In Pico v. United States, the Supreme Court was asked to determine whether a land grant made by Mexico before it ceded California to the U.S. was valid under American law. The case involved a large tract of land in Southern California that had been granted by Mexican authorities to Andrés and Pío Pico in 1845, two years before the Treaty of Guadalupe Hidalgo ended the Mexican-American War and transferred sovereignty over California from Mexico to America. After an extensive review of historical documents and testimonies, including evidence that suggested some irregularities with how the original grant had been processed, the court ruled against Pico's heirs who claimed ownership based on this grant. The justices concluded that while there were indeed flaws in how Mexican officials handled their duties at times, these did not invalidate all grants they issued or justify disregarding them entirely when determining property rights after sovereignty changed hands.

In the dissenting opinion for PICO v. United States, 1912, it was argued that the majority's decision to uphold a lower court ruling against Pico was incorrect. The dissent focused on two main points: first, they disagreed with the interpretation of Spanish law used by the majority and believed that under correct interpretation, Pico would have had a valid claim to his land; secondly, they felt there were procedural errors in how evidence was handled during trial which unfairly disadvantaged Pico. They contended that these issues combined resulted in an unjust outcome for Mr. Pico and therefore dissented from upholding his conviction.