Fossil Butte at the edge of Wyoming

Fossil Butte above the ancient shoreline

The full moon stalked me across Wyoming. It emerged from a cloud bank to light the plains, then ducked into multiple patgches of cloud, throwing unexpected light on a highway that should have been pitch-black through Laramie, or maybe the Big Snowy Range. 

From the short mountain pass between Vendauwoo and Laramie, the stony visage of Abraham Lincoln lit the dark mountain pass, a reminder of the road’s Lincoln Highway origins and the high point on Interstate 80 in Wyoming. 

 I saved my stop for Sinclair, the tiny town overlooked by a massive oil refinery. The green Sinclair dinosaur almost seemed to pose in the moments before sunrise. 

 Towns were few after Rawlins. The road crossed the Red Desert to reach the mining town of Rock Springs, then Green River, named for its main waterway, the canyon-cutting tributary of the Colorado River. Only one bore of the Green River Tunnel was open thanks to a fatal car fire in late 2024. 

 Were I not headed further west, Green River’s goal as the gateway to the Flaming Gorge recreation would have drawn my attention. Although the Seedskadee National Wildlife Refuge further north on the Green River, a noted oasis rich in wildlife, might have proven a bigger draw. I stopped briefly at Little America, a resort in western Wyoming. Other than an oasis with gas in a dry country, not much hooked me here. 

After a lifetime of Interstate 80, I sprinted north to Kemmerer, a coal-mining town on few radars these days. Kemmerer is famous due to an unexpected little store on its main street

. John Cash Penney founded a dry goods store in 1902, living above the store initially because he couldn’t afford a separate house. Penney’s store would grow to a chain that occupies downtown retail and shopping malls to this day. I planned to walk the town park, where Penney’s house has been moved. 

Then I locked eyes with the town’s resident homeless man. He didn’t take his gaze off me the entire time I circled the park, heading inexorably in my direction. I knew what reception awaited me the second I stepped away from the car. I could only take a few pictures of the home store, then move on. At least I didn’t have far for the next stop. 

Kemmerer was table-setting for the rare deposit of aquatic fossils just north. Other than signs, few details revealed the significance of Fossil Butte National Monument. Maps don’t always give away the look of monuments. I expected a series of dry hills, not the majestic buttes that formed the shoreline of an ancient lake that thrived in the Eocene Epoch after the extinction of the dinosaurs. 

Recent rain probably made the surroundings appear greener than normal, but the landscape I entered was awe-inspiring. I have visited several fossil beds preserved by the park service, but only Badlands National Park stands as massive as Fossil Butte. 

The ancient lakebed, with water that ran several hundred feet deep, is immediately apparent millions of years after the waters receded. Trails and unpaved roads run deep into the land below the buttes. This lake dwarfed the ancient lake at Florissant Fossil Beds in Colorado. Special conditions always accompany this level of fossil activity. 

The fossilization occurred due to the nature of Fossil Lake 52 million years ago, so everything found here comes after the extinction of the dinosaurs. 

At 60 miles long and 40 miles wide, Fossil Lake had freshwater at its upper reaches and salt water below, with lake mud rich in dissolved limestone that aided fossilization. Dead creatures sunk into the protective mud, and kept away predators. 

 Fish fossils can be rare, but Fossil Butte has an enviable supply of some species. Outside the monument boundaries, private quarries mine for these fossils, with most headed for the collections of private collectors. This monument has plenty of untouched land and new discoveries come with some regularity. 

A broad range of aquatic creatures emerge from the rock. Some are common, but others include giant crocodilians bats, insects, and snails. The fish species include ancient gar, bowfins, herring, perch, paddlefish, and even stingrays. Spiders, millipedes, crayfish, and palm fronds also fell to the mud. The ancestral shores also reveal fossils, including early tapirs and frigate birds. 

The first fish fossil from Fossil Butte was found in the 1850s, and development would move slowly until the 1930s, when more species were dug out for museums and private collectors.

 Quarrying from the 1960s began to probe the fossil trove. In 1972, Wyoming went against its prohibition on new national monuments, when Congress approved national monument protections for Fossil Butte. A half-century later, fossil discovery is ongoing. 

The landscape supports a much hardier ecosystem on these isolated lands. Black-tailed jackrabbits bounded along the road and vanished into the fields of sage below Fossil Butte. Below the buttes, the land waits to give up new discoveries, where unexpected species still lie in the stone.