Basalt and basaltic andesite

Flows, flow breccia, and pyroclastic deposits. Flows are aphanitic to finely crystalline, commonly diktytaxitic, and aphyric to porphyritic. Textures are mostly intergranular grading to intersertal; some andesite flows are finely trachytic and a few basalt flows are subophitic. Phenocrysts, mostly unaltered, include bytownite and labradorite, olivine, calcic augite, and hypersthene. Flows and breccia form shields, lava cones, and valley fill; in places greatly dissected and modified by fluvial erosion. Includes Boring Lava of Trimble (1963) and Hampton (1972) and Battle Ax Basalts of Thayer (1936). Potassium-argon ages from this unit range from about 1.2 to 3.9 Ma; in places difficult to distinguish from youngest flows of unit Trb
State Oregon
Name Basalt and basaltic andesite
Geologic age Pliocene to Pleistocene
Lithologic constituents
Igneous > Volcanic > Mafic-volcanic > Basalt (Pyroclastic, Flow, Volcaniclastic-volcanic breccia)
Igneous > Volcanic > Mafic-volcanic > Basaltic-andesite (Pyroclastic, Flow, Volcaniclastic-volcanic breccia)
NGMDB product
Counties Clackamas - Crook - Deschutes - Douglas - Harney - Hood River - Jackson - Jefferson - Klamath - Lake - Lane - Linn - Malheur - Marion - Multnomah - Wasco - Washington