In 1848, California became part of the United States. Almost simultaneously, gold was discovered at Sutter's Mill. The great gold rush was on, luring hundreds then thousands then tens of thousands of '4gers to the gold country of the Sierra Nevada Mountains. On the coast, San Francisco was transformed from a remote military and missionary outpost into a major port, the point from which most adventurers disembarked to head for the mines. Ferry boats transported the miners from San Francisco up the Sacramento River to the Sierra foothills. From there, the miners pushed on, by pack mule or wagon or on foot into the mountains to search for gold.