Before the invention of electric refrigerators, blocks of ice in insulated wooden cabinets called “iceboxes” kept food from spoiling quickly in warm climates. This required access to ice, which had to be hauled in from cold climates by boat, and wasn’t always available, especially in remote places. The picture above shows a cool water spring that was modified long ago into a primitive kind of refrigerator. The structure is made of concrete. When it was in use, it would have had a door to keep cool in and keep animals and insects out, as much as possible.
Just like caves, cool water springs in Arkansas stay close to 56 degrees in the summer – the ambient ground temperature. Anyone that’s spent a summer in Arkansas knows it gets oppressively hot. Having a place you could store milk, eggs, and other perishables would certainly have come in handy. You still come across these old structures if you spend a lot of time out in the woods around the state. This one was photographed near Hot Springs, Arkansas, in the Ouachita Mountains.
This is an anticline exposed on Mc Leod Street, southwest of Hot Springs, Garland County, Arkansas. It’s not unique as, anticlines are common in the Ouachita’s and other mountain ranges throughout the world. Most often though, these structures are large scale and cover expanses of land that can’t be viewed from a human vantage point. When they do form on a scale that’s small enough for human observation, we typically don’t have the benefit of a freshly blasted exposure like this one.
In fact, many times geologists must infer that folds like this exist in places deep underground that no one has or will ever see. That’s why, if you see a geologist on the side of the road, taking something like this in, as in the picture above, just let him have his little moment. The exposure is of deep marine sedimentary deposits of the Stanley Formation.
Igneous rocks are rare in Arkansas, making up about 0.1% of the surface area of the state. Nonetheless, we find some interesting and unusual rocks and minerals within our igneous rocks. The above picture is a pseudohexagonal, zoned, green biotite crystal collected from Magnet Cove, Arkansas just last week. That’s a mouthful!
Magnet cove is a 100 million year old igneous intrusion, now exposed at the surface 12 miles east of Hot Springs, Arkansas. In that little area, over 100 mineral species have been identified, including some that were first discovered there. Students, researchers, and mineral enthusiasts come from all over to visit Magnet Cove, collect samples, and learn about this geologically fascinating place.
Imagine you took a stack of ribbons, compressed it till it buckled into bows, and then tilted the whole stack on its side. That pretty much sums up what you can see in this picture of plunging, folded bedrock at Gulpha Gorge Campground, north of Hot Springs, in the Ouachita Mountains of Arkansas. The bedrock of the Ouachitas was buckled and tilted about 200 million years ago when the South American and North American continents collided – part of the incredible process geologists call plate tectonics.
This is just a couple of wee folds that are exposed at the surface because the bedrock at Gulpha Gorge is novaculite – a really hard rock that doesn’t erode away easily. However, if we could strip the vegetation and civilization away in central Arkansas, we would see that pretty much all the rocks in the region are folded and tilted in similar ways. Some of the folds cover many square miles and can be seen from space on a clear day, and others are no bigger than a speed-bump.