I am outside my usual squares here, so take this as a starting point rather than a figure. The Columbia is the outer limit: the river is tidal well upstream, as far as Bonneville Dam, so no ocean surge could run farther than that. How far a Cascadia tsunami actually travels up the river depends on wave height, the tide at the time, river flow and the shape of the channel, and that is what the state inundation models try to work out. Oregon DOGAMI’s tsunami inundation maps are the place to start for the lower river.
