• Massive petrified redwood stumps

    Florissant Fossil Beds

    National Monument Colorado

Online Curriculum - Geology (Unit 2)

Igneous Rocks

Igneous rocks, such as the Wall Mountain Tuff and the Pikes Peak Granite, are formed by geologic processes beginning deep within the Earth. An igneous rock begins developing as molten magma deep within the Earth. Magma can take one of two paths: it can remain deep underground and cool slowly to become an intrusive igneous rock such as granite, or it can be erupted onto the Earth's surface either as lava or more explosively as pyroclastic eruptions of tuff, ash, and pumice (as seen at Mt. St. Helens).

A complex of stratovolcanoes near the modern-day town of Guffey, Colorado, about 15 - 18 miles southwest of Florissant played an important role in the formation of ancient Lake Florissant, as well as the deposition of the Florissant Formation.

Idealized cross-section of the late Eocene landscape of Guffey and Florissant (Joseph Hall).
Idealized cross-section of the late Eocene landscape of Guffey and Florissant (Joseph Hall).

Sedimentary Rocks

Over time, most rocks weather and erode due to chemical and physical processes such as water action and other factors. The end product of this erosion is sediment, which ultimately is deposited in a basin such as a river, stream, pond, lake, or ocean. Sediments can range from large boulders to clay only visible under the highest-powered microscope. Over time, these sediments can become cemented and hardened together by the process of lithification. The result of lithification of sediments is sedimentary rock, such as the paper shales of the Florissant Formation.

Types of Sedimentary Environments

Did You Know?


One of the most common fossils found in the Florissant Formation include leaves from Fagopsis, which is an extinct member of the beech family. This image is protected by copyright. All rights reserved. To learn