I see that you are not familiar with the Tina Bar area. It is not actually developed even today. The search area is relevant only if the flight path is known.
What should any searcher be looking for today? The parachute container and and equipment have a long life expectancy even in salt water. And the two to three pounds of metal in that equipment would survive. Also, Cooper had on a rain coat and the parachute equipment was over it. So it is possible that portions of the rain coat are still contained within the parachute equipment and some of Cooper's bones may well be within that rain coat. If anything from Cooper remains in the Tina Bar area, it is probably buried under sand and probably would have been buried during the 1972 spring flooding.
But don't expect to find any more money. The three packets of money found at Tina Bar were probably still in the damaged money bag when they arrived there. But if the money bag was still attached to Cooper at that point, it has long gone on down stream and so has Cooper.
Where to look? Tina Bar and I have recently explained and posted why here.
Tena Bar is undeveloped? Would that include the very large sand company that completely surrounds it on all sides but for the river? The inner-roads and driveways on their land? How about the massive agricultural plots surrounding that business, or the roads built and telephone wires installed to service that area? I'm looking at Tena Bar right now on Google Maps' satellite view. All those perfect rectangles and parallelograms surrounding it, the road a couple of hundred feet from it, the corn stalks visible on street view, everything looks pretty well-developed and well-traveled to me. Perhaps I lack the ability to adequately interpret what it means when ransom money is found while digging in sand...belonging to the only people on that river for miles who make their living digging in sand.
Tena Bar and its surrounding area have been under close scrutiny since Jimmy Carter was president. There's nothing there. You'll likely find more by digging under the corn field across the street in my opinion.
I'm not unfamiliar with the area surrounding Tena Bar. I was through that area in 2006, the Gorge, all up around Mount St. Helens, all of that sightseeing crap. One of the most desolate drives of my life, that volcano - nothing but trees. Had the worst hot dog and relish of my life on a picnic bench in that area. But what I'm talking about is the potential "reasonable doubt" landing zone. Meaning let's take all reasonable proposals and use them to expand the landing zone, then whittle down a search zone from it.
Now let's talk math. Take the percentage of that enlarged landing zone which is developed. What are the odds that Cooper would splat on developed land and go unnoticed all this time? Let's call it 0% while reserving the right to be off by a rounding error. So subtract all developed land (developed in 1971 or 2020, doesn't matter) from the whole and you have a narrower search area. Also subtract any private property. Nobody is leaving their property untouched for 50 years, and the words, "Fido, what's that you found?" spring to mind.
Next, take all of the places we can say for certain were searched and nothing was found. What are the odds that the authorities and treasure hunters were standing on Coop's shattered, purple torso and didn't smell him? Let's also call it 0% if there was a parachute deployed, 1-5% if not. [Side note: There was a dead deer in the woods along my drive to work last fall. Even with the windows rolled up the smell was overpowering. It lasted a month until I switched routes.] Got a better guess? I'm all ears. Subtract that land area from the remainder above.
What's left over now is a combination of water and land. A lot of what has been written about is Lake Merwin, which cannot feed a spoonful to Tena Bar, so eliminate it, and all of the trickles around it, in the search for a corpse or physical evidence. If Cooper landed in or around Merwin, either he survived and left, or someone took his loot and "disappeared" him, because that money didn't find its way to Tena Bar naturally. So either way, we can cross that area off of the list, too, when searching.
How about the Washougal? Anybody talk to Jerry Thomas lately? Is he still searching out there? If so, he can probably tell us what to eliminate from that area. Also, let's cross off the islands in the river where Nuttall and his buddy searched their hearts out. Plus all of the river area that Tosaw knocked out, et cetera.
What's left is a patchwork of neglected spots in the forest that we can assume - though not safely - have been at least passed through at some point in a half-century, and admittedly pine needles can cover up a lot. Those spots, plus the places on bank of the Columbia that have not significantly been covered, make up our our search zone, which I will bet anything is smaller and with significantly less controversy than any new landing zone created by an alternate flight path. So what percentage of the enlarged landing zone can be eliminated? Probably most of it - by far. Different take on the above? I'm all ears.
I saw you and a team of people on the beach at Tena Bar with metal detectors. I'm not currently convinced of any future significance of Tena Bar to the Cooper investigation, barring the unlikely scenario that the Fazios ended up with the cash. And if that is the only purpose of investigating the flight path further, I would pack it in and say job well done. You've highlighted a very plausible scenario that others had not given much thought to prior. Bravo.
Having said that, anybody have details on what other stretches of the Columbia have been searched/dredged/developed and can be eliminated? Maybe I'll save that for the Tena Bar thread.