Public access to a fossiliferous outcrop at the north end of Republic is mediated by the nonprofit Stonerose Interpretive Center.

The formation is located in northern Ferry County, Washington, with the majority of the sedimentation in the Republic and Curlew Basins on the east and in the Toroda Creek area to the north west.

[4] The lake system, overlapping the modern Okanagan highlands, extends from the Klondike Mountain Formation northwest approximately 1,000 kilometres (1,000,000 m) in to central British Columbia.

[7] This date was based in examination of fossils by C. R. Eastman, who thought them to be similar to those found in the Florissant Formation of Colorado, which at the time was also considered Miocene.

[11] Since then the fossil-bearing strata of the Formation have been radiometrically dated, to give an estimate of the Ypresian, the mid stage of the early Eocene,49.4 ± .5 million years ago,[5] which was revised to an oldest age estimate of 51.2 ± 0.1 million years ago which given based on detrital zircon isotopic data published in 2021.

[14] In general the lower portions of the Formation have a large amount of hydrothermal alteration, and areas around vents are rich in pyrite and silica.

[15] The lake bed sediments preserve a diverse array of plants, insects, and fishes, notably the biota called the Republic flora.

[17] The area likely had a mesic upper microthermal to lower mesothermal climate, in which winter temperatures rarely dropped low enough for snow, and which were seasonably equitable.