Colorado fossils have enriched museums around the world for nearly 150 years.


Florissant Fossil Beds National Monument protects a site where ash from volcanic eruptions 34 million years ago trapped and preserved an entire ecosystem. Paleontologists have collected more than 60,000 specimens, including 140 plant species and 1,100 insect species. The worlds first roses, flies preserved in such detail that the lenses in each eye can be counted, and massive, petrified redwood stumps may all be found at Florissant.

Fossil wasp from Florissant national monument

48 million-year-old Beetle from the Green River formation

Pictured are a fossilized wasp from Florissant National Monument and a forty-eight-million-year-old beetle from the Green River Formation.


Colorado’s dinosaur fossils cover a wide spectrum – coming from all three periods of the Mesozoic Era – and representing all six dinosaur groups and twelve of the fifteen known dinosaur families. Specimens recovered in the 1800s are still some of the best fossils of two of the groups of dinosaurs.

Adult and juvenile Stegosaurus skeletons at the Denver Museum of nature and science.

Pictured are an adult and juvenile Stegosaurus, mounted dinosaur skeletons at the Denver Museum of Nature and Science.


In 1887, strata near Canon City were found to contain the world’s oldest known vertebrates. The area now known as the Indian Springs Trace Fossil Natural Area is also unusually rich in traces of animals that lived 450 million years ago. Study of trace fossils such as the tracks and burrow patterns of horseshoe crabs, brachiopods, and trilobites give clues to the behavior of creatures living in the mudflats of an ancient tidal lagoon.

Contemporary Fossil Discoveries

Despite 150 years of enthusiastic collecting in Colorado, it is impressive that important fossil discoveries continue to be made. In the past thirty years, scientists have unearthed the world’s first articulated Stegosaurus skeleton; three of the world’s four largest dinosaurs; the largest dinosaur trackway in North America; a hue palm forest; one of the world’s most diverse leaf fossil sites; an eight-foot long mammoth tusk; and Tyrannosaurus rex bones. In 2010 a marvelous treasure trove of ice-age mammals and plants was discovered above Snowmass Village. For a list of some Colorado fossil sites, click here.

Notable Fossil Rock Units

Three Colorado rock units are world famous for their treasure troves of fossils: the White River Formation in northeastern Colorado, the Green River Formation in the northwestern part of the state, and the Morrison Formation found in numerous locations around the state. The White River Formation is one of the richest fossil mammal beds in the world, containing fossils of camels, elephants, horses, mammoths, hippos, and rhinoceroses. The famous Green River Formation contains beautiful fossils of fish, scorpions, beetles, frogs, hundreds of insect species, and more than 100 species of trees. The several-hundred-foot-thick layers of the Morrison Formation yield dinosaur bones and tracks including the world’s largest and smallest dinosaurs.


Paleontology is the study of ancient life.

Common invertebrate fossils found in the Pierre shale.

It looks like a fossil, but it is not. These are inorganic dendrites made of manganese dioxide

Pictured above: Common invertebrate fossils found in the Pierre shale. Inorganic dendrites made of manganese dioxide.

Fossil giant Sequoia tree at Florissant national monument

Stegosaurus fending off a T Rex at the Denver Museum of Nature and Science

Fossil leaf from the Castle rock rain forest site

Pictured from top to bottom: Sequoia stump from Florissant National Monument; Stegosaurus fending off a T. Rex at the Denver Museum of Nature and Science; Fossil leaf from the Castle rock rain forest site.