The midwestern US is famously flat, but looking at the surface is like reading the last page of a story. The surface is only an apparent denouement of the region’s biography; dirt shoveled onto a shallow grave by the Ice Ages. But humanity has arrived in the middle of the story to a region that is dormant, but still living and breathing, preparing itself to come roaring back like a vengeful spirit. Instead of studying the grave, let’s study what’s in the coffin: the Illinois Basin
Over the past few months we’ve looked at igneous rocks and used some small outcrops to infer their relationships to one another. But to get a full understanding of those relationships, we need a good exposure that lays everything out for us to see. Fortunately for us geologists, the rocks exposed at Tiemann Shut-Ins do exactly that.
At our last stop, we saw the incessant work of water as it slowly etches down into hard Precambrian volcanics. But at Johnson’s Shut-Ins State Park, we can also see the kind of catastrophic damage that a single large flood is capable of.
Johnson’s Shut-Ins State Park is one of the most popular parks in the entire Missouri state park system. The crisp, clear water of the Black River flows through the park, running over rocks in a spectacular series of narrow rapids and wide, shallow pools. But the tranquil setting has been shaped and sculpted by some of the most powerful forces of nature.
Hawn State Park hosts some of the finest hiking trails in the Missouri state park system. Today we’ll go for a hike along Pickle Creek, which has carved a deep ravine and exposed some very interesting outcrops of granite.
Over our last few stops, we’ve gotten a look that the rocks that broadly represent the different levels of the St. Francois volcanic systems. Now we’re going to check out variations on that theme that refine the rough picture of what was going on. Today’s stop will be at Hughes Mountain, an underrated geologic treasure of southeastern Missouri.
So far in our digital trip through the St. Francois Mountains, we’ve looked at the Grassy Mountain Ignimbrite and the caldera responsible for its formation, as well as some igneous activity that postdated its formation. But what was going on deeper in the Earth? To find out, we’re stopping at one of the most gorgeous state parks in the entire midwest: Elephant Rocks State Park.