The geology, fossils, and human stories of Florissant Fossil Beds National Monument are part of a common geologic heritage. The layers of rock beneath this valley contain one of the richest fossil deposits in the world. They hold clues of unexpected environments and life that existed here during a time called the late Eocene.
The Florissant Formation is a sedimentary geologic formation outcropping around Florissant, Teller County, Colorado. The formation is noted for the abundant and exceptionally preserved insect and plant fossils that are found in the mudstones and shales. Based on argon radiometric dating, the formation is Eocene, approximately 34 million years old, in age and has been interpreted as a lake environment.
The fossils have been preserved because of the interaction of the volcanic ash from the nearby Thirtynine Mile volcanic field with diatoms, or algae, in the lake, causing a diatom bloom. As the diatoms fell to the bottom of the lake, any plants or animals that had recently died were preserved by the diatom falls. Fine layers of clays and muds interspersed with layers of ash form "paper shales" holding beautifully-preserved fossils.
The name Florissant comes from the French word for flowering. In the late 19th century tourist and excavators came to this location to observe the wildlife and collect samples for collections and study. The Petrified Forest, which is one of the main attractions at the monument today, lost much of its mass due to collectors removing large amounts of petrified wood from the site.
During the 1860s and 1870s the area was mapped by geologists for the first time. Geologists of the Hayden Survey visited the area in the early 1870s, and fossil plants from the beds were described by Leo Lesquereux, fossil insects by Samuel Hubbard Scudder, and vertebrate fossils by Edward Drinker Cope. The formation was first formally named as the Florissant Lake Beds by Charles Whitman Cross in 1894.
In 1969, the Florissant Fossil Bed National Monument was established after a long legal battle between local land owners and the federal government. Today, the park receives approximately 60,000 visitors a year, and is the site of ongoing paleontological investigations.
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