The upper Cache River drains a portion of the Shawnee Hills. The area is hilly with many rock outcroppings. The rock is sandstone, deposited about 350 million years ago during the Mississippian period, when shallow seas covered Illinois. The Shawnee Hills are part of the Ozarks. Collision of continental plates uplifted the area, which lies along a plate wrinkle. Much of the hilly topography was carved by erosion and downcutting of rivers and streams. This area was also not flattened by Ice Age glaciers. The ice stopped about 45 kilometers (28 mi.) north of here.
The Cache River Basin is one of the most biologically diverse areas in Illinois. A large number of species are found here because northern, southern, and eastern species all come together here and there are many habitats.
As many as 20 natural community types occur, including limestone and sandstone glades, floodplain, bottomland, and dry upland forests, swamps, and caves. Scientists studying the area have counted 128 species of native breeding birds, 49 species of mammals, 32 amphibians, 43 reptile species, 84 species of fish, 47 native mussel species, and 34 crustaceans.
Learn more about swamps in our Forest Web exhibit.
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