If you're going to "cash out" after finding millions of dollars in rare gold coins in your cornfield - and don't enjoy looking over your shoulder for 3-letter agents - then it might be useful to get a professional archaeologist's "stamp of historical authenticity" for your find.
https://www.npr.org/2022/06/13/1104823285/treasure-hunters-f...
> Found property. If you find and keep property that doesn’t belong to you that has been lost or abandoned (treasure trove), it’s taxable to you at its fair market value in the first year it’s your undisputed possession
P. 73 [https://www.irs.gov/pub/irs-pdf/p17.pdf]
As someone who loves to just collect coins I'd be really sad to depart with any.
Is it "Found property"? The (unnamed) current owner didn't find the gold coins floating down the river, nor sitting by the side of the road - they were buried on land that he owned. IANAL - but I suspect that there are very clear laws about stuff that you leave behind when you sell a piece of property. If only because the alternative would be a legal nightmare.