A couple of people have asked, in comments and in emails, what are ’shut-ins’, such as the ones featured in Pink Saphires and Blue Diamonds.
According to the Missouri Conservationist:
Shut-ins are geologic features that are formed as streams erode away relatively soft limestone and dolomite, until they encounter deeper igneous rock, which is much harder to erode.
Streams and rivers running through igneous rock can cut only deep, narrow channels and are given little opportunity to form meanders as most streams do. As a given volume of water passes though these shut-ins, the water’s velocity increases, creating the rushing, bubbling effect that makes the scene at Amidon so appealing.
The only reference to shut-ins I could find are to those in Missouri, leading me to believe these may be a purely Missouri phenomena.
I have been to, and photographed both the Johnson Shut-Ins and the recently described Castor. Both are wonderful places, but the Castor is the one that’s stolen my heart.