in 1885 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 on the plants, authored by
John William Dawson, later
David Pearce Penhallow and
Edward Wilber Berry. The insects were first detailed by
Samuel Hubbard Scudder, with follow-up papers by
Anton Handlirsch. 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. The first brief work on fish from the Highlands occurred with the 1893 report by
Edward Drinker Cope on several fish sent to him by George Dawson from the Tranquille and Princeton areas. While Cope deemed the Tranquille specimens too incomplete to identify, he did provide the description for
"Amyzon" brevipinne from the Similkameen River fossils. in 1998
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. 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. Report of the plant fossils of the Republic area were first published by Berry (1929) who included the Republic fossils as part of the
Latah Formation. The inclusion within an expanded Latah Formation was questioned by
Roland W. Brown in 1936, who noted the similarities between Republic and other older fossil sites, combined with the Republic lake bed's overlying basalts then thought to be of similar age to the
Columbia River Basalts. This similarity was again noted by
Chester A. Arnold during his review of the conifer flora associated with the Princeton basin. Arnold noted the Allenby sites shared over half of the taxa that had been previously reported from Republic. Starting in the early 1960s and extending through the 1980s were a series of papers on the British Columbian sites combining palynology and the newly devised process of
potassium–argon dating to better understand the geochronology of the sites. 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 name was derived from the current
Okanagan Highlands but applied to the, as then identified,
microthermal forests preserved at Republic and Princeton. The term was expanded upon, and by 2005 it was generally understood to encompass all Eocene fossiliferous formations between Republic and
Smithers, British Columbia. The highlands as a whole have been described as one of the "Great Canadian
Lagerstätten" ==Preservation types==