Geology & Fossils
The Great Plains crash into the Rocky Mountains in Colorado, whose fossil heritage also towers above most states. In fact, volcanic ash from volcanoes in the ancient Rockies buried prehistoric mammals far to the east, leaving us some of the most famous fossil sites in the Great Plains.
Paleozoic Era
Fossils of unimaginably ancient marine creatures are sometimes weathered out of ancient rocks high in the Rocky Mountains. But Colorado’s best known fossils are found in a third region, the Colorado Plateau. This vast wilderness of rugged canyons and mesas extends into Utah, New Mexico and Arizona, where the Colorado River carved the Grand Canyon out of it.
Mesozoic Era
The Morrison Formation is a blanket of rocks in the Colorado Plateau that has become world famous as a producer of dinosaur fossils. Part of the Morrison Formation is protected in Dinosaur National Monument, located on the Colorado-Utah border. After Dinosaur National Monument was established, its headquarters were located in the community of Artesia. In 1965 residents renamed their community Dinosaur to attract tourists. But residents didn’t stop there — they also renamed their streets for dinosaurs!
Fossils retrieved from the Morrison Formation represent animals that lived during the Jurassic Period, which lasted from about 208 to 146 million years ago. The Rocky Mountains didn’t yet exist, and much of the Great Plains and western North America were covered with shallow seas.
The Jurassic produced the largest land animals ever. These sauropods, or “long-necks,” included Apatosaurus (alias Brontosaurus), Diplodocus, and Brachiosaurus. Jurassic beasts also include the state fossils of Colorado and neighboring Utah, Stegosaurus and Allosaurus. Colorado is the world headquarters for stegosaur fossils.
Cenozoic Era
Fossils buried under sediments eroded from Colorado’s mountains are found in mountain valleys and basins. Uinta Basin cradled a vast lake which left coal and plant and animal fossils.
West of Pikes Peak, another lake formed, dammed by a lava flow from a nearby volcanic field. Fine volcanic ash falling into this lake during the Oligocene Epoch preserved the trunks and leaves of many plants as well as abundant insects, fish, and occasional mammals. Florissant has revealed massive redwood stumps and tiny butterflies, complete with antennae, legs, hairs and wing patterns. This fabulous site is now protected in Florissant Fossil Beds National Monument. Redwoods, poplar, hackberry, and pine suggest a warmer climate than today.
The ruins of Indian dwellings preserved in Colorado’s Mesa Verde National Park and Hovenweep and Yucca House national monuments are evidence of a much more recent age. Perhaps one day in the distant future, the ruins of the city of Denver will be protected in a national park!
Fossils in Our Lives
Place names like Boncarbon, Coal Creek, Coaldale, Coalmont, and Cokedale are evidence of Colorado’s wealth of fossil fuels, including coal, petroleum, natural gas, and oil shale. Vast reserves of bituminous coal exist in both northern and southern Colorado. Oil and gas are found in the west and east.
Oil shale could become Colorado’s richest mineral resource. It contains kerogen, a gummy, bituminous substance that yields oil when heated. The richest deposits are in Rio Blanco and Garfield counties in northwest Colorado. The U.S. Geological Survey estimates that these deposits and others that extend into Utah and Wyoming contain well over 50 times the United States’ proven oil reserves.
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