A shut-in is a type of rock formation found in Ozarks streams where they  carve through a mountain range , causing a complex of pools, rivulets, rapids and plunge pools.  Shut-ins are inherently confined to a narrow valley or canyon, with the river valley widening out both above and below the formation. Because the rock resists downcutting, streams typically descend at relatively steep gradient through shut-ins, with the downstream terminus of the formation often marked by a very large plunge pool. The river becomes unnavigable at shut-ins even by canoe due to the rapids and narrow channels.   Johnson's Shut-Ins State Park in Missouri, with its hard rhyolite and a diabase dike that divert the Black River into many small streamlets following a complex joint system, is the most well known example.Beveridge, p.39 - 62 More than ninety other shut–ins occur within and around the St. Francois Mountains region of southeast Missouri. The term has an origin in Appalachia, where it was used to refer to a narrow river gorge confined by resistant rock layers. 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. References Beveridge, T. R., Geologic Wonders and Curiosities of Missouri, Missouri Department of Natural Resources, 2nd ed. 1990, p. 39–62
A shut-in is a type of rock formation found in streams in the Ozarks, comprising pools, rivulets, rapids and plunge pools. The term has an origin in Appalachia. Description A shut-in is a rock formation that carve through a mountain ranges , causing a complex of pools, rivulets, rapids and plunge pools. They are found in streams in the Ozarks. Shut-ins are inherently confined to a narrow valley or canyon, with the river valley widening out both above and below the formation. Because the rock resists downcutting, streams typically descend at relatively steep gradient through shut-ins, with the downstream terminus of the formation often marked by a very large plunge pool. The river becomes unnavigable at shut-ins even by canoe due to the rapids and narrow channels. Etymology The term has an origin in Appalachia, where it was used to refer to a narrow river gorge confined by resistant rock layers. Examples Johnson's Shut-Ins State Park in Missouri, with its hard rhyolite and a diabase dike that divert the Black River into many small streamlets following a complex joint system, is the most well known example.Beveridge, T. R., Geologic Wonders and Curiosities of Missouri, Missouri Department of Natural Resources, 2nd ed. 1990, p. 39– 62 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. References 
R
Ozarks streams where they
streams in the Ozarks, comprising pools, rivulets, rapids and plunge pools. The term has an origin in Appalachia.
A
Description A shut-in is a rock formation that
R
range
ranges
A
They are found in streams in the Ozarks.
A
Etymology The term has an origin in Appalachia, where it was used to refer to a narrow river gorge confined by resistant rock layers.
A
Examples
R
p.39 -
T. R., Geologic Wonders and Curiosities of Missouri, Missouri Department of Natural Resources, 2nd ed. 1990, p. 39–
D
The term has an origin in Appalachia, where it was used to refer to a narrow river gorge confined by resistant rock layers.
R
. The
; the
D
Beveridge, T. R., Geologic Wonders and Curiosities of Missouri, Missouri Department of Natural Resources, 2nd ed. 1990, p. 39–62