Tower National Monument in Wyoming is a short drive northwest of
the Black Hills. The tower rises over 1200 feet above the surrounding
prairie and is the source of much folk lore, including the setting for Close
Encounters of the Third Kind, a movie about direct physical
encounters with intelligent life from outer space.
The tower is igneous rock and some believe it to be the remnant of a volcanic neck. As the hot igneous magma cooled, it shrinks like almost every other physical thing. The cooling caused vertical cracks tat leave the remaining stone in columns or pillars. As weathering causes the rock to break away a tallus pile is formed at the base of the tower. From a distance the tower obscures it's true size. The photo below gives a better idea of the size - those "dots" are full size humans climbing the tower. Devil's Tower is one of the most popular climbing sites in the United States. If you plan to climb it contact the National Park Service (website above) for regulations and permits.