Hot Springs National Park is found within the Zig-Zag Mountains, a section of the Ouachita Mountains of central Arkansas and eastern Oklahoma. The name "Zig Zag" comes from the sharply angular folds of the rock when seen from above. The Ouachita mountains were formed during the collision of two tectonic plates around 300 Ma (million years ago). The Appalachian Mountains were formed at about the same time, and were a result of very similar forces. Geologists call the formation of these two mountain systems the Tectonic Orogeny, or mountain-building event.
The area of the park is characterized by steep, mountainous terrain. Although once more jagged, time has reduced the steep peaks of ancient mountains into more gently rolling hills. Visitors will notice that rock layers exposed along bluffs or road-cuts appear to be tilted, or even to stand up straight, rather than lay flat. This tilting of rock layers is a result of extreme forces that "pushed" the rocks into the tilted position, which we can observe today.
The rocks found within the park are sedimentary in nature,including sandstone, shale and a very special rock known as Arkansas Novaculite. This rock is made up of very small quartz crystals, and is quite dense and hard. Arkansas Novaculite is well known for its use as a whetstone, or a stone used to sharpen cutting tools such as knives. The sedimentary rocks that were folded and uplifted to form the Ouachita mountains were originally flat-lying, deposited in a marine, oroceanic setting. Although sedimentary rocks dominate the landscape, igneous bodies can be found by traveling just ten miles to the east.
The hot water that draws visitors to Hot Springs has also impacted the rocks found within the park. Guests might notice narrow, white bands of quartz crystals deposited by hot water as it "punched" its way though local rock. The hot water that emerges at Hot Springs National Park contains a variety of dissolved minerals that come from interaction with rocks both deep withinand near the earth's surface. One of the most noticeable is calcium carbonate. When the hot, or thermal, water reaches the surface, it cools. When this cooling occurs, calcium carbonate, or limestone,is deposited. Visitors will notice a light grey, "spongy" looking rock near the large display spring on Arlington Lawn. This rock, composed of calcium carbonate, is referred to as travertine, or tufa.
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Last updated: January 7, 2016