Plausible. However, that requires Cooper to walk some 8-10 miles with the money before stashing it. It would take him along the western outskirts of Ridgefield (dangerously close to civilization) while still hoarding the money. There are plenty of places along the way for him to stash it, but he decides to wait all the way until he gets to Tena Bar. I would think he would want to stash earlier rather than later.
Quick question ... is there a sign for Tena Bar that is visible from NW Lower River Road? I've seen pictures of the Tena Bar sign that looks to be closer to the shore. But is there a visible marking for it from the road?
If DBC landed in the Carty Unit of the Ridgefield National Wildlife Refuge he can only walk one direction to exit the area and that is east. The railroad tracks border the Carty Unity on its east side. Therefore, DBC would stumble upon the railroad corridor before hitting Ridgefield itself and naturally head south.
Yes, if he landed in the Carty Unit and buried the cash at Tena Bar he would end up walking about 8 miles before stashing the cash. But this makes sense to me. Here's my point:
If I'm DB Cooper descending from the sky along the western edge of Ridgefield and only a few miles south of Woodland under a large white 28' canopy, my immediate concern is going to be, "Did someone see me coming down?"
With this in mind, I would assume that DBC would want to get the hell out of dodge immediately. After all, he doesn't know if the sheriff is about to arrive with dogs in the next 15 minutes.
Therefore, DBC taking the time to bury the cash at his landing spot--which is hard earth and likely not easy-to-dig sand--seems risky because he may get caught, or perhaps he gets away but the authorities with their dogs sniff out the buried cash.
In my mind, it makes more sense to immediately roll with the cash, avoid town, then when he's relatively certain he's free he can make his way to the sandy shores of the Columbia to temporarily stash the cash before walking into town.
And, no, the Tena Bar sign--in fact, no sign referencing the beach--is visible along Lower River Road in that area.