Now a sea of homes, it's hard to imagine that Highlands Ranch, on the southern edge of metropolitan Denver, actually was once a ranch, much less a tropical rainforest or seashore! Rapid population growth and development have transformed the region. These changes have played out against the seemingly constant backdrop of the Front Range and its signature geologic features: the Boulder Flatirons, the Dakota Hogback, Garden of the Gods, the Continental Divide. But the entire human history of the Front Range is barely a blip in the context of geologic history. Over eons of time, astonishingly different Denvers—mountains, deserts, seas, rainforests—have come and gone.

What will future Denvers be like millions of years from now? Because human activity is now capable of impacting the natural world on a global scale, the answer will likely depend on the choices we make today.

Photo credit: Kirk R. Johnson, curator of paleontology