Fossil Hunting at American Fossil Quarry, Wyoming

American Fossil Quarry is a pay-to-dig site in the Green River Formation near Kemmerer, Lincoln County, Wyoming. The quarry exposes laminated Eocene lake sediments packed with fossil fish, plants, insects, and stingrays dating to roughly 50 million years ago. Visitors split the thin limestone layers themselves and keep every fossil they find.

The quarry sits on private land within the Fossil Lake basin, about 40 minutes north of Kemmerer by a combination of paved highway and dirt roads. Two other commercial quarries, Fossil Lake Safari (formerly Warfield) and Ulrich’s Fossil Gallery, operate nearby in the same formation.

Location and Directions

American Fossil Quarry is about 8 miles north of Highway 233 on Dempsey Road, a dirt county road. The turnoff is roughly 3 miles past the town of Frontier, where a county sign marks Dempsey Road. Follow the dirt road for about 8 miles, crossing four cattle guards onto a plateau. After the last cattle guard, continue about 3 miles until a large white sign marks the left turn to the quarry.

From I-80, take Exit 18 onto Highway 189 north for 36 miles through Diamondville to Kemmerer. Past the center of town, turn right at the Highway 30 junction to stay on Highway 189. After crossing Hamm’s Fork River, turn left at the Highway 233 junction toward Lake Viva Naughton, then follow the Dempsey Road directions above.

The quarry does not have cell service. Download directions before leaving Kemmerer and bring your own water, sunscreen, and food.

What Fossils You’ll Find

The quarry exposes the "split fish layer," a zone of laminated lime muds about 1.8 m (6 ft) thick that formed over roughly 4,000 years of lake-bottom deposition. Fossils split cleanly along the varve layers, which is why the technique works for visitors with no prior experience.

Knightia eocaena is the most common fish at the site. It is a small herring-like species, typically 7 to 10 cm long, that schooled in the upper waters of Fossil Lake. Knightia is so common in these beds that it is described as the most frequently found complete vertebrate fossil in the world, and it is the Wyoming state fossil. A typical afternoon of digging can produce 20 to 35 whole or partial Knightia skeletons.

Diplomystus dentatus is the second most common fish. It is a larger predator, up to 65 cm long, with an upturned jaw that suggests it fed near the surface on schooling Knightia. Diplomystus specimens are less frequent but turn up regularly.

Cockerellites liops (formerly Priscacara liops) is a deep-bodied schooling fish. Mass-mortality layers of Cockerellites suggest whole schools died simultaneously, probably from sudden changes in water chemistry or temperature.

Other fish found at the quarry include Mioplosus labracoides, a predatory perch-like fish that occasionally preserves smaller fish inside its gut, and Phareodus, a large predator with fang-like teeth. Freshwater stingrays of the genus Heliobatis also occur, though they are uncommon.

Plant fossils are found throughout the layer, mainly palm fronds, fern leaves, and leaves from sycamores, willows, and oaks that grew along the lake margin. Insect fossils preserved in the fine-grained limestone sometimes retain wing membrane detail.

On rare occasions the quarries around Kemmerer have produced complete bat skeletons (Icaronycteris), early primates, and even a three-toed horse skeleton. American Fossil’s quarry produced one of only two three-toed horse specimens ever recovered from the formation.

Geologic History

The Green River Formation records the sedimentation of three large intermountain lakes that covered parts of Wyoming, Colorado, and Utah during the early Eocene, roughly 53.5 to 48.5 million years ago. American Fossil Quarry sits in the Fossil Lake basin, the smallest of the three. At its maximum, Fossil Lake was about 50 miles long and 20 miles wide.

The lakes formed in basins created by the Laramide orogeny, the same mountain-building event that raised much of the Rocky Mountains. Sediment washed in from the surrounding highlands, including the Uinta Mountains to the south and the Wind River Range to the north.

The climate in this part of Wyoming during the Eocene was subtropical. Crocodiles, which cannot tolerate frost, lived in the lake. Palms, figs, and cypress grew around the shore, with sycamores, beeches, and oaks on higher ground. Water temperatures supported stingrays, 25 species of fish, and dense stands of aquatic plants.

Fish and other organisms that died near the lake bottom sank into fine calcium carbonate mud. The mud lacked oxygen, which slowed decomposition and kept scavengers away. Layer after layer of carbonate settled over the remains, building up the varved limestone that fossil hunters split today. Each pair of light and dark layers (one varve) records a single year of deposition. The mean thickness of a varve in the Green River Formation is 0.18 mm.

The paleontologist Edward Drinker Cope was one of the first scientists to excavate at Fossil Butte in the 1870s. Commercial quarrying of fossil fish has continued in the area for well over a century. American Fossil operates on private land with exclusive access to its section of the split fish layer.

Collecting Rules and Regulations

American Fossil is a private, fee-based quarry. Collecting is open to anyone who books a session. Visitors keep every fossil they find with no limits.

Dig sessions come in three lengths: 2-hour, 4-hour, and 8-hour blocks. Adult prices (ages 15 and up) range from $89 for a 2-hour dig to $169 for a full 8-hour day. Children ages 6 to 14 pay reduced rates ($59 to $89). Children under 6 are free with a paying adult. A private dig for up to 10 people costs $750. Book through the operator’s website or by phone at (801) 836-7269.

The quarry provides all digging tools. Staff walk visitors through safety, splitting technique, and fossil identification. No prior experience is needed.

The quarry is open seven days a week from 8:00 AM to 5:00 PM (Wednesday hours start at 9:00 AM). Reservations are recommended, especially during the summer season from June through August.

No collecting is allowed on the surrounding BLM land, because vertebrate fossils on federal land are protected under the Paleontological Resources Preservation Act.

Nearby: Fossil Butte National Monument

Fossil Butte National Monument is 9 miles west of Kemmerer on US Highway 30. The visitor center has an extensive display of Green River Formation fossils, including complete fish, birds, bats, and crocodilians. Admission is free. The monument protects an exposure of the same formation but does not allow fossil collecting. Plan to spend an hour or two at the visitor center before or after your quarry dig.

What to Bring

The quarry is remote and has no services. Bring at least 2 liters of water per person, food, and sunscreen. Temperatures on the plateau can exceed 35 C (95 F) in summer with no shade. Wear closed-toe shoes with good traction, a hat, and eye protection.

For packing fossils to take home, bring a Rubbermaid-style bin, thin bubble wrap or foam sheets, and cardboard dividers. Stand the fossil plates on edge, separated by padding. The shale is fragile and breaks easily in transit if plates are stacked flat.

American Fossil Quarry Fossil Hunting Guide