In the 1972 case of Mattz v. Arnett, Director, Department of Fish and Game, the U.S. Supreme Court ruled in favor of Raymond Mattz who was a member of an Indian tribe that had signed a treaty with the federal government in 1864. The issue at hand was whether or not land reserved for tribal fishing rights by this treaty remained as such despite being opened to settlement under subsequent legislation. The State of California arrested Mattz for gill net fishing on these lands without a state license which he argued violated his tribal rights under the treaty. The court held that Congress did not intend to terminate reservation status when it passed laws opening up reservation lands for settlement; thus, they were still considered "Indian country" where state law does not apply unless Congress expressly provides otherwise. Therefore, California's application and enforcement of its fishery conservation laws within these areas were deemed invalid because they infringed upon federally protected tribal rights.

In the dissenting opinion for Mattz v. Arnett, Justice Blackmun argued that the majority's interpretation of the 1864 Act was incorrect and overly broad. He contended that Congress did not intend to create a reservation with this legislation but rather sought to protect tribal fishing rights within specified boundaries. The language used in the Act, according to him, does not explicitly establish a reservation but merely defines an area where Indians could fish without interference from non-Indians. Furthermore, he pointed out that subsequent actions by both federal and state governments have consistently treated these lands as public domain rather than reserved territory. Therefore, he believed it was inappropriate for the Court to reinterpret historical events and legislative intent based on current perspectives or desires.