25 U.S.C. § 5104

For the purpose of effecting land consolidations between Indians and non-Indians within the reservation, the Secretary of the Interior is authorized, under such rules and regulations as he may prescribe, to acquire through purchase, exchange, or relinquishment, any interest in lands, water rights, or surface rights to lands within said reservation. Exchanges of lands hereunder shall be made on the basis of equal value and the value of improvements on lands to be relinquished to the Indians or by Indians to non-Indians shall be given due consideration and allowance made therefor in the valuation of lieu lands. This section shall apply to tribal, trust, or otherwise restricted Indian allotments whether the allottee be living or deceased.