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