If you've hiked the signed trails on Bayocean you'll have noticed that the ones on the bay side are just off Dike Road, while the ones on the ocean side are not visible from the beach. Rather, they are posted where trees begin. I wondered if that was because they were installed before the south jetty was built and thus could be used to see how much sand accretion could be attributed to them. Since the Tillamook County Parks Department is in charge of trail maintenance, I called Director Del Schleichert to find out.
Del informed me that the signs were placed there in the early 2000s, just before he was hired. He said they were made of a weather-resistant, composite material by workers employed at a state correctional institution, with the date stamped on the back. I confirmed this during a hike on April 8, 2015. They were all stamped either June 2002 or November 2001.
Signs are not placed on the foredunes because the sand is constantly shifting. Thus, any signs installed, or trails built, would require constant maintenance. Tillamook County just doesn't have the budget for that. Bayocean hiking enthusiasts have resolved the problem on their own by placing and maintaining tripods and posts with colored strings to let folks know where they need to leave the beach. Once on the foredune, you can see the trails sign or footprints leading to them. On behalf of those of us who benefit from those tripods, I'd like to thank those who set them up.
As to accretion of sand attributable to the south jetty, that can be seen in aerial photographs and sketches drawn by the Corps of Engineers. Time-lapse photo overlays at Google Earth show very little change since 1994.