Klondike Mountain Formation
| Klondike Mountain Formation Stratigraphic range: Ypresian, 53.5–48.5 Ma |
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Klondike Mountain Formation outcrop at site A0307
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| Type | Geological formation |
| Unit of | Okanagan highlands |
| Sub-units | Tom Thumb Tuff, Lower Member, Upper Member |
| Underlies | Glacial deposits |
| Overlies | Sanpoil Volcanics & others |
| Thickness | up to 3,200 ft (980 m) |
| Lithology | |
| Primary | varied |
| Other | see text |
| Location | |
| Region | Okanagan highlands |
| Country | United States |
| Type section | |
| Named for | Klondike Mountain |
| Named by | Muessig |
| Year defined | 1962 |
The Klondike Mountain Formation is an early Eocenegeological formation located in the northeast central area of Washington State. The formation, named for the type location designated in 1962, Klondike Mountain north of Republic, Washington, is composed of volcanic rocks in the upper unit and volcanics plus lacustrine (lakebed) sedimentation in which a lagerstätte with exceptionally well-preserved plant and insect fossils has been found, along with fossil epithermal hot springs.
The formation is the youngest in a group of formations which belong to the Challis Sequence rocks. The formation unconformably overlies rocks of the Eocene Sanpoil Volcanics and much older Triassic and Permian formations. The formation is bounded on its edges by a series of high-angle strike slip faults, which have contained the Klondike Mountain Formation in a series of graben structures, such as the Republic Graben.
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. The town of Republic, Washington is situated at the southern end of the formation, with outcrops within the city itself. The Curlew basin is situated north of Republic, with the northern edge along the Kettle River and the community of Curlew, Washington near the northeastern edge.
The formation is the southernmost of a string of preserved Eocene highland lakebeds in Washington state and British Columbia. The lake system, within the Okanagan highlands, extends from the Klondike Mountain Formation north approximately 1,000 kilometres (1,000,000 m) in to southern central British Columbia.
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