A shut-in is an Ozark term for a river that's naturally confined within a deep, narrow channel. The river becomes unnavigable even by canoe due to a 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

Johnson's Shut-Ins State Park

Johnson's Shut-Ins State Park is a Missouri state park on the East Fork Black River consisting of in Reynolds County. The park is jointly administered with adjoining Taum Sauk Mountain State Park, and together the two parks cover in the St...

 in Missouri hard rhyolite

Rhyolite

This page is about a volcanic rock. For the ghost town see Rhyolite, Nevada, and for the satellite system, see Rhyolite/Aquacade.Rhyolite is an igneous, volcanic rock, of felsic composition . It may have any texture from glassy to aphanitic to porphyritic...

 and a diabase

Diabase

Diabase or dolerite is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. In North American usage, the term diabase refers to the fresh rock, whilst elsewhere the term dolerite is used for the fresh rock and diabase refers to altered material...

 dike

Dike (geology)

A dike or dyke in geology is a type of sheet intrusion referring to any geologic body that cuts discordantly across* planar wall rock structures, such as bedding or foliation...

 diverts the stream into many little streamlets following a complex joint system "shutting" the river.

The term had an origin in Appalachia

Appalachia

Appalachia is a term used to describe a cultural region in the eastern United States that stretches from the Southern Tier of New York state to northern Alabama, Mississippi, and Georgia. While the Appalachian Mountains stretch from Belle Isle in Canada to Cheaha Mountain in the U.S...

 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

Black River (Arkansas)

The Black River is a tributary of the White River, about 300 mi long , in southeastern Missouri and northeastern Arkansas in the United States. Via the White River, it is part of the Mississippi River watershed...

 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

Burden Falls Wilderness

The Burden Falls Wilderness is a 3,775-acre unit of the Shawnee National Forest. It is located in northwestern Pope County and southwestern Saline County, Illinois. The wilderness is characterized by roadless second-growth hardwood forest, punctuated by a small, seasonal waterfall on Burden Creek...

 area includes a narrow canyon below a waterfall that is confined by a resistant sandstone

Sandstone

Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...

layer. The gorge is referred to as a shut–in following the Appalachian usage for the term.