This map, produced in two parts in the early years after the California Gold Rush of 1849, shows the regions where gold was discovered in the territory. Accompanying the map was a 16-page appendix that gave further information on the location and significance of the gold strikes. The discovery of gold at Sutter’s Mill on the American River in January 1848 attracted migrants from the east coast of the United States, as well as from Europe, Central and South America, Australia, and Asia. The Treaty of Guadalupe Hidalgo ending the Mexican–American War, signed within two weeks of the discovery at Sutter’s Mill, made California a U.S. territory after centuries of control by Spain and Mexico. The influx of some 300,000 people accelerated the pace of political change in the territory. Elections, the drafting of a constitution, and the rapid achievement of statehood followed within a few years. The admission of California to the Union as a free state was a part of the Compromise of 1850, which was aimed at heading off a split between North and South over the issue of expanding slavery into the western territories. San Francisco, only a small village before the Gold Rush of 1849, became a boom town and then a significant metropolis. Captain William A. Jackson, the cartographer, was an engineer who had personal experience of the mines. The map and appendix shown here were published in 1851 and are revised from the first edition produced in 1850.