The Biden administration has decided that contested minerals beneath a portion of the Missouri River belong to the Mandan, Hidatsa and Arikara Nation, and not the state of North Dakota.

The legal opinion from Interior Department solicitor Bob Anderson on Friday backing the Three Affiliated Tribes represents a turn from the Trump administration, which had backed North Dakota's claims to the materials.

“My decision today upholds decades of existing precedent holding that the Missouri riverbed belongs to the Mandan, Hidatsa, and Arikara (MHA) Nation,” Anderson said in a statement. 

“Today’s action, based on extensive historical and legal review, underscores the Department’s commitment to upholding its trust and treaty obligations in accordance with the law,” he added.

This is not the first time the administration has indicated that it would take this approach. Last year it withdrew a Trump-era legal opinion that sided with North Dakota.

But Friday’s action shows the Biden administration is not just withdrawing its support from North Dakota, but is supporting the claims of the Three Affiliated Tribes.

Anderson, in the opinion, cited an 1851 treaty and subsequent executive orders saying that the tribes’ territory surrounded the Missouri River. 

Both MHA Nation and North Dakota have tried to claim rights to the minerals. The Trump-era opinion, which sided with the state, had argued that North Dakota had the mineral rights because of a legal doctrine giving new states that enter the union the same rights as the original 13 states. 

“The original thirteen states maintained possession of submerged lands upon entrance to the Union,” then-solicitor Daniel Jorjani wrote in the now withdrawn opinion.