Eocene Fossils of the Okanagan Highlandsby Wes Wehr. The Burke Museum, University of Washington. Vancouver Island Paleontological Society Newsletter, March 1993.
The Okanagan Highlands of British Columbia and Washington State contain some of the most important fossil plant, insect and fish localities in North America. Fossil sites of Princeton, Smithers, McAbee, Horsefly, Chu Chua and Quilchena in British Columbia, and at Republic in Washington State, have produced the World’s oldest fossil specimens of blackberry, serviceberry, apple, wild currant, rhododendron, madrona, spruce, hemlock and true fir, to name a few. Why are these fossils, dated at 48-49 millions years old, found only in the Okanagan Highlands and several localities of the same age north of Princeton? Why are they found only there and nowhere else in the world? The answer is a startling one: The Okanagan Highlands, and upland areas ranging north to Horsefly and Smithers, were then at a significantly higher altitude than any other known area in the world. How do we arrive at such a dramatic claim? By a careful comparison of all the fossil plant sites known world wide from that same geological time. Based upon the fossil plants found at each Middle Eocene locality — in England, Europe, Australia, Asia, North and South America — we can describe what the forests and general vegetation were like in each area at that time. With the exception of a very important Eocene fossil site at Axel Heiberg Island in the Canadian Arctic, presently being studied by Dr. James F. Basinger at the University of Saskatchewan, the British Columbia-Washington State middle Eocene forests were unlike any others known from that time. They contained the earliest known fossil records of warm _ temperate forests as we know them today, as opposed to the tropical vegetation abounding elsewhere. The other fossil forests from that time are clearly typical of lowland vegetation and considerably warmer climates. These lower altitude forests were dominated (as we can see in the Eocene fossil—bearing localities near Bellingham, Washington) by palm trees, species of ferns which grow in Central America, and members of similarly warmer—climate tree families such as the laurel and magnolia families.
Why is there such a dramatic difference between the coastal lowland forests and the upland mountainous forests in British Columbia nearly 50 million years ago? The answer then is much the same as it is today: the higher the altitude, the cooler the temperature. If that is the case, then why, you may well ask, do we find some very "tropical" trees and shrubs growing in the mountainous forests of Princeton, the other inland British Columbia upland localities, and Republic at that time? Why do we find laurel family plants such as Phoebe, now found in tropical forests — or members of the mahogany, citrus, and sandalwood families? These are hardly the sort of trees which one would expect to find today growing naturally in a typical Northwest conifer forest. They’re relics from lowland forests, plants that briefly survived the uplift of the mountains during the middle Eocene in Western North America. They are plants that somehow managed to adapt for a while to increasingly higher altitudes and progressively cooler mountainous climates, to be finally replaced by trees and shrubs which could thrive in such a new environment.
Images can be found at Washington Geology, Vol 20, pp20.