Heh... the bursting of ice dams holding back inland glacial meltwater lakes (at least two such events have been documented) could have raised world sealevel in fairly short order, since the thaw was going on all over the place simultaneously. (’:
That’s possible, but don’t forget that Oregon lies along the “Ring of Fire”; I think tectonism is probably the more likely candidate here, given the proposed dates of the ghost-forest.