Here is the cursory, bloodless opinion in Mound v. United States.
Briefs here. Lower court materials here.
An excerpt:
In 2014, the Tribe identified a culvert—a structure that channels water under a road—as a potential maintenance project. In 2018, based on an engineering assessment, the Tribe decided to replace the culvert. Because its existing contract did not authorize funding for the project, the Tribe sought a new contract with the BIA. Before the new contract was finalized, heavy rains collapsed the culvert, leaving a large gap in the road. Four cars drove into the gap and plunged into the water. Trudy Peterson and James Vander Wal were swept downstream and died. Evan Thompson and Steven Willard suffered serious injuries.
