| The Union Pacific Railroad runs along the south side of the
Columbia River. Basalt flows of the Columbia River Basalt Group crop out
on the Washington side of the river (Allen and others, 1986). The Columbia River Basalt Group preserve a record of massive volcanic floods that inundated thousands of square miles in northern Oregon, eastern Washington and western Idaho during Miocene time, between 17 and 6 million years ago (USGS, 2009). Each of the step-like terraces visible across the river are associated with individual lava flows. |
