Shut-in (river)

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.

The term has an origin in Appalachia, where it was used to refer to a narrow river gorge confined by resistant rock layers.

[1] 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.

[1] 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.