Geologic evidence for great quakes...

and tsunamis along the Cascadia subduction zone comes in a variety of forms, one of which is sunken or drowned forests, where stands of living trees were abruptly lowered into the tidal zone during earth movements. Here's a site near Coos Bay, Oregon, visited during an EWU field course (click to enlarge):

And another in Willapa Bay, Washington, where a myriad of tree stumps are exposed during low tide:

While the trees themselves have long died and weathered away, the large stumps still sit in growth position:

Here's a good, but now dated, general article (.pdf format) that describes the work of Brian Atwater and others who have figured out this geologic story.