rved at Fossil Butte. Although fossil fish are the foot-soldiers of the Green River, the formation also yields reptiles such as turtle and crocodiles, and at least one snake. Other fossils show insects, crayfish and freshwater shrimp. It's remarkable to see the fine details of these small, delicate organisms: antennae stretched out for several inches, or the delicate lace of veins in a dragonfly's wings. Leaves of shore-bound plants are also prevalent, especially sycamore trees and fan-palms. Even flying creatures like birds and bats fell into Fossil Lake and were preserved.
Palm trees surrounded Fossil Lake during the Eocene, and dropped in their leaves, where they became fossilized.
The amazing thing about Fossil Butte is this diversity: The Green River Formation preserves an entire ecosystem here. The fish fauna includes 25 species, ranging from small minnows to massive gars, which were 6 feet long and armored in giant diamond-shaped scales. There are even stingrays preserved in the sediments of Fossil Lake, though modern freshwater stingrays are restricted to the Amazon basin in South America. Many of the fish (and other organisms) are concentrated in particularly rich layers that show massive die-offs in the lake community. What caused these die-offs is not known, but is the subject of a short film detailing the work of several paleontologists who do field work at Fossil Butte.
Wandering through the visitor center, I was struck by how complete a community was displayed in the rocks. From the foundations of the food chain to the highest predators, Fossil Butte gives us a unique snapshot of life in the Eocene.
The only snake known from the Green
River Formation is on display in the Fossil Butte National Monument Visitors
"We started it nine years ago, and it's increasing in popularity," says Arvid Aase, a specialist at Fossil Butte. "It's a great experience for them, and it's free." Because it is a national park, visitors cannot keep the fossils they quarry, but the rangers do issue a certificate bearing each sample's museum I.D. number, declaring that the visitor is responsible for contributing it to the collection.
The Green River Formation is not limited to Fossil Butte National Monument, however, which is only 13 square miles in extent. Several local commercial operations work their own exposures of the rock outside the park. For a fee, visitors can not only participate in the quarrying of fossils, but they actually get to keep what they find. Of these commercial quarrying operations, the closest to the park is Ulrich's Fossil Gallery, located just off the park entrance road near Highway 30. Ulrich's program lasts about three hours, and allows the visitor to keep up to 10 fossil fish for a fee of $75. (The state of Wyoming retains any "rare and unusual" fossils: stingrays, gar fish, mammals, birds.) The commercial fossil quarries typically will square off your fossil finds with their rock saws, making them more stable and attractive for display.
Freshwater stingrays are known from Wyoming's Green River Formation, though today this group of fish is only found in South America.
If you don't have enough time to participate in a quarrying expedition,
Ulrich's and other Kemmerer-area rock shops have displays of their fossils
that rival the official display at Fossil Butte. It's worth stopping at
least one shop to check out the variety of petrified critters.
And the area does offer more than just fossils, in case you're caught in the unenviable position of traveling with a nonpaleontologist: The original J.C. Penney store is in Kemmerer, and the local Oyster Ridge Bluegrass Festival entertains music lovers for three days in late July.
I found myself wishing for more time at Fossil Butte. On the return leg of my roadtrip, my schedule was focused on getting back to the comforts of home, but Fossil Butte has a special magnetism to it. Having stopped there and sampled the wealth of fossils, I found myself craving more. Were I to do it over again, I would schedule several days in the Kemmerer area. This is not merely the acq