Geology of the Ozarks
What is the Ozark Plateau?
The Ozark Plateau is a rugged, hilly landscape that spans across northern Arkansas, southern Missouri, northeastern Oklahoma, and southeastern Kansas. The region is primarily composed of several smaller plateaus, including the Salem Plateau, Springfield Plateau, and Boston Plateau. This area is shaped significantly by water and the underlying geology, which is dominated by sedimentary rocks such as limestone, dolostone, and sandstone.
Image_1 Tosborn at English Wikipedia Public Domain
Karst Topography
One of the most striking features of the Ozarks is its karst landscape, characterized by caves, springs, and disappearing streams. This type of landscape is formed when slightly acidic water erodes away easily dissolved bedrock, such as limestone and dolomite, which are abundant in the Ozarks. The erosion of these rocks has created underground systems that support unique ecosystems. Karst systems also form excellent aquifers, supplying freshwater to plants, animals, and people alike. Although karst landscapes cover only about 20% of the U.S., they provide 40% of its freshwater.
Figure 1 in Taylor, Charles J., and Earl A. Greene. "Hydrogeologic characterization and methods used in the investigation of karst hydrology." US Geological Survey (2008). Chapter 3 of Field Techniques for Estimating Water Fluxes Between Surface Water and Ground Water, Edited by Donald O. Rosenberry and James W. LaBaugh, Techniques and Methods 4–D2. Available from USGS at https://pubs.usgs.gov/tm/04d02/pdf/TM4-D2-chap3.pdf
Rock Types in the Ozarks
The Ozarks are mainly composed of sedimentary rocks, which formed over millions of years as layers of eroded materials and dead marine organisms compressed into solid rock. The primary rock types found here are:
Limestone: Formed from marine organisms that used calcite to create their shells, limestone reacts with acidic water, making it vulnerable to erosion, which is why it plays a central role in the formation of karst features. Limestone is typically gray or white and scratches easily. Fossils are often found embedded in this rock.
Image_limestone Office of the State Geologist Blog https://arkansasgeological.wordpress.com/2014/02/07/geopic-of-the-week-fenestrate-bryozoan-in-limestone/
The Rock Cycle
The materials that make up the rocks in the Ozarks are part of the continuous rock cycle, where rocks transform from one type to another over millions of years. Here's a simplified overview:
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Igneous rock forms when molten magma from beneath the Earth's crust cools and solidifies.
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Sedimentary rock forms when particles from eroded rocks or dead organisms accumulate in layers and become compacted over time.
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Metamorphic rock forms when existing rocks are subjected to heat and pressure deep underground, causing them to change into new types of rock.
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Over time, rocks are weathered, eroded, and recycled, continuing the cycle endlessly.
Image_rockcycle c National Geographic https://education.nationalgeographic.org/resource/rock-cycle/
The Geological History of the Ozarks
The story of the Ozarks begins in the Paleozoic Era, about 540-248 million years ago, when the land that is now Arkansas was under a shallow, warm sea. This sea was teeming with life, much like the modern-day Bahamas. When marine organisms died, their remains sank to the ocean floor (a process known as marine snow), where they mixed with sediments and eventually compressed into the limestone and dolostone we see in the Ozarks today.
During this time, two small landmasses—Llanoria to the south and the St. Francis Mountains to the north—flanked the Ozarks. As Llanoria eroded, sediments collected and eventually formed the sandstone and shale that make up the nearby Ouachita Mountains.
With the retreat of the sea (caused by the formation of glaciers) and subsequent uplift events as North and South America slowly collided, the Ozark Plateau rose. The collision caused layers of rock to be pushed up and eroded over time, forming the high-elevation flat tops characteristic of the region today.
Images:
paleozoic period c Figure 8 from Guccione, 1993
ozarkplateauuplift C Figure 16 from Guccione, 1993
ozarkplateau2 C Figure 21 from Guccione, 1993
ozarkplateau3 C Figure 23 from Guccione, 1993
ozarkplateau4 C Figure 25 from Guccione, 1993
Why Geology Matters
Geology shapes the land around us, and in the Ozarks, it affects everything from the types of plants that grow here to the animals that live in the region. Different rocks release specific minerals into the soil as they erode, influencing plant growth. For example, certain plants thrive in calcium-rich soils derived from limestone, which in turn affects the types of animals that rely on those plants for food. Geology also impacts the water content in the soil, how shaded certain areas are, and the shape of the land itself, from steep hills to rolling valleys.
See our other exciting web pages for more information on the amazing variety of Ozark flora and fauna!
Conclusion
The geology of the Ozarks is more than just rocks—it’s the foundation of the entire ecosystem, shaping everything from underground aquifers to the plants and animals that call this rugged landscape home. The interaction of water and rock, combined with millions of years of geological processes, has created the beautiful and ecologically rich Ozark Plateau region we know today.
Additional Resources
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Geologic History of Arkansas Through Time and Space by Margaret J. Guccione (1993, 66p)
A detailed exploration of the geologic history of Arkansas, offering insights into how the state's landforms were shaped over time.
Download the PDF here -
Geologic Timescale and Brief History of Arkansas Formation
This resource provides a simplified geologic timescale and an overview of the processes that created the landforms seen in Arkansas today.
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The Office of the State Geologist (Formerly Arkansas Geological Survey) This resource provides a plethora of information about Arkansas geology! There are detailed geologic maps, publications, educational resources, and so much more. https://www.geology.arkansas.gov/
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Karst in the Ozarks A project of the Ozarks Resource Center providing educational resources about our caves, springs, and underground water. https://karstintheozarks.org/
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Minerals-Geology-U.S. National Park Service A general overview of the properties and types of minerals. You will see from this site one may also link to several other pages about aspects of geology. https://www.nps.gov/subjects/geology/minerals.htm
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Rocks, Minerals, and Fossils A page by the Missouri Department of Conservation detailing classifications of different types of rocks and minerals, as well as information about fossils. There are also links to several other interesting geology topics, such as caves, sinkholes, and the New Madrid Seizmic Zone. https://dnr.mo.gov/land-geology/geology/rocks-minerals-fossils