Turtle Cove Member Mural from the Thomas Condon Paleontology Center, painted by Roger Witter.
Seven million years ago rivers chewed down into the soft, ashy soils of large floodplains, carving out river channels and creating lush riparian zones. These riparian woodlands and meadows were the home to grazing ungulates (horses/ camelids) and burrowing mammals (moles, gophers, and ground squirrels). Acidification through time caused a shift from mixed hardwood forests to tall grasslands and semiarid wooded shrub land, similar to what is seen in the current John Day River Valley. Life in the valley was dangerous, with predators about like short faced bears, coyote-like dogs, and multiple species of saber tooth cats.

Life in the Rattlesnake came to an abrupt end seven million years ago as a stratovolcano in the Harney Basin (near current-day Burns) erupted, as pictured in the mural below. Tephra was expelled from the mouth of the volcano, coming down like a fiery hail on the land. The eruption created a pyroclastic flow which attained speeds over 400 mph and spewed hot, ashy gas that reached nearly 1,800 °F. This event cause nearly 13,000 square miles of Eastern Oregon to be covered in an ashy tuff that destroyed everything in its path.

Dominant Fossils Found in this Assemblage:

Vulpes stenognathus (fox) Indarctos oregonensis (bear with long legs, short muzzle) Teleoceras cf. fossiger (grazing rhinoceros. Short legs, barrel chested built like a hippo) Mylohyus longirostris (peccary, pig-like animal) Pliohippus spectans (Single-toed horse, equine ungulate) Amebelodon sp.(genus gomphotheriidae, four tusked elephant relative) Hemiauchenia cf. vera (camel, long neck, looked similar to a llama but with more camelidae features) Machairodus sp. (saber tooth feline, large. Similar in size to living panthers) Bunch grasses