Devils Tower rises above the surrounding grassland and Ponderosa pine forests like a rocky sentinel. Northern Plains tribes worshipped at this remarkable geologic formation long before white men wandered into the West; fur trappers, explorers, and settlers alike were awed by the Tower's majesty. In 1906, President Theodore Roosevelt established Devils Tower as our nation's first national monument. Many have gazed at the Tower and wondered, "How did this amazing formation get here? How did it form?"

Geologists agree that Devils Tower was formed by the intrusion (the forcible entry of molten rock into or between other rock formations) of igneous material. What they cannot agree upon is how, exactly, that process took place! Until erosion began its relentless work, Devils Tower was not visible above the overlying sedimentary rocks. But the forces of erosion - particularly that of water - began to wear away the sandstones and shales. The much harder igneous rock survived the onslaught of erosional forces, and the gray columns of Devils Tower began to appear above the surrounding landscape.

As rain and snow continue to erode the sedimentary rocks surrounding the Tower's base, and the Belle Fourche River carries away the debris, more of Devils Tower will be exposed. But at the same time, the Tower itself is slowly being eroded. Rocks are continually breaking off and falling from the steep walls. Rarely do entire columns fall, but, on remote occasions, they do. Piles of rubble - broken columns, boulders, small rocks, and stones - lie at the base of the Tower, indicating that it was, at some time in the past, larger than it is today. Eventually, at some time far in the future, even Devils Tower itself will be eroded away!