I have a letter from the GSA Governmental Services Administration, they oversee all the assets of the United States. They have a form for you to fill out identifying where on US property the treasure is located. Then you can get permission to recover a treasure at your own expense. You have to be protective of any historical artifacts and as far as hard specie or bullion the government retains and the discover after all expenses gets 50% of the value of the treasure. It does not sound like a bad deal to me at all.
If the treasure is on private property then you have to secure written permission to dig and recover the treasure. The same rule applies as above once the treasure is recovered except now you have to split your 50% with the landowners.