Editing Florissant Formation (section)

{{Short description|National monument in the United States}}
{{Use mdy dates|date=February 2025}}
{{Infobox rockunit
| name           = Florissant Formation
| image          = Florissant Formation.jpg
| caption        = Florissant Formation at the Clare fossil quarry in [[Florissant, Colorado]]
| type           = [[Formation (geology)|Formation]]
| period         = Eocene
| age            = [[Late Eocene]], {{Geological range|37.2|33.9}}
| prilithology   = [[Shale]]
| otherlithology = 
| namedfor       = [[Florissant, Colorado]]
| namedby        = Cross
| year_ts        = 1894
| region         = [[Colorado]]
| country        = [[United States]]
| coordinates    = {{coord|38.914|-105.287|display=it|format=dec}}
| unitof         = 
| subunits       =
| underlies      = 
| overlies       = [[Wall Mountain Tuff]], [[Pikes Peak Granite]]
| thickness      = {{convert|74|m|ft|abbr=on}}
| extent         =
| area           =
| map            = {{Location map+ | United States#Colorado
| relief = 1
| width   = 250
| float   = center
| places  =
  {{Location map~ | United States#Colorado
  | lat_deg = 38.914
  | lon_deg = -105.287
  | mark = Orange pog.svg
  | marksize = 12
  }}
}}
| map_caption    =
}}
{{Infobox protected area
| name = Florissant Fossil Beds National Monument
| iucn_category = V
| photo = Florissant Fossil Beds National Monument (37356790971).jpg
| photo_caption = The Pioneer House, showing how the original pioneers of the west lived
| map = Colorado#USA
| relief = 1
| map_caption = 
| location = [[Teller County, Colorado|Teller County]], [[Colorado]], United States
| nearest_city = [[Florissant, Colorado]]
| coordinates = {{coord|38.91374|N|105.28627|W|region:US-CO|format=dms|display=inline}}
| coords_ref = <ref>{{cite gnis|191398|Florissant Fossil Beds National Monument|August 8, 2012}}</ref>
| area_acre = 5998
| area_ref = <ref name="area">{{NPS area |year=2011 |access-date=2012-05-13}}</ref>
| authorized = {{start date|1969|08|20}}
| visitation_num = 71,763
| visitation_year = 2017
| visitation_ref = <ref name="visits">{{NPS visitation |access-date=2018-04-09}}</ref>
| governing_body = [[National Park Service]]
| website = [http://www.nps.gov/flfo/index.htm Florissant Fossil Beds National Monument]
}}
The '''Florissant Formation''' is a sedimentary geologic formation outcropping around [[Florissant, Colorado|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 <ref name="McIntoshEtal1992">{{cite journal |last1=McIntosh |first1=W. C. |last2=Geissman |first2=J. W. |last3=Chapin |first3=C. E. |last4=Kunk |first4=M. J. |last5=Henry |first5=C. D. |title=Calibration of the latest Eocene-Oligocene geomagnetic polarity time scale using 40Ar/39Ar dated ignimbrites |journal=Geology |date=1 May 1992 |volume=20 |issue=5 |pages=459–463 |doi=10.1130/0091-7613(1992)020<0459:COTLEO>2.3.CO;2}}</ref>) 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 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<ref name=UCMP>{{cite web|last1=Erwin|first1=Diane M.|last2=Looy|first2=Cindy |title=Florissant Fossil Beds National Monument, Colorado |url=http://www.ucmp.berkeley.edu/science/parks/florissant.php |publisher=UCMP Berkeley |access-date=29 June 2015}}</ref> fossils. The '''Florissant Fossil Beds National Monument''' is a [[National monument (United States)|national monument]] established to preserve and study the geology and history of the area.