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The Tertiary in Colorado, US

Tertiary in Colorado map

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Tertiary Fossils
Fossil photos from Tertiary in Colorado

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Paleontology and geology

During the Tertiary, the Rocky Mountains rose, began to erode, and were buried in their own debris. Tropical rainforests grew along the eastern slopes of the young Rockies in the Early Tertiary, and volcanoes rose, shedding debris and ash into the Denver Basin. Mammals, crocodiles, and turtles are the most common animal fossils from these areas. In northwestern Colorado, uplift of the mountains left low-lying areas between the ridges, which filled with water to form huge lakes. Algae accumulated with the lake bottom mud to form oil shales that are the source of fossil fish, leaves, and insects. Cooling later in the Early Tertiary (late Eocene) encouraged the growth of Sequoia forests in the Rockies. Mudflows near Florissant (central Colorado) preserved standing trunks of these huge trees. Large volcanic eruptions in the southern half of the state in the Early to Mid-Tertiary (late Eocene and Oligocene) formed the core of the San Juan Mountains. Ash from these eruptions covered the eastern portion of the state and preserved a variety of mammal fossils, including titanotheres, rhinos, giant pigs, gomphotheres, and bear dogs, to name but a few. Grasslands appeared across much of the state near the end of the Tertiary.

Links to more on the Tertiary in Colorado

Organizations | Education and Exhibits | Research and Collections | Resources


Parks (showing 1 of 1 listings)

Florissant Fossil Beds National Monument: This official site of the National Park Service has information on the rocks and fossils at the monument, as well as information on how and when to get there, fossil images, and educational resources.

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Museums (showing 1 of 1 listings)

Museum of Western Colorado's Dinosaur Journey: Provides information on visiting the museum, as well as the paleontology of western Colorado and surrounding areas.

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Education and Exhibits

Virtual Exhibits (showing 1 of 1 listings)

Ancient Denvers: Ancient Denvers is a virtual exhibit that highlights 13 reconstructions of ancient Colorado landscapes.

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Research and Collections

Researchers (showing 1 of 1 listings)

Florissant Paleontology Collections Database: This database website includes information and photographs for more than 5000 of the published specimens of late Eocene plants and insects from the world-renowned site at Florissant, Colorado. The website allows the user to search the museum collections, the taxonomic placement of the fossils, and the bibliography of references. It is maintained by the National Park Service.

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Field Guides (showing 1 of 1 listings)

Green River Paleobotany Project: This site is geared towards amateurs and professionals who collect fossil plants from the Parachute Creek Member of the Green River Formation in Colorado and Utah. The site provides an identification guide for more than 250 species of fossil plants and encourages collectors to submit images of their own fossils if they think they have found a new species.

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