Castor River Shut-ins Natural Area, MO

After our venture to a creek bed with no creek, Rob and I decided to venture to other areas with creeks/ streams/ rivers and see if the drought had effected them in the same dramatic manner. We chose the Castor River Shut-ins Natural Area (N37° 34.128’ W90° 09.299’). Shut-ins? We didn’t know either, having never heard this term as applied to a natural history description. We learned that shut-ins refers to a place where the river’s breadth is limited by hard rock (igneous in origin) that is resistant to erosion. The river then erodes through the hard rock in multiple small areas instead of one large waterfall.  The Castor River Shut-ins are the only known pink granite shut-ins in Missouri.

Natural history note: In this area of the Breadtray formation in southern Missouri, most of the exposed igneous rocks of the St. Francois Mountains are rhyolite rather than granite. Both granite and rhyolite are formed from magma, the difference being that granite is cooler underground and later exposed and rhyolite is magma that cools above ground.

Our venture to the Castor River Shut-ins was successful in that there was actually water flowing in the Castor River so we could experience the nature of the Shut-ins rather than just see some eroded rock.

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