In United States v. Vallejo, the Supreme Court considered a case involving the validity of a Mexican land grant in California. The plaintiff was an American citizen who had purchased part of the land from one of its original grantees and sought to have his title confirmed by the court. The defendant argued that since Mexico had ceded California to the United States in 1848, any prior grants made by Mexico were invalid under U.S law and thus could not be enforced against him as he held title through subsequent purchases from other owners with valid titles recognized by U.S law. In deciding this case, Chief Justice Taney noted that although Congress had passed legislation confirming certain Mexican grants within two years after acquiring California, it did not confirm all such grants; instead it left some unconfirmed but still legally binding on those holding them at that time due to their having been issued before cession occurred and being based upon Spanish or Mexican laws which remained in force until superseded by new laws enacted afterwards for governing these lands now belonging to America's domain . Ultimately, however, Taney found for Vallejo because there was no evidence presented showing that this particular grant fell into either category (i.e., confirmed or unconfirmed) so as to render it enforceable against him despite his later purchase of part of said property from another owner with valid title recognized under US law

In United States v. Vallejo, the Supreme Court was tasked with determining whether a Mexican land grant in California could be confirmed by the United States government. The majority opinion held that Congress had exclusive authority to confirm such grants and that no court of equity or law had jurisdiction over them. Justice Grier dissented from this decision, arguing that it would lead to injustice for those who were granted lands under Mexican rule prior to 1848 when Mexico ceded California to the U.S., as they would not have their rights recognized by either country due to conflicting laws between them. He argued further that if Congress did not recognize these claims then individuals should at least be able to bring suit in a court of equity or law and present evidence of their claim's validity so as not be deprived of their property without due process being observed first.