30 U.S.C. § 49e

During each year and until patent has been issued therefor, at least $100 worth of labor shall be performed or improvements made on, or for the benefit or development of, in accordance with existing law, each mining claim in Alaska heretofore or hereafter located. And the locator or owner of such claim or some other person having knowledge of the facts may also make and file with the said recorder of the district in which the claims shall be situated an affidavit showing the performance of labor or making of improvements to the amount of $100 as aforesaid and specifying the character and extent of such work. Such affidavits shall set forth the following: First, the name or number of the mining claims and where situated; second, the number of days’ work done and the character and value of the improvements placed thereon; third, the date of the performance of such labor and of making improvements; fourth, at whose instance the work was done or the improvements made; fifth, the actual amount paid for work and improvement, and by whom paid when the same was not done by the owner. Such affidavit shall be prima facie evidence of the performance of such work or making of such improvements, but if such affidavits be not filed within the time fixed by this section the burden of proof shall be upon the claimant to establish the performance of such annual work and improvements. And upon failure of the locator or owner of any such claim to comply with the provisions of this section, as to performance of work and improvements, such claim shall become forfeited and open to location by others as if no location of the same had ever been made. The affidavits required may be made before any officer authorized to administer oaths, and the provisions of sections 1621 and 1622 of title 18, are extended to such affidavits. Said affidavits shall be filed not later than ninety days after the close of the year in which such work is performed.