccias that include six facies: crystalline basement breccia (only found in the eastern side), dilation breccia, megabreccia, injection breccia, fracture breccia, and resurge breccia. Post-impact middle Mississippian carbonates buried part of the structure. These strata were exposed subaerially and mostly removed below the sub-Pennsylvanian unconformity. Early to middle Pennsylvanian clastics re-buried the structure and partly have been exhumed by subsequent gentle uplift and erosion during the Ouachita orogeny. This mid-Mississippian impact is remarkably well preserved.
The distribution of strain in the outer ring is related both to the heterogenous material strengths of the target rocks and to the trajectory of the impactor. Proximal to the impact in the northeast, chaotic blocks of Mississippian rocks show brittle brecciation over ductily folded and faulted blocks associated with material flow. Injection breccias fill interstitial areas between megabreccia blocks. Resurge breccia caps this succession. To the northwest, thick to massive beds of brittle carbonates in the lower Burlington-Keokuk limestones (undivided) generally behaved as thin thrust sheets where siltstone of the lower Mississippian (Kinderhookian) Northview Formation served as a décollement. Thrust faulting also is exposed distally to the north and northeast at road cuts near Brush Creek and Weaubleau Creek on Highway 82. Resurge breccia is gradational with the sediments of the upper Burlington-Keokuk limestones in the northeasternmost exposures beyond the tectonic rim.
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