Columbia River Basalt Group.

Large-volume lava flows of tholeiitic basalt, basaltic andesite, and subordinate andesite in western Idaho; consists of Imnaha Basalt (17.5-16.5 Ma), Grande Ronde Basalt (16.5-15.6 Ma), Wanapum Basalt (15.6-14.5 Ma), and Saddle Mountains Basalt (14.5-6 Ma). Includes porphyritic basalt and basaltic andesite in western Owyhee County. (Quaternary to Eocene Continental Volcanic and Intrusive Rocks).
State Idaho
Name Columbia River Basalt Group.
Geologic age Miocene
Lithologic constituents
Major
Igneous > Volcanic > Mafic-volcanic > Basaltic-andesite (Flow)
Igneous > Volcanic > Mafic-volcanic > Basalt (Flow)Tholeiitic basalt; Includes porphyritic basalt and basaltic andesite in western Owyhee County.
Minor
Igneous > Volcanic > Mafic-volcanic > Andesite (Flow)Subordinate andesite in western Idaho.
References

Lewis, Reed S., Link, Paul K., Stanford, Loudon R., and Long, Sean P., Geologic Map of Idaho, 2012, Idaho Geological Survey, Geologic Map 9 (M-9); Scale 1:500,000.

NGMDB product
Counties Ada - Adams - Benewah - Boise - Bonner - Clearwater - Gem - Idaho - Kootenai - Latah - Lewis - Nez Perce - Owyhee - Payette - Shoshone - Valley - Washington