| Latah Formation Stratigraphic range: Late Miocene |
|
|---|---|
| Type | Geological formation |
| Underlies | Priest Rapids Member, Wanapum Basalt |
| Overlies | Columbia River Basalt Group |
| Area | 175 miles (282 km) by 75 miles (121 km) |
| Lithology | |
| Primary | Fluvial |
| Location | |
| Named by | Dr. Kirk Bryan |
| Region | Eastern Washington & northwestern Idaho |
| Country | USA |
The Latah Formation is a series of late Miocene lacustrine sedimentary deposits which outcrop in eastern Washington and northwestern Idaho. The lake beds are interbedded with igneous rock of the Columbia River Basalt Group. The formation was originally named from a site in Spokane, Washington by Dr. Kirk Bryan in 1923. Numerous fossil plants and insects have been recovered from the formation and described.[1] When first described the formation was thought to have predated the deposition of the Columbia River Basalts, however further investigation showed them to be coeval.[2]