All of this isn't to say you couldn't "find a way" to get spendable money out of finding this stash, more so a question of staying on the right side of money laundering and taxation laws while doing so.
Do you have a source for this? My understanding is there is almost no tracking whatsoever of gold. Yes, if you brought in a new poured ingot, someone will want to confirm the purity, but there are no required identification stamps on gold that connect it with an owner (some gold dealer may add them voluntarily). Dealer will be happy to pay cash as long as they know they aren't get scammed.
My father in law buys gold coins all the time. They are all identical and there is no way to determine ownership. You can buy and sell in cash. No questions asked.
Now, if you went to gold dealer and tried to offload $1M worth of unmarked gold ingots, you're risking a call to the police who will ask you where it came from. But beyond that, it's a pretty unregulated market.
Edit: Google "gold scrap refining", it is not an uncommon thing.
You're thinking of the bank account deposit reporting threshold.
"Gold and silver jewelry, like bullion, is also considered a collectible. So if you sell your bullion jewelry for a profit, it is subject to the same maximum 28% capital gains rate for precious metals and must be reported on your income tax return. Current law does not require that dealers report jewelry sales, even when dealing with 22K or 24K bullion-grade pieces, or in quantities above the 25 ounce limits applied to bars and many coins."
If you pay a US person at least $600 in the year, you must report that to the IRS on a Form 1099, usually a 1099-MISC. You don't report individual transactions, you simply report all of the income paid to that person over the course of the tax year. (For foreign persons, the form is the 1042-S, and there is no minimum threshold.)
Like the comment I was replying to, you both are conflating the anti-laundering reporting rules with the IRS income tax reporting rules.