7 JUNE 2025 WorldWide Drilling Resource® Adapted from Information by the National Park Service Devils Tower National Monument, in northeastern Wyoming, stands tall above the surrounding plains and Ponderosa pine forests, resembling a rocky guardian. Since the late 1800s, geologists have been captivated by this geological marvel, and many question about its formation remain. While there is consensus on much of the Tower’s geological narrative, differing theories persist regarding specific aspects. Designated as a protected site in 1906 due to its scientific significance, Devils Tower continues to be a focal point for research and public admiration. It is composed of an unusual igneous rock known as phonolite porphyry, and boasts the largest example of columnar jointing found anywhere in the world. To deepen our understanding of the processes that shaped the Tower, we must delve back into earth’s ancient history, long before this remarkable feature emerged. The area surrounding Devils Tower is predominately made up of sedimentary rocks, which are created through the solidification of minerals or organic materials, typically brought together by the forces of water or wind. This process, referred to as deposition, is commonly observed in river deltas and coastal regions. Sedimentary rocks often contain fossils, which serve as important indicators of ancient ecosystems. The oldest rocks visible were formed in a shallow inland sea that existed during the Triassic period, approximately 195 to 225 million years ago. This expansive sea once covered a large portion of what is now the central and western United States, playing a significant role in shaping the geological landscape. Geologists generally agree that Devils Tower originated as magma, or molten rock, located deep beneath the earth’s surface. However, there is ongoing debate about the specific processes that led to the cooling of this magma and how it relates to the surrounding geology. Various theories have been proposed to explain the formation of the tower. In the late 1800s, geologists Carpenter and Russell examined the site and concluded the Tower resulted from igneous intrusion, which involves magma forcefully entering through other rock layers. Subsequent geologist sought to provide more redefined explanations. One of the simplest theories is the Devils Tower is a stock - a small body of intrusive rock that solidified underground and was later revealed by erosion. In 1907, scientists Darton and O’Hara suggested it might actually be an eroded remnant of a laccolith. A laccolith is a large, mushroom shaped mass of igneous rock that intrudes between layers of sedimentary rocks. This concept gained traction in the early 1900s, as many studies were conducted on various laccoliths found in the American Southwest. Erosion has significantly transformed the landscape around the Tower. When the Tower first emerged approximately 50 million years ago, it was situated one to two miles beneath the earth’s surface. Between five to ten million years ago, erosion forces began to reveal the Tower. Water, in particular, played a crucial role in eroding and transporting the sedimentary rocks that once covered and surrounded the Tower. The more resilient igneous rock of the Tower resisted erosion, allowing the distinctive gray columns of Devils Tower to rise prominently above the surrounding terrain. As rain and snow persist in eroding the sedimentary rocks surrounding the base of Devils Tower, the Belle Fourche River carries away the resulting debris, gradually revealing more of the Tower. Simultaneously, the Tower itself is subject to slow erosion. This process is evidenced by the large boulder field of fractured columns at the Tower’s base, as well as numerous other rocks scattered along the hillsides below the formation. While small rocks frequently detach from the Tower, no significant column collapses have been recorded in history. The geology of Devils Tower remains somewhat enigmatic for both casual visitors and scientific researchers alike. Although many theories regarding its formation have been explored and understood, the awe-inspiring nature of this site has enchanted people for thousands of years and continues to do so today. Editor’s Note: In between our print issues, the WWDR Team prepares an electronic newsletter called E-News Flash by WorldWide Drilling Resource by WorldWide Drilling Resource®. This newsletter is filled with articles not included in our print issue. Based on readership, this was the most popular article of the month. Get in on the action and subscribe today at: worldwidedrillingresource.com WWDR photos.
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