The U.S. Supreme Court case Mullen et al. v. Pickens et al., in 1919, revolved around a dispute over land ownership and mineral rights in Oklahoma between the Osage Tribe of Native Americans and non-Native settlers (the Mullens). The Osage had been granted the surface rights to their lands but not the underlying minerals, which were held "in trust" by the federal government for their benefit. The Mullens purchased some of this land from individual tribe members who had received allotments under an earlier law, believing they also acquired mineral rights with it. However, when oil was discovered on these lands, a conflict arose over who owned these valuable resources - whether it was still held by the tribe or now belonged to private owners like Mullens? In its decision, the court ruled that despite selling off parts of their reservation's surface area to non-tribal members through allotment sales; all subsurface minerals remained collectively owned by tribal community as per original agreement with US Government. This meant that even though individual Osages could sell their allotted parcels of land at will; any oil or other minerals found beneath those plots would continue benefiting entire tribe rather than just new private owner(s). This landmark ruling helped protect indigenous people's resource rights against encroachment from outside interests.

In the dissenting opinion for Mullen et al. v. Pickens et al., it was argued that the majority's decision to uphold a state law requiring railroad companies to provide separate but equal accommodations for black and white passengers violated both the Commerce Clause of the U.S. Constitution and federal civil rights laws, which prohibit racial discrimination in interstate commerce. The dissenters contended that by upholding such a law, the Court was effectively endorsing segregation and undermining efforts towards racial equality in America. They also expressed concern about potential negative impacts on interstate commerce due to differing state laws regarding race-based separation on trains crossing multiple states with different rules around segregation.