Above the striking blue-green beds of the Turtle Cove are the buff-to-pink volcanic sediments of the 25-24 million year old Kimberly and the fluvial sandstones and conglomerates of Haystack Valley. With similar flora and fauna, the two youngest assemblages of the John Day Formation (Kimberly and Haystack) are commonly grouped together. Most recently, Haystack Valley is broken up into four members: Haystack Valley, Balm Creek, Johnson Canyon, and Rose Creek.
Many taxa persist from Turtle Cove into the upper John Day, but the overall fauna suggests more open habitats. The habitat was forest and field, with elm, birch, oak, maple, fir, spruce, and smaller plants and shrubs. Grasses start to appear and the most abundant mammals from the Kimberly fauna are gophers. Burrowing beavers, another specialized tooth-digging animal, which would have preferred open habitats, are common as well. Greater abundance of running adapted herbivores, like camels and ‘stilt-legged’ horses, and the presence of Daphoenodon, the first running adapted predator in Oregon, support the interpretation of more open environments at this time.
In general, the climate became cooler and drier. The appearance of bunch grasslands and the spread of sagebrush steppe occurred at the expense of forests, woodlands, and swamps, which had previously dominated the area. Ecosystems changing to more open habitats correspond with the appearance of burrowing and running animals. Paleosol (fossilized soil) evidence indicates that the ecosystems continued to evolve, with short sod grasslands appearing by the end of the Upper John Day assemblage.