The Mitchell Plain is a karst

KARST

Kilometer-square Area Radio Synthesis Telescope is a Chinese telescope project to which FAST is a forerunner. KARST is a set of large spherical reflectors on karst landforms, which are bowlshaped limestone sinkholes named after the Kras region in Slovenia and Northern Italy. It will consist of...

 area of relatively low relief. The extensive underlying cave system developed in Mississippian age limestone

Limestone

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

 bedrock. Surface drainage is rare due to most streams in the area disappearing into caves or joints within the rock.

The limestone is a vestige of an early shallow craton

Craton

A craton is an old and stable part of the continental lithosphere. Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates. They are characteristically composed of ancient crystalline basement rock, which may be covered by...

ic sea that covered what would become Indiana

Indiana

Indiana is a US state, admitted to the United States as the 19th on December 11, 1816. It is located in the Midwestern United States and Great Lakes Region. With 6,483,802 residents, the state is ranked 15th in population and 16th in population density. Indiana is ranked 38th in land area and is...

, while the North-South linearity of the region is left over from the Cincinnati Uplift

Cincinnati Arch

The Cincinnati Arch is a broad structural uplift between the Illinois Basin to the west, the Michigan Basin to the northwest and the Appalachian Basin and Black Warrior Basin to the east and southeast. It existed as a positive topographic area during Late Ordovician through the Devonian Period...

, sloping the rock layers from a high in the East sloping downward towards Cairo, Illinois

Cairo, Illinois

Cairo is the southernmost city in the U.S. state of Illinois. It is the county seat of Alexander County. Cairo is located at the confluence of the Mississippi and Ohio rivers. The rivers converge at Fort Defiance State Park, an American Civil War fort that was commanded by General Ulysses S. Grant...

.

The Mitchell Plain is bound by the older Norman Upland on the East and the younger Crawford Upland on the West.