Eocene Okanagan Highlands

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 majority of the paleolake deposits are compression fossils in lake bed sediments spanning a 1,000 km (620 mi) transect,[1] which have been grouped informally into "Northern", "Central", and "Southern" sites.

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.

[7] These expeditions resulted in a series of papers on the plants, authored by John William Dawson, later David Pearce Penhallow and Edward Wilber Berry.

[8] While reporting on additional plant fossils collected from British Columbia, Penhallow (1906) noted the likely coeval status of the Princeton basins with many of the sites now considered the Okanagan Highlands.

[10][11] Republic, Washington, area fossils were first reported by Joseph Umpleby (1910), based on fish he collected near the Tom Thumb mine, and given a tentative late Miocene age.

[12] Two of the fish were figured and briefly mentioned 7 years later by Charles R. Eastman, who assigned them tentatively to "Amyzon" brevipinne, making one of the early connections between Republic and the British Columbian sites.

[17] The term "Okanagan Highlands" for Eocene formations of the region was coined by Wesley Wehr and Howard Schorn in a 1992 Washington Geology paper on the conifer research at Republic.

The highlands temperate biome, preserved across a large transect of lakes, recorded many of the earliest appearances of modern genera, while also documenting the last stands of ancient lines.

[1] The majority of formations in the Eocene Okanagan Highlands preserve compression fossils in sandstone to shale rock deposited from lake environments where seasonal mixing and anoxia were prevalent.

[23] The warm temperate uplands floras of the highlands, associated with downfaulted lacustrine basins and active volcanism are noted to have no exact modern equivalents, due to the more seasonally equitable conditions of the Early Eocene.