A couple of things.
Getting data related to any dredging operation at that time is exceptionally difficult. That said, I'm working on it. Nonetheless, the photographs themselves tell a story and are compelling evidence that dredge spoils were used to replenish the entirety of Tena Bar in 1970.
Moreover, the photographs also appear to indicate that the dredge spoils placed upon Tena Bar in August 1974 were of a smallish amount and did not reach the money find spot.
Also, Richard Fazio told me yesterday that dredging along this area was done on an as-needed basis. In other words, it wasn't done in a set number of year.
With that in mind, I suspect that I know what happened here.
1) Tena Bar had been allowed to erode appreciably in the late 1960's as evidenced by the July 1968 photos I've displayed.
2) In January 1970 the Columbia River experienced a high water event that crested on January 24, 1970 at only 2 feet below the June 1972 crest.
3) I'm assuming that the January 1970 high water event necessitated a dredging operation later in 1970. And, that it was this dredging operation that accounts for the enormous amount of sand placed upon the entirety of Tena Bar as evidenced by the September 1970 photo I displayed.
4) Then, of course, the next dredge was in August 1974, but on a much smaller scale and did not reach the money find spot.
5) In 1980, the site is excavated by the FBI and Palmer and he incorrectly assumes the dredge spoils he is looking at are from the most recent 1974 dredge, when in reality they're from the 1970 dredge.