43 U.S.C. § 335 : US Code - Section 335: Further extension in cases not covered by sections 333 and 334 of this title

      The Secretary of the Interior may, in his discretion, extend the
    time within which final proof is required to be submitted upon any
    lawful pending desert-land entry made prior to March 4, 1915, such
    extension not to exceed three years from the date of allowance
    thereof: Provided, That the entryman or his duly qualified assignee
    has, in good faith, complied with the requirements of law as to
    yearly expenditures and proof thereof, and shall show, under rules
    and regulations to be prescribed by the Secretary of the Interior,
    that there is a reasonable prospect that, if the extension is
    granted, he will be able to make the final proof of reclamation,
    irrigation, and cultivation required by law: Provided further, That
    the foregoing shall apply only to cases wherein an extension or
    further extension of time may not properly be allowed under
    sections 333 and 334 of this title or other law existing prior to
    March 4, 1915: Provided further, That in cases where such entries
    have been assigned prior to March 4, 1915, the assignees shall, if
    otherwise qualified, be entitled to the benefit hereof.