Latah Formation

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 interbedded, being laid down in successive events.[2] Potassium-argon dating of the formation returned an age range of 21.3 to 12.1 million years old, indicating an Early to Middle Miocene age range.[3]

Latah Formation
Stratigraphic range: Early to Middle Miocene
TypeGeological formation
UnderliesPriest Rapids Member, Wanapum Basalt
OverliesColumbia River Basalt Group
Area175 miles (282 km) by 75 miles (121 km)
Lithology
PrimaryFluvial
Location
RegionEastern Washington & northwestern Idaho
CountryUnited States
Type section
Named byKirk Bryan

References
  1. Kirkham, V.; Melville, M. (1929). "The Latah Formation". The Journal of Geology. 37 (5): 483–504. Bibcode:1929JG.....37..483K. doi:10.1086/623639.
  2. Lewis, S. (1969). "Fossil insects of the Latah Formation (Miocene) of Eastern Washington and Northern Idaho". Northwest Science. 43 (3): 99–115.
  3. Gray, J.; Kittleman, L. R. (1967). "Geochronology of the Columbia River Basalt and associated floras of eastern Washington and western Idaho". American Journal of Science. 265 (4): 257–291. Bibcode:1967AmJS..265..257G. doi:10.2475/ajs.265.4.257.


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