A marker on the outside of the park has this narrative:
Fossil Butte
Fossil Butte is a 50 million year old lakebed and one of the richest fossil resources in the world. It is part of the Green River Formation, a layer of rock composed of laminated limestone, mudstone, and volcanic ash. Complete paleo-ecosystems are preserved in the formation, which is the geologic remnant of the Green River Lake System of the Eocene era. Designated on October 23, 1972, Fossil Butte National Monument encompasses a part of land that was once under Fossil Lake.
Fossil Lake was the smallest and shortest-lived of the Green River System lakes. At its largest size, the lake covered 932 square miles and existed for approximately three million yeas. One phenomenon of the Fossil Lake fossils is their density. There are as many as several hundred fossilized fish per square meter in some portions of Fossil Butte. At least thirteen genera of fish are found in the sediments of fossil lake, as well as a wide variety of species, from large predators like gar and bowfin to the now extinct Knightia, Diplomystus, and Priscacara. Plant and invertebrate records are equally diverse. Evidence of lily pads, horsetails, ferns, palms, and poplar and elm trees exist along Fossil Lake’s floodplain and lower elevations. The remains of dragonflies, mosquito larvae, and water striders bear testament to the vibrancy of this freshwater ecosystem. In addition, evidence of freshwater mollusks, snails, crayfish, and shrimp has been found.
The paleontologist who worked at Fossil Butte have deposited specimens at the Field Museum in Chicago, IL, the American Museum of Natural History, in New York City, and Smithsonian Institution’s National Museum of Natural History in Washington D.C.
Fossil Butte National Monument
Operating Hours & Seasons
Visitors Center Hours:
Summer Season: (May 1 through September 30) 9:00 a.m. to 5:30 p.m.
Fall, Winter and Spring Seasons: (October through April 30)
Weekdays: 8:30 a.m. to 5:00 p.m.
Weekends: 8:00 a.m. to 4:30 p.m.
Monument Visitors Center is closed during all Federal Holidays during the winter months.
Monument grounds are open sunrise to sunset. The entrance road gate is closed only during severe winter storms. The upper road accessing the picnic area, Fossil Lake Trail, and scenic drive closes November 1st until the snow melts, usually by late May.
Phone: (307) 877-4455
History
In 1860, as the Union Pacific Railroad was laying its tracks, a discovery was found just south of the park. As workers dug through the layers of limestone, the discovery of fossils began to emerge. These workers had unearthed fossils in what is called today as the Green River Formation. Over the next century, paleontologists would come to the area, in search of the fossils that were so plentiful in the area.
Today, Fossil Butte National Monument protects only one percent of the entire formation. The monument does provide the public with interpretation of the area, educating people on the science and discoveries related to the area.
Things to do:
- Visit the visitors center. Many examples of actual and cast replica fossils actually discovered in and around the park.
- Take a hike. Two trails are on within the park boundaries. First, a 2 1/2 mile trail to the historic quarry, and a second 1 1/2 mile Fossil Lake trail.