These 50 well-chosen sites—many on every geologist's bucket list—span Colorado's geologic history from 1.7-billion-year-old rocks of the Black Canyon to the constantly shifting landscape of the Great Sand Dunes. The asteroid-produced iridium-enriched layer that marks the end of the dinosaurs is here, as are insects and petrified wood exquisitely preserved at Florissant Fossil Beds, the pure white marble used in the Lincoln Memorial, mysterious Unaweep Canyon that lacks a river, and colorful mounds of silicious sinter at Pagosa Springs. The Great Unconformity, a famous geologic feature tucked away in a few remote locations in other western states, pops up at seven of the featured sites. The late 1800s rush for precious metals produced a network of roads that crisscross the towering mountains, making Colorado's fascinating geology extremely accessible to the average sightseer. With beautiful photographs and informative figures and maps, this guidebook will help you select a destination and head for the door.