Editing Florissant Formation (section)

===Thirtynine Mile Volcanic Field===
[[File:Big Stump.jpg|thumb|upright|right|A large petrified stump of ''[[Sequoia affinis]]'' at Florissant Fossil Beds National Monument<ref name = "website">Florissant Fossil Beds. 2012. National Park Service. 5 November 2012. http://www.nps.gov/flfo/index.htm</ref>]]
Around 25–30 kilometers to the southwest, a series of stratovolcanoes, similar to modern day volcanoes like Mt. St Helens, developed and erupted periodically. Called the [[Guffey, Colorado|Guffey]] volcanic center, within the larger [[Thirtynine Mile volcanic field]], the volcano had eruptions that included domes, lava flows, and pyroclastic events.<ref>Chapin, C. E., & Epis, R. C. (1964). Some Stratigraphic and Structural Features of the Thirtynine Mile Volcanic Field, Central Colorado. The Mountain Geologist, V. 1, p. 145-159</ref><ref>Wobus, R. A. et al. (1990). Geochemistry of high-potassium rocks from the mid-Tertiary Guffey volcanic center, Thirtynine Mile volcanic field, central Colorado, Geology, V. 18, No 7, p. 642-445</ref> Ash from these events settled throughout the area and lahars flowed down the valleys. The ash that settled created the tuff, and the lahars formed the mudstones and the conglomerates of the Florissant formation.

The Florissant was deposited in a paleovalley after one of the lahars dammed it up. The resulting lake became as large as 36&nbsp;km<sup>2</sup>.<ref name = "Veach, 2008" /> There were two cycles of lake environments. The first one created the lower shale unit, while the second lake created the middle and upper shale units.<ref name="book"/>
Eventually, the volcanoes became dormant and started to erode away. Over time, the volcanoes became so eroded that there are no more obvious signs of them on the surface. Instead, the Eocene erosional surface is the only remnant of the area's volcanoes.<ref name = "Gregory, 1992" />