[3] The formation reaches a thickness of 230 metres (750 ft),[4] and comprises mudstones, shales and tuff deposited in a lacustrine environment.

[1] During the Early Eocene, the climate of much of northern North America was warm and wet, with mean annual temperatures (MAT) as high as 20 °C (68 °F), mean annual precipitation (MAP) of 100 to 150 centimetres (39 to 59 in), mild frost-free winters (coldest month mean temperature >5 °C (41 °F)), and climatic conditions that supported extensive temperate forest ecosystems.

Using bioclimatic analysis of 45 nearest living relatives, a moist mesothermal climate is indicated (MAT 12.7 to 16.6 °C (54.9 to 61.9 °F); cold month mean temperature (CMMT) 3.5 to 7.9 °C (38.3 to 46.2 °F) and mean annual precipitation (MAP) of 103 to 157 centimetres (41 to 62 in)/yr.

[6] A wide variety of fossils occur in the formation, including abundant fish remains, insects, and plants, and rare occurrences of molluscs, ostracods, and birds:[1] Fossil plants were first reported from the Coldwater Beds at the Quilchena site and nearby by Penhallow (1908)[7] with an expanded taxonomic list given by Mathewes et al (2016).

The invertebrates trace fossils included two undescribed species of Trichoptera larval cases and burrowing or tracks in the sediment.