Fossil Butte National Monument

Fifteen miles west of Kemmerer, the ridges of southwest Wyoming hold what the Park Service calls the best paleontological record of Cenozoic aquatic communities in North America, and possibly the world.

The setting was a subtropical freshwater basin. During the Eocene three lakes covered parts of what are now Wyoming, Utah and Colorado: Lake Gosiute, Lake Uinta, and the smallest of them, Fossil Lake. That smallest one is the one that mattered. It ran 40 to 50 miles north to south and about 20 miles across, shifting shape over the two million years it existed, and its bed is the Green River Formation. The monument protects around thirteen square miles of a lake that covered some nine hundred. Hold that ratio in mind: you are looking through a keyhole.

What comes out of it is a whole ecosystem rather than a species list. Fish, alligators, bats, turtles, insects, plants, and a horse the size of a dog. Knightia eocaena is the commonest fossil fish here and Cockerellites liops not far behind, while only two fossil frogs have ever been found in the Fossil Lake sediments. Above the lake beds sits a thick section of the Wasatch Formation, river and stream deposits that record the shoreline instead of the water, carrying teeth and bone fragments from early primates and early horses.

The collecting rule here is the sharpest line in the region, and it deserves precision. Commercial fossil collecting is not allowed inside the national monument. Numerous quarries on private land nearby continue to produce extraordinary specimens for museums and private collectors alike, which is why Kemmerer has a fossil trade at all. The habit is old: coal mining for the railroad settled the nearby town of Fossil, miners dug fossils to sell to collectors, and Lee Craig made a living at it from 1897 until 1937.

In summer, monument staff prepare fossils in public, and a three-quarter-mile hike up the butte reaches the research quarry itself.