Tertiary 

At around the time the dinosaurs became extinct at the end of the Cretaceous, terranes were still accreting to the west. Volcanoes rose to form the Cascade Mountains and spread lava and ash around the province. The demise of the dinosaurs and a drying climate in the Tertiary (65 million to 2 million years ago) left new ecological niches, and mammals, birds and flowering plants rapidly diversified to fill them. West of the Columbia Basin, on the Similkameen River, lived a tillodont, a grazing mammal about the size of a brown bear but of unknown relationship. To the North, near Quesnel, rocks of early Tertiary age yielded a titanothere, a huge herbivore with a prominent hump on the back and a pair of blade-like horns on the end of the snout. And here in the Kootenays, on the banks of the Flathead River, researchers have found fossils of three ancient rodents, an early rabbit, a rabbit-sized, cloven-hoofed deer-like animal, a marsupial in the same family as modern opossum, and a member of the mammal order known as "flying lemurs," although they do not fly and are not lemurs ( McAnally, in Ludvigsen, 1996).