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A shut-in is an Ozark term for a river that is naturally confined within a deep, narrow channel. The river becomes unnavigable even by canoe due to the rapids and narrow channels produced as the stream encounters a more resistant rock that is more difficult to erode. In the Johnson's Shut-Ins State Park in Missouri, hard rhyolite and a diabase dike divert the stream into many small streamlets following a complex joint system, "shutting" the river.
The term has an origin in Appalachia, where it was used to refer to a narrow river gorge confined by resistant rock layers.
Examples can be found in Johnson's Shut-Ins State Park in Missouri, where the Black River has become confined in a shut-in. More than ninety other "shut–ins" occur within and around the St. Francois Mountains region of southeast Missouri.
In southern Illinois, the Burden Falls Wilderness area includes a narrow canyon below a waterfall that is confined by a resistant sandstone layer. The gorge is referred to as a shut–in, following the Appalachian usage for the term.