1. About 60 million years ago molten rock forced its way into overlying sedimentary rocks and cooled underground. The cooling igneous rock contracted, fracturing into columns. An earlier intrusion formed the nearby Missouri Buttes. 

2. Over millions of years the sedimentary rock eroded to expose Devil's Tower and accentuate Missouri Buttes. The Tower rises 867 feet from its base, 1,267 above the river, and 5,117 above sea level. The area of its tear-drop shaped top is 1.5 acres. Its base diameter is 1,000 feet.