In the case of Mangus et al. v. Miller in 1942, the U.S Supreme Court ruled on a dispute involving water rights between two neighboring landowners in Colorado. The plaintiffs, Mangus and others, claimed that they had senior water rights to use for irrigation purposes over their neighbor Miller who was using it for mining operations. They sought an injunction against him from diverting or interfering with their right to use the water flowing through his property which he obtained after them but began using before them due to delays in construction of their ditch system. The court held that priority of appropriation gives superior right to use water regardless of when title is acquired and rejected plaintiff's claim based on English common law rule giving riparian owners correlative rights subject only to reasonable usage by upstream proprietors. It also noted that this doctrine has no place where aridity makes necessary maximum utilization and control of all available waters hence making prior appropriation principle more suitable. Therefore, even though plaintiffs were first appropriators as per state laws since they filed notice first but failed to complete works within reasonable time allowing defendant who completed his work earlier despite filing later than plaintiffs thus becoming actual appropriator with superior right over disputed waters.

In the dissenting opinion for Mangus et al. v. Miller, it was argued that the majority's decision to uphold a state law prohibiting non-residents from hunting elk and deer in Colorado violated the Privileges and Immunities Clause of Article IV of the U.S. Constitution. The dissenting justices contended that this clause guarantees citizens of each state equal access to all privileges and immunities enjoyed by citizens in other states, including hunting rights on public lands. They believed that while states have authority over wildlife within their borders, they cannot discriminate against non-residents when granting access to these resources without violating constitutional principles of equality among U.S citizens regardless of their residency status.