Eocene Okanagan Highlands
The Eocene Okanagan Highlands or Eocene Okanogan Highlands are a series of Early Eocene geological formations which span a transect of British Columbia, Canada, and Washington state, United States. Known for a highly diverse and detailed plant and animal paleobiota the paleolake beds as a whole are considered one of the great Canadian Lagerstätten. The paleobiota represented are of an upland subtropical to temperate ecosystem series immediately after the Paleocene–Eocene thermal maximum, and before the increased cooling of the middle and late Eocene to Oligocene. The fossiliferous deposits of the region were noted as early as 1873, with small amounts of systematic work happening in the 1870–1920s on British Columbian sites, and 1920–1930s for Washington sites. Focus and more detailed descriptive work on the Okanagan Highland sites started in the late 1960s. Extent The majority of the paleolake deposits are compression fossils in lake bed sediments spanning a transect, which have been grouped informally into "Northern", "Central", and "Southern" sites. The Northern sites are composed of unnamed Ootsa Group formations which outcrop as the "Driftwood shales" near Smithers, British Columbia, and the "Horsefly shales", of an unnamed formation and unnamed group which outcrop around Horsefly, British Columbia. The Central sites represent Kamloops Group formations with the McAbee Fossil Beds, Tranquille River site and Falkland site, all in the Tranquille Formation, the Quichena site and Stump Lake site in the Coldwater Beds and outcrops of the Chu Chua Formation near Barriere, British Columbia. The Southern sites include the Princeton Group Allenby Formation sites surrounding Princeton, British Columbia, such as "Nine Mile Creek", "One Mile Creek", "Pleasant Valley", "Thomas Ranch", "Vermilian Bluffs", and "Whipsaw Creek". The most southerly of the Okanagan Highlands lakes, the Klondike Mountain Formation in Northern Ferry County, Washington, include the "Boot Hill site", "Corner Lot site", "Gold Mountain site", "Knob Hill site", and "Mount Elizabeth site". Closely correlated with the Klondike Mountain Formation are the Penticton groups Kettle River, Marama and Marron Formations in the Boundary District along the Canada–United States border. There is debate as to the affiliation of the, now lost, Quesnel sites with the Greater Okanagan Highlands. Archibald et al (2018) in the monograph overview of the Highlands Hymenoptera included them as part of the series. However the certainty for the placement was later questioned by Archibald and Cannings (2022) who opted to tentatively exclude Quesnel from the highlands while discussing the history of field collecting in the region. History The earliest geological work in south and central British Columbian sites was during exploratory expeditions under the leadership of George Mercer Dawson in the mid-1870s to document the coal and mineral resources of British Columbia. During the 1875 field work, fossil collections were made in the Quesnel region. Two years later, in 1877, the expedition explored the Okanagan, Nicola, and North Thompson valleys with field collecting along areas of the Similkameen River, Whipsaw Creek and Nine-Mile Creek, north at around Quilchena, and at several areas near Kamloops. These expeditions resulted in a series of papers