Geological age ~1.47 billion years ago (bedrock).
Epoch Proterozoic eon; Rhyacian period; St. Francois Mountains rhyolite and granite among the oldest exposed rock in Missouri; river incision Quaternary.
Native lands Osage Nation (Wazhazhe) · earlier Paleo-Indian peoples; Osage hunted throughout the St. Francois Mountains; ceded territory via 1808 treaty under duress.
Displacement & Tenure Cession 67: Treaty with the Osage (1808); on December 14, 2005, the Taum Sauk upper reservoir owned by AmerenUE failed, releasing approximately 1.4 billion gallons of water that destroyed the lower park; AmerenUE pled no contest to a federal Clean Water Act violation; a 2009 settlement awarded $102.3 million for park restoration, completed in 2010.
Shadow History The park was assembled over 17 years by Joseph Desloge, heir to a St. Louis lead-mining family whose wealth derived from mineral extraction in the same regional belt as the park's Precambrian geology, and donated to the state in 1955; a 2006 to 2007 USGS study following the 2005 reservoir breach documented elevated turbidity, dissolved aluminum, dissolved iron, and a blue-green surface coloration in the East Fork Black River attributed to rock flour and an alum-based flocculant used by AmerenUE; the East Fork Black River corridor has documented Paleo-Indian occupation extending to approximately 12,000 years BP, and whether the flood disturbed intact subsurface deposits has not been publicly assessed.
Ecology Ozark Highland; dolomite glades; dry chert woodland; rare endemic species in igneous glade communities.
Hydrology East Fork Black River; Taum Sauk Reservoir (upstream); shut-in pools and cascades; 2005 reservoir breach reshaped lower park terrain.
Acreage 8,916 acres
GPS 37.5530° N, 90.8480° W
Johnson's Shut-Ins State Park I · 2026-01-06
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Public Lands Institute — ongoing project
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