Devils Tower
Teddy Roosevelt declared Devils Tower America's first national monument, and Steve Spielberg decided to land a UFO on top of it in "Close Encounters of the Third Kind. Long before either man thrust the natural landmark into the spotlight, more than 20 Native-American tribes held the site sacred -- including the Lakota people who dubbed it "Bear Lodge."
While its exact origins are unclear, many geologists believe the enormous column of igneous rock is an intrusion: a column of molten rock pushed up from the inner Earth through sedimentary rock layers. It's unclear whether the intrusion cooled before or after it breached the surface, but the vertical furrows indicate that cooling and contraction took place.
Geologists suspect the northeastern Wyoming tower formed more than 50 million years ago and remained buried beneath the ground up until roughly 2 million years ago [source: SERC]. Today, Devils Tower is a popular tourist destination, and licensed climbers can even scale the monolith for an unforgettable view.
Read More