The United States v. The Widow, Heirs, and Executors of William E. P. Hartnell was a case heard by the Supreme Court in 1859 that dealt with the issue of land grants made to Mexican citizens prior to California becoming part of the United States during the Mexican-American War (1846–48). At issue was whether or not these land grants were valid under US law after California became a state in 1850. The court ultimately held that they were not valid because they had been granted without any legal authority from either Mexico or the US government and thus could not be enforced as contracts between individuals under American law. Furthermore, it found that even if such contracts had been legally authorized at some point before California's admission into union, their validity would have expired upon its admission since all laws passed by Mexico ceased to exist when it ceded control over what is now known as California to America in 1848.

In the United States v. The Widow, Heirs, and Executors of William E. P. Hartnell, Deceased case before the Supreme Court, Justice Grier delivered a dissenting opinion that argued against the majority’s decision to award title to land in California to the United States government rather than its original owner's heirs. Justice Grier believed that Congress had no authority under existing laws or treaties with Mexico to take away private property without just compensation as it did in this case when it granted public lands for military purposes without compensating those who held prior titles from Mexican grants. Furthermore, he argued that if Congress was allowed such power then all other rights would be subject to their discretion and could be taken away at any time without due process of law or fair compensation being provided which is contrary to fundamental principles of justice and equity established by our Constitution. In conclusion, Justice Grier felt strongly that an individual should not have his property taken away from him unless there is clear evidence showing he has forfeited his right through some act on his part or by operation of law; otherwise it violates basic constitutional protections afforded citizens under our system of government