Geology
The Osage Plains is underlain by soft shales with interbedded sandstones and limestones of late Mississippian to Pennsylvanian age. Some of the rocks prevalent in the Osage Plains are Mississippian limestone, limestone shale, Ordovician dolomite, and coal. There are also clay and shale within the Pennsylvanian bedrock.
The area contained two major mining areas. The biggest was the Tri-State Lead and Zinc Region, consisting of nearly 2,000 sq mi (5,200 km2). This was the largest concentration of zinc deposits anywhere in the world. Most mining sites have closed, mainly due to health and other environmental issues, but more than $1 billion worth of lead and zinc were extracted from the area during the active mining days. The other major mining was for bituminous coal. But due to air quality standards, this region's coal is in low demand due to its high sulfur content.
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