Bayocean Spit Breached in 1700

When a winter storm ripped a 3/4 mile wide gap between Cape Meares and Bayocean Spit on November 13, 1952, the sand covered oyster beds in Tillamook Bay. Over the decades that followed, research confirmed the residents' belief that construction of the north jetty at the entrance of Tillamook Bay, without a south jetty to match, caused the destruction of the spit and its resort town. What no one realized then was that this larger breaches had happened long before jetties were ever considered. 

Figure 10, page 467, Journal of Geology, July 2004

In "Sediment Accumulation in Tillamook Bay, Oregon: Natural Processes versus Human Impacts" (Journal of Geology; July 2004), Oregon State University oceanographers Paul D. Komar, James McManus, and Michael Styllas (whose 2001 master's thesis provided the data) conclude that the Bayocean Spit was breached many times - and to a much greater extent than in 1952 - following the last major Cascadia subduction zone earthquake in January 26, 1700. Figure 10 on the right makes the point graphically.

Studying Tillamook Bay core samples, the researchers found several layers of ocean sand (differentiated from layers of river sediment) in the century and a half after the 1700 earthquake, most of which were larger than the layer attributed to the years 1952 to 1956 (when the gap was closed). They knew from the research of others that fault movement accompanying the 1700 earthquake had lowered the elevation of Bayocean by a meter. This then made it possible for severe winter storms to breach the lower-elevation southern end of the Bayocean Spit. The breaches ceased, and the spit reconstituted by natural processes, prior to the arrival of white settlers. 

This surely was an event the Tillamooks would have experienced and passed down as legend. Though I've not found one in books on the subject, Mack Rhoades tells it on Garibaldi Oregon Memories:

I used to love sitting around the campfire and hearing the tale of 'Thunderfish' being told by a Native American local. Seems that tribes from the South came up to drive away the People's of the Tillamook... when they called upon Thunderbird to save them. Thunderbird flew far to sea and spoke to Thunderfish, who raised his mighty tail high above the water as Thunderbird flew back to tell the People's of the Tillamook to flee to the highest mountains. Then the mighty Thunderfish slapped his tail upon the waters, shaking the very land itself and sending a wall of water over the lands, drowning the invaders from the South and cleansing the land of their existence. Then the People's of the Tillamook returned, making sacrificial offerings of the survivors from the South to both Thunderfish and Thunderbird for their great help... the People's of Tillamook lived for many moons in peace until the great fish with white wings brought the White men to their lands....and the rest we all know, is history!

Legends from other tribes are told at Native American Legends of Tsunamis in the Pacific Northwest. In "The Really Big One" (The New Yorker; July 20, 2015) Kathryn Schulz includes similar legends, and then notes: "It does not speak well of European-Americans that such stories counted as evidence for a proposition only after that proposition had been proved." It is indeed hard to imagine T.B. Potter asking Tillamooks what they thought of his plans for Bayocean Park.