The Geologic Story of Colorado National Monument / Revised Edition

by Stanley William Lohman

The Age of Reptiles

All the layers of sedimentary rocks preserved in the Monument above the dark Proterozoic ones were deposited by wind and water during the Mesozoic Era. This long era has been called the age of reptiles, for reptiles, including dinosaurs (meaning terrible lizards), were then the dominant land animals. The Mesozoic Era has been divided into three parts—the Triassic, Jurassic, and Cretaceous Periods. Rocks of each of these periods crop out in the Monument.