Florissant Fossil Beds National Monument (Part 1)

Florissant Fossil Beds National Monument protects 6,278 acres around a Late Eocene fossil deposit in Florissant, CO. It is one of the richest fossil sites in the world, particularly noted for the insect, arachnid, and plant fossils preserved in its paper shales as well as its petrified redwood stumps. At least 1,700 fossil species have been described from Florissant, including 1,500 arthropods and 150 plants. Over 50,000 specimens collected from the site are housed in about 20 museums and universities across the United States and United Kingdom.

Geologic Trail crosses a bridge over Grape Creek in front of Pikes Peak Granite that formed over 1.08 billion years ago during the Precambrian Era. The formation is a batholith, a mass of magma that cooled and hardened underground. About 70-40 million years ago, a mountain building event known as the Laramide Orogeny formed the Rocky Mountains and erosion eventually exposed the Pikes Peak Granite. The formation is about 25 miles wide and stretches 80 miles in length from Castle Rock, CO to just south of Colorado Springs, CO. In 1994, an intern found mammoth (Mammuthussp.) fossils near here which dated to about 49,830 years ago within the Quaternary Period. At 8,400 feet, this is one of the highest elevations to yield ice age mammoth fossils.

This Wall Mountain Tuff formed about 36.73 million years ago as the result of a pyroclastic flow from a caldera near Mount Princeton 50 miles to the west. A pyroclastic flow is a superheated cloud of ash, gases, and volcanic matter ejected during an eruption. The ash and pumice cooled to form rhyolitic welded tuff that covered this area until streams eroded most of it out of the valley. Erosional processes also left behind a layer of granular granite fragments. Between the Wall Mountain Tuff and the Pikes Peak Granite underneath is an unconformity, or a gap in the rock sequence, representing about 1.04 billion years of rock layers that were lost due to erosion.

Geologic Trail ends at an overlook of the Florissant Valley. During the Late Eocene, a cluster of volcanoes called the Guffey volcanic center existed about 15 miles to the southwest. Loose ash and debris that accumulated on the sides of the volcanoes mixed with rainfall to create mudflows called lahars that flowed down into the valley at speeds up to 80-90 miles per hour. About 34.07 million years ago, one of these lahars dammed a stream that flowed through the valley to form Lake Florissant. Paper shales rich in fossils were deposited on the lake bottom in alternating layers with tuffs from ongoing eruptions to form the lower shale unit of the Florissant Formation. As shale and ash filled the lake, it transformed into a series of small streams along which giant redwoods grew. A massive lahar then flowed into the stream valley and covered the tree trunks in up to 15 feet of mud, suffocating the roots of oxygen, killing the trees, and contributing to the fossilization of the stumps. Sediments deposited by the streams along with this lahar form the lower mudstone unit of the Florissant Formation.

The Outdoor Exhibit Area showcases some of the monument’s petrified redwood stumps. Florissant boasts some of the largest petrified stumps by diameter in the world, with the largest measuring about 14 feet. At least 30 petrified stumps are known within the boundaries of the monument although many were reburied by the National Park Service for their preservation. A few of the stumps are angiosperms but most have been identified as Sequoia affinis, an extinct relative of the modern coastal redwood (Sequoia sempervirens). Many of these trees may have been 500-700 years old and over 200 feet tall when they were killed. The thin metal bands secured around the stumps prevent loose pieces from falling off.

After the redwoods were buried, another lahar dammed the stream valley six miles to the south and Lake Florissant formed again, growing to be about a mile wide and 12.5 miles long. For thousands of years, paper shales accumulated in alternating layers with tuffs from volcanic activity to form the middle shale unit of the Florissant Formation. A large lahar nearly filled the lake, depositing the caprock conglomerate unit, but paper shale and tuff continued to accumulate and formed the upper shale unit over it. A large-scale eruption of pumice and ash from the Guffey volcanic center deposited the upper pumice conglomerate unit and finally ended the existence of Lake Florissant. The volcanoes became dormant and eroded away over time as did most rocks deposited between the Oligocene and the Pleistocene. Since the start of the Quaternary Period 2.58 million years ago, streams weathered Pikes Peak Granite, volcanic rocks, and mud into the terrace gravels that now cover much of the area.

This map shows the range of redwoods across the world during the Late Eocene. About 34.07 million years ago, the climate of Florissant was warmer and wetter, likely temperate to subtropical with a winter dry season. Mean annual temperature estimates from different studies range anywhere between 51.26-64.4°F (10.7-18°C), which is much higher than the 39.2°F (4°C) of today. Most of the precipitation would have occurred in late spring to early summer amounting to about 50-80 cm per year, which is also higher than the 38 cm average of today. Tree-ring analysis reveals that the environmental conditions at Florissant when the redwoods were buried were more favorable for their growth than the current climate of California where coastal redwoods grow today.

The Redwood Trio are three fossilized redwood stumps that grew out of the trunk of a single older tree. The original parent redwood broke or burned and three genetically identical clones sprouted from its roots. This method of reproduction, known as stump sprouting, is seen in modern coastal redwoods. 

The petrified stumps were fossilized via permineralization. Silica from volcanic matter in the lahar dissolved into water that flowed to the buried stumps where the silica slowly precipitated into the wood cells, creating an internal cast. As the organic matter decayed, it was replaced by silica until the stumps were entirely stone.

This diagram illustrates the rock layers of the monument from the Pikes Peak Granite upwards to the Wall Mountain Tuff, the six units of the Florissant Formation including the lower shale, lower mudstone, middle shale, caprock conglomerate, upper shale, and upper pumice conglomerate, and finally the overlying terrace gravels. The Tallahassee Creek Formation cannot be seen within the boundaries of the monument and is located further south.

Although indigenous peoples may have lived here as long as 10,000 years ago, the oldest evidence of occupation in the monument is a Midland Point discovered in 2017 that dates to between 6,000-8,000 years ago. Native Americans traditionally associated with this area were forcibly relocated to reservations in the late 1800s. Eighteen modern tribes claim this area as part of their historical range including the Southern Ute Indian Tribe, Jicarilla Apache Nation, Ute Mountain Ute Tribe, Navajo Nation, Assiniboine & Sioux Tribe, Kiowa, Comanche, Northern Cheyenne, Ohkay Owingeh, Pueblo of Acoma, Pueblo of Cochiti, Pueblo of San Ildefonso, Pueblo of Santa Clara, Pueblo of Taos, Pueblo of Zuni, White Mesa Ute, Arapaho of the Wind River Reservation, and Ute Tribe Uintah and Ouray Reservations.

The fossil beds area was unsettled and known as the valley of Twin Creek until James Castello established a trading post there in 1870 and renamed the valley Florissant after his hometown in Missouri. The name Florissant comes from the word floraison, which is French for “flowering.” In 1872, David Long and his family became the first to settle on land within the current boundaries of Florissant Fossil Beds National Monument. Those settling in the Florissant area during this time squatted on the land hoping to someday apply for the title. Although the Homestead Act of 1862 enabled settlers to claim 160 acres of federal land if they lived on the property and improved it for five years, the land needed to be government surveyed. To accomplish this, the government sponsored the Four Great Surveys of the West: The U.S. Geological Exploration of the Fortieth Parallel led by Clarence King (1867-1872), the U.S. Geological and Geographical Survey of the Territories led by Ferdinand Vandeveer Hayden (1867-1878), the U.S. Geographical and Geological Survey of the Rocky Mountain Region led by John Wesley Powell (1869-1879), and the U.S. Geographical Survey West of the One Hundredth Meridian led by Lieutenant George Montague Wheeler (1872-1879). 

Several Hayden Survey scientists visited and collected specimens at Florissant in the 1870s. In 1873, geologist Albert Charles Peale first noted the lake deposit fossils as well as 20-30 petrified stumps in the valley. That same year, paleobotanist Charles Léo Lesquereux published the first scientific paper about the fossils. Lesquereux described over 100 new fossil plant species from Florissant and much of his collection now resides at the Smithsonian National Museum of Natural History and the Peabody Museum of Natural History at Yale. Paleontologists Joseph Leidy and Edward Drinker Cope studied the vertebrate fossils, with Cope describing some fishes and a shorebird from 1874-1883.

In 1874, Adam and Charlotte Hill moved to the Florissant Valley and established Petrified Stump Ranch. Charlotte took interest in the fossils and amassed a large collection of well-preserved plant and insect fossils. In 1877, a group of students and professors known as the Princeton Scientific Expedition collected fossils at Florissant. They met with Charlotte and were impressed by her assemblage of fossils, all of which were new species. After acquiring some of her fossils and excavating others, they sent the plant fossils to Lesquereux for description. Insect fossils were sent to Hayden Survey paleoentomologist Samuel Scudder who had published papers the year prior based on specimens collected from Florissant. A few of the fossil plant and insect species were named in honor of Charlotte Hill. A month after the Princeton Scientific Expedition, Scudder visited Florissant with geologist Arthur Lakes. Charlotte gave Scudder some of her fossils and he collected others near the Big Stump. In 1878, Arthur Lakes produced the first geologic map of the Florissant valley. Students Henry Fairfield Osborn, William Berryman Scott, and Frank Speir Jr. of the Princeton Scientific Expedition also described the new fossil fish species Trichophanes copei collected at Florissant. Osborn would achieve great notoriety in 1905 for being the first to describe Tyrannosaurus rex based on a partial skeleton discovered in Montana. Samuel Scudder described about 600 new species of fossil insects from Florissant over 23 papers and the 1890 monograph The Tertiary Insects of North America. Most of his insect fossils are now housed at the Harvard University Museum of Comparative Zoology. 

After the Hayden Survey concluded in 1878, Adeline Hornbek claimed the first homestead in the fossil beds area. The Hornbek Homestead still stands at its original location within the boundaries of the monument. By 1880, at least 35 families claimed homesteads in the Florissant area. In 1883, Adam and Charlotte Hill sold the Petrified Stump Ranch to the Colorado Museum Association, a consortium of Denver businessmen led by Charlotte’s brother John Davis Coplen. It was eventually renamed Coplen Petrified Forest and access was restricted to scientists and visitors with special permission in the hopes that someday the site would be made a state museum. In 1887, the Colorado Midland Railway opened a line to Florissant, enabling tourists and excavators to easily collect fossils and remove large amounts of petrified wood in the valley. In 1894, Charles Whitman Cross named the fossil-bearing layer of the area the Florissant Lake Beds, later renamed the Florissant Formation in 2001. In 1898, Walter Charles George Kirchner published a summary listing of Florissant plant species in which he described 12 new species. In 1903, the Colorado Museum Association dissolved and John Davis Coplen later bought out the surviving investors for full ownership of Coplen Petrified Forest. 

During the summers of 1906-1908, entomologist Theodore Dru Alison Cockerell and his wife, Wilmatte, led three expeditions to Florissant, collecting a multitude of insect, spider, plant, and mollusk fossils. Four fossil tsetse fly species described by Cockerell supported the idea that the climate at Florissant must once have been similar to that of modern tsetse fly habitat in tropical Africa. Cockerell described 333 new species and published 140 papers on Florissant fossils over his career. The bulk of his collections are kept by the University of Colorado Museum of Natural History. Cockerell’s initial finds kicked off a new wave of scientific interest in Florissant. Between 1906-1910, entomologist Charles Thomas Brues produced six publications on Florissant fossils, with five on Hymenoptera (bees and wasps) and one on a grass. From 1908-1920, entomologist Henry Frederick Wickham published 15 studies on Coleoptera (beetles) fossils from Florissant. He dug a single trench 20 feet long and six feet deep at Florissant in 1912 that yielded over 90 species of beetles, 40 of which were new to science. His collections are now housed at the Smithsonian Natural Museum of Natural History. In 1916, paleobotanist Frank Hall Knowlton also contributed a publication on Florissant plant fossils.

The Big Stump is a petrified redwood stump that measures 12 feet in diameter and 38 feet in circumference. At the time of its death, the tree may have been 500-1,000 years old and stood over 230 feet tall. The lahar that killed the tree became part of the lower mudstone unit that can be seen directly behind the stump. Above that is the middle shale unit deposited at the bottom of Lake Florissant. At the top of the hill is the caprock conglomerate unit deposited by a large lahar into the lake. The rusty broken saw blades stuck at the top of the Big Stump were left behind after the Colorado Museum Association tried sawing it into pieces that could be transported for display at the 1893 Chicago World’s Fair.

In 1922, John Davis Coplen opened Coplen Petrified Forest as a tourist attraction. Between 1922-1924, he relocated the abandoned Colorado Midland Railway station from Florissant to the property and renovated it into a hotel. Visitors could see the Big Stump, fossil exhibits, and a fireplace made from petrified wood. In 1924, David Henderson opened a competing enterprise on the adjacent property, which was known as New Petrified Forest before being renamed Henderson Petrified Forest. The main draws of this business were the Redwood Trio and a museum that later became a visitor center after the monument was established. In 1927, Palmer and Agnes Singer purchased Coplen Petrified Forest and renamed it Colorado Petrified Forest. The family also opened the Broncho Dude Ranch and operated both businesses until 1973, only closing temporarily during World War II.

In 1930, paleoentomologist Frank Morton Carpenter published the monograph The fossil ants of North America in which he described 28 new fossil ant species from specimens he collected at Florissant in 1927. He later recorded most of the world’s fossil insect genera in his 1992 Treatise on Invertebrate Paleontology, which included listings for 765 genera described from Florissant. In 1936 and 1937, paleobotanist Harry Dunlap MacGinitie excavated fossils from three sites at Florissant. He named about 20 new species in his 1953 monograph Fossil Plants of the Florissant Beds, Colorado and revised names for fossil plants from Florissant previously described by Lesquereux, Cockerell, Kirchner, Knowlton, and others. He was also the first to compare the plant fossils with living species to make inferences about past ecology, climate, and elevation. MacGinitie’s collections now reside at the University of California Museum of Paleontology. Between 1937-1941, entomologist Maurice Theodore James published on Diptera (flies) fossils from Florissant. In 1949, entomologist Axel Leonard Melander described 62 new species of fossil Diptera from Florissant.