Following the United States' acquisition of California under the 1848 Treaty of Guadalupe-Hidalgo, Congress passed "An Act to ascertain and settle the private Land Claims in the State of California." This statute established a commission to determine the status of the approximately 750 land grants that Spanish and Mexican authorities had made to private individuals before 1848. Congress provided that the commission and courts should evaluate the validity of the grants by, among other criteria, "the laws, usages, and customs of the government from which the claim is derived, the principles of equity, and the decisions of the Supreme Court of the United States." The act thus generated a critical tension between the American and Mexican approaches to the law of land grants. American law in this area was precise and meticulous, demanding strict compliance with written requirements. By contrast, Spanish and Mexican officials generally did not treat written law with the same degree of sanctity as their American counterparts, instead relying heavily on customary law. The conflict between law and custom in the determination of ownership of the California land grants was further complicated by the fact that Mexican customs, developed over years of slow growth and minimal pressure on resources, seemed anachronistic after the discovery of gold in California in 1848 and the consequent rise in population and land values. This article explores how these cultural and temporal tensions played out in the important dispute concerning the ownership of a grant claimed by John C. Fremont--a dispute ultimately resolved in Fremont's favor by the United States Supreme Court in 1854.
Grossman, Lewis A., John C. Fremont, Mariposa, and the Collision of Mexican and American Law. Western Legal History, Vol. 6, p. 17, 1993.