In 1846, Thomas Larkin, American council general to the Mexican government in California, purchased a Mexican land grant, Las Mariposas, for Col. John C. Fremont. The grant consisted of 10 square leagues of grazing land located near the Merced River and west of the Sierra. In 1848, when California became the possession of the United States, the treaty called for the recognition of preexisting grants. Gold was discovered in the foothills of the Sierra...