... Its (the tower’s) remarkable structure, its symmetry, and its prominence made it an unfailing object of wonder.... It is a great remarkable obelisk of trachyte, with a columnar structure, giving it a vertically stratiated appearance, and it rises 625 feet almost perpendicular, from its base. Its summit is so entirely inaccessible that the energetic explorer, to whom the ascent of an ordinary difficult crag is but a pleasant pastime, standing at its base could only look upward in despair of ever planting his feet on the top.... Colonel Dodge is generally credited with giving the formation it present name. In his book entitled The Black Hills, published in 1876, he called it “Devils Tower,” explaining “The Indians call this shaft The Bad God’s Tower, a name adopted with proper modification, by our surveyors.” Newton, whose published work on the survey appeared in 1880, explained that the name Bear Lodge (Mateo Tepee) “appears on the earliest map of the region, and though more recently it is said to be known among the Indians as 'the bad god’s tower,’ or in better English, 'the devil’s tower,’ the former name, well applied, is still retained.” However, since that time, the name Devils Tower has been generally used. Geologists, on the other hand, have in some instances continued to use the original name. Over the years there have been changing theories concerning the origin of Devils Tower. The latest belief, based upon the most extensive geological field work yet done, probably will be supported by further study. Briefly stated, about 60 million years ago when the Rocky Mountains were formed, there was similar upheaval which produced the Black Hills and associated mountains. Great masses of very hot, plastic material from within welled up into the earth’s crust. In some instances it reached the surface to produce lava flows or spectacular explosive volcanoes which spread layers of ash many feet over a vast part of the Great Plains. In the Devils Tower vicinity, this slowly upsurging, heated earth substance spent its force before reaching the surface, cooling and becoming solid within the upper layers of the earth. During this process probably a very large mass of it, many miles across, moved within a few thousand feet of the surface. Before it cooled, fingers or branches of pasty-textured material moved upward along lines of weakness in the rock layers near the surface of the earth. Some of these pinched out, while others formed local masses of varying size and shape. Devils Tower and the nearby Missouri Buttes, as we know them today, represent some of these offshoot bodies which solidified in approximately their present size and form at depths of possibly one to two thousand feet beneath the surface. The phonolite porphyry, as the rock of Devils Tower and the Missouri Buttes is known, is very hard. [Illustration: The rock formation of Devils Tower is Phonolite Porphyry. _Courtesy National Park Service._]