The Devil's Hole cave is developed in the Keyser Member of the Helderberg limestone.
Devils Tower
towers over surrounding grasslands and ponderosa pine forests like a rocky sentinel. Geologists have studied the formation since the late 19th century, and today they still wonder how it formed. Although much of the Tower's geological history is in agreement, the theories differ on certain details.Protected in 1906 for its scientific value, Devils Tower remains a place of scientific study and public wonder. We know that the Tower is formed by a rare igneous rock, a porphyry phonolite, and is the largest example of a columnar union in the world. To better understand the processes that shaped the Tower, we review the history of the Earth, long before this unique feature took shape. Two other geological units are found in the monument, but they are poorly exposed.
The lake member of the Sundance Formation is the yellowish unit exposed along the road near the visitor center, and the member of the Sundance Redwater shale is a gray unit made primarily of limestone. It is usually covered by vegetation or the astragalus of the Tower, but remains can be seen in the highest areas of the monument (not including the Tower). This is a marine unit deposited about 163 million years ago. Other younger formations were present in the past, such as the famous Morrison Formation of the Late Jurassic and the Lakota Formation of the Lower Cretaceous, but they have been lost due to the same erosion that exposed and sculpted the Tower.
Scattered fragments of hard white quartzite are remnants of the Lakota Formation. There are also isolated chunks of an unusual type of rock formed from rock fragments in an igneous matrix, sometimes called an “agglomerate”. This type of rock is related to the formation of the Tower and allows us to glimpse the bedrock that lies below the surface. The name “Devil's Den” refers to a 600 million-year-old cave formation comprised of several layers of rock which contain many large rooms.
Formed by the collision of rock incrustations from Appalachia and Piedmont, this cave is mainly metamorphic schist, granite with deposits of mica and pyrite, and even 45 encrustations of solid quartz bands. The nature reserve surrounding the cave offers 280 acres of land, including mature hardwood forests, felled plateaus and shrub scrub. A strenuous 1.5-mile circular trail crosses most of these habitats and has a small branch that leads to the spectacular cave. However, because the cave is unstable, public access is no longer allowed. The red-eyed vireo, the green, black-throated hooded warbler, the common thrush, the scarlet tanager and the indigo flag are common throughout the summer.
Ironically, the erosion that exposed the Tower also erased the evidence needed to determine which theory about the formation of the Devil's Tower is correct. The columns of Devils Tower, which rise hundreds of feet into the air and extend up to 10 feet wide, are truly spectacular. Some of these wooden stakes remain intact and can be seen in the tower when you walk the 1.3-mile (2.1 km) Tower Trail at Devils Tower National Monument. Wooden Leg, a Cheyenne from the north, related another legend told to him by an old man when they passed through the Devil's Tower together between 1866 and 1868. Geologists Carpenter and Russell studied the Devil's Tower in the late 19th century and concluded that the Tower was formed by igneous intrusion (the forced entry of magma through other layers of rock).
As rain and snow continue to erode the sedimentary rocks surrounding the base of the Tower, more parts of Devils Tower will be exposed. The children make the sisters drive the bear to the Devil's Tower and trick him into believing that they have climbed the rock. Geologists agree that Devils Tower began as magma, or molten rock buried under the Earth's surface. In 1907, scientists Darton and O'Hara decided that Devils Tower must be an eroded remnant of a laccolyte.
As rain and snow continue to erode the sedimentary rocks surrounding the base of the Tower and the Belle Fourche River carries away the debris, more parts of Devils Tower will be exposed. The Tower's harder igneous rock is more resistant to erosion, and the gray columns of the Devil's Tower began to stand out from the surrounding landscape. Geologists Carpenter and Russell studied the Devil's Tower at the end of the 19th century and came to the conclusion that it was formed by an igneous intrusion. However, the columnar junction of Devils Tower is the largest and most spectacular example of this fascinating geological phenomenon.
Pohd-lohk, an elderly Kiowa, gave Scott Momaday (Kiowa) the name Tsoai-talee (Child of the Rock Tree), and linked the boy to the myth of the Tower Bear of the Devil.
