Fossil Butte National Monument

Summer (June through August) is the finest season — the visitor center is fully staffed, the fossil preparation lab is active (with paleontologists working on current-season excavations — visitors can observe and ask questions), the full trail network is accessible, and the monument’s interpretive programs are at their richest. The high-desert plateau is warm (75–85°F) in summer with cool nights; afternoon thunderstorms can occur but are typically brief. Spring (May and early June) and fall (September through October) are pleasant and less crowded but the visitor center staff and programs may be reduced. The monument is open year-round; winter brings snow to the plateau and the trails may be impassable, but the visitor center (if open) offers an exceptional fossil museum experience regardless of season. Summer for the full interpretive experience is the clear recommendation.

The Green River Formation fossils at Fossil Butte were first scientifically documented in the 1870s by paleontologists associated with the Hayden and King geological surveys of the American West; the staggering quality and diversity of the fish fossils immediately attracted scientific attention and, soon after, commercial fossil collectors. Commercial fossil quarrying at Fossil Butte operated from the 1890s through the mid-20th century; the area was a significant source of fossil fish for museum collections worldwide. The national monument was established in 1972 to protect the scientific integrity of the fossil deposit from continued commercial extraction (private fossil quarrying continues legally on private and state land adjacent to the monument — several private quarries offer fee-based fossil digging experiences for visitors, which are entirely separate from and adjacent to the monument). The monument’s paleontological research program has produced significant scientific contributions to the understanding of Eocene ecosystems.

The Green River Formation at Fossil Butte is a sequence of finely laminated lacustrine (lake) limestone and oil shale deposited in the ancient Fossil Lake — a subtropical freshwater lake that occupied portions of the Bridger Basin of southwestern Wyoming approximately 52 million years ago during the Eocene epoch. The limestone layers are varved (alternating light and dark layers deposited seasonally), with each varve couplet representing one year of deposition; the extreme fine grain size of the lacustrine limestone created the extraordinary preservation conditions. Fish and other organisms that died in the lake settled to the anoxic bottom (the deep lake bottom lacked oxygen, preventing the scavenging and bacterial decomposition that would destroy soft tissues) and were slowly buried in the accumulating limestone, preserving them in remarkable three-dimensional detail. The Green River Formation is also famous for its oil shale (kerogen-rich layers that could theoretically be exploited as an unconventional petroleum resource) and covers a vast area of Wyoming, Colorado, and Utah.

Fossil Butte National Monument’s high-desert plateau and sagebrush-grassland habitat support a characteristic Wyoming high-desert wildlife community. Pronghorn antelope (North America’s fastest land animal; abundant on the sage flats around the monument) are frequently visible from the monument roads and trails. Mule deer browse the sparse shrublands. Prairie dogs (white-tailed prairie dog; the high-elevation species) inhabit the monument flats. Ferruginous hawks, golden eagles, prairie falcons, and red-tailed hawks hunt over the open country. Sage grouse (the iconic and conservation-sensitive bird of the Wyoming sagebrush) display in their leks (breeding grounds) on the plateau in early spring. Horned larks, western meadowlarks, sage sparrows, and Brewer’s sparrows are the dominant songbirds of the open country. Badgers and coyotes are the primary predators of the prairie-dog community.

Fossil Butte National Monument’s high-desert sagebrush ecosystem is one of Wyoming’s most intact big-sagebrush steppe communities — the Wyoming big sagebrush (“sage” properly refers to Artemisia tridentata, the silvery, aromatic shrub that is the defining plant of the Great Basin and Wyoming intermontane basins) covers the plateau and slopes around the monument in dense, unbroken stands that support the full suite of sagebrush-obligate wildlife (greater sage grouse, sage sparrow, Brewer’s sparrow, sagebrush vole, and pygmy rabbit). The monument’s management focus is on protecting the fossil-bearing strata from erosion, unauthorized collecting, and trampling — visitors must stay on designated trails to prevent disturbing the fossil-rich surface exposures.

Fossil Butte National Monument holds a unique and important place in the world of paleontology — the Green River Formation fish fossils are among the most scientifically significant and aesthetically extraordinary vertebrate fossils known, and Fossil Butte is the monument dedicated to their preservation and interpretation. For Wyoming, the monument is a point of genuine scientific pride; for the global paleontological community, the Green River Formation of the Kemmerer area is one of the defining sites in the history of vertebrate paleontology. The opportunity to observe active fossil preparation by NPS paleontologists — to watch a 52-million-year-old fish emerge from its limestone matrix in real time — is one of the most distinctive interpretive experiences in the National Park System.

Fossil Butte National Monument is approximately 11 miles west of Kemmerer, Wyoming, via US-30 west then north on WY-412 to the monument entrance. Kemmerer (the nearest full-service town, famous as the site of James Cash Penney’s first Golden Rule store in 1902) is about 100 miles northeast of Salt Lake City, Utah, via I-15 north and US-30 east. The monument visitor center is on the north side of the Commissary Ridge plateau; the entrance road (paved) leads to the visitor center parking area. No entrance fee for the monument. Summer hours for the visitor center are typically 8 AM–4:30 PM; check NPS for current hours (reduced in shoulder seasons). Check NPS for current trail conditions, visitor center hours, and fossil preparation lab schedule before visiting.

The National Park Service manages Fossil Butte National Monument. The fossil-bearing Green River Formation strata are the monument’s most critical resource; it is a federal crime to collect any fossil material (including any fragment of fossil-bearing limestone, any fish scale, any impression or cast) from the monument. The fossil exposures on the monument’s slopes are fragile — stay on designated trails at all times; off-trail travel compacts and damages the fossil-bearing surface exposures. Report any unauthorized fossil collecting to the monument staff. If you wish to dig for fossils, several private quarries on adjacent private land (notably Ulrich’s Fossil Gallery and others near Kemmerer) offer legal fee-based fossil digging experiences. Support the monument’s interpretive and scientific programs.

Fossil Butte National Monument’s trails traverse high-desert badlands terrain (steep, loose, and eroded slopes of limestone and shale) that can be slippery when wet; wear appropriate footwear and stay on designated trails. The high plateau (approximately 7,000 feet elevation) experiences afternoon thunderstorms in summer; be off exposed ridges by early afternoon. Summer heat on the exposed limestone and shale slopes can be intense (85–95°F in direct sun at midday); carry 2+ liters of water per person and start hikes in the morning. The monument is remote — no cell service; carry a first-aid kit and a paper map. Rattlesnakes (prairie rattlesnake) are present in the monument in summer; watch where you step and place your hands.

No entrance fee for the monument. No fossil collecting of any kind (federal law; all fossil material in the monument is protected). Stay on designated trails. No off-road vehicle use. Pets on leash; not recommended on the more rugged trails. No camping in the monument; camping is available at Kemmerer city campground and nearby BLM land. Pack out all trash. Check NPS for current visitor center hours, trail conditions, and any special program schedules before visiting. For legal fossil digging, visit private commercial quarries adjacent to the monument (Ulrich’s Fossil Gallery and others — inquire in Kemmerer for current options).

Kemmerer, Wyoming (11 miles east — the historic coal-mining and fossil-fishing town, home to the first J.C. Penney store — “The Mother Store” — still operating at its original 1902 location; full services for a small Wyoming town), the Hams Fork River (excellent trout fishing in the Bridger-Teton National Forest to the north and east), Flaming Gorge National Recreation Area (100 miles south via US-191 — extraordinary red-rock canyon scenery on the Green River, with exceptional trout fishing and boating), the Star Valley of western Wyoming (to the northwest via WY-89 — a beautiful agricultural valley with Swiss-inspired character and excellent services), and Salt Lake City (100 miles southwest via I-15) define the region. Fossil Butte is the essential destination for any visitor interested in paleontology traveling through southwestern Wyoming.

Visit the fossil preparation lab in the visitor center first thing in the morning (the paleontologists typically begin work early and are most communicative before the midday visitor rush); the experience of watching a 52-million-year-old Knightia fish emerge from its limestone matrix is something visitors consistently describe as the most memorable moment of their visit. After the visitor center, hike the Historic Quarry Trail (the longer option — approximately 4 miles round trip) through the color-banded badlands to the 1920s fossil quarrying site for the full geological and historical context. If you wish to dig your own fossils legally, call ahead to one of the private quarries adjacent to the monument in Kemmerer and reserve a digging session; most visitors successfully excavate and keep one or more fossil fish specimens, which provides an unforgettable paleontological souvenir.