The St Johns dump theory,
I had a dump float TBAR theory a while back so I'll document it here. It is pure speculation.. based on some assumptions.
Cooper survived the jump with the money,
Cooper was a local resident,
The money was deposited on TBAR intact,
The money was deposited years after the hijack,
The money travelled a short distance and had little water exposure.
The theory is that the money floated to TBAR from the St Johns dump inside some type of bag, wrapping or containment, about 6 easy miles to TBAR. The dump is a vector that can put Cooper anywhere from Albany to Tacoma.
The dump is in the slough surrounded by water, it drew garbage from as far away as Tacoma. There are reports of illegal dumping by people and contractors all around the dump area. The place was a huge mess completely surrounded by water that flowed into the Willamette just before the Columbia.
The theory,
Cooper survived the jump with the money, hid the money at his residence, inside a wall, attic or object, maybe in a garage or barn. Two scenarios,,
Some of the hidden money was found by a relative and thrown in the garbage, not knowing what it was they thought it was trash. It ended up at the St Johns dump.
OR
Cooper suddenly lost control of the residence and money, he possibly died or went to prison. The residence was sold/demolished and the debris taken to the St Johns dump. If so, the rest of the money may be in that dump.
If you research the St Johns dump/landfill, you can get a sense of the place in the 70s..
I have attached a Google Earth .kmz file in zip form flyover that shows the float path from the dump to TBAR.. hope it works,