Mariposa was founded as a mining camp on Aqua Fria Creek, but after the 1849/50 winter floods and a fire, the town was removed to its present location some six miles east to a better terrain, and a larger source of placer gold, on Mariposa Creek. Its name is Spanish for “butterfly,” and was so named by early Spanish explorers for the swarms of monarch butterflies they saw there. The populace moved to the new boom town, and soon the large Mariposa mine opened, with a 40-foot waterwheel crushing gold ore. This provided a stable source of employment, and Mariposa became the supply hub for hundreds of outlying mining districts as the era of hard rock mining began in 1851. That year Mariposa was named the county seat of Mariposa County, at the time the largest county in California measured by land area. Explorer John Charles Fremont owned the Mexican land grant Rancho Las Mariposas that gave him ownership of the Mariposa mining district—and although he did become rich—the influx of hordes of miners made policing his property impossible. By 1854 Mariposa had a grand courthouse, now the oldest courthouse in California still in use. The town’s residents have preserved some of the features of early mining camps: buildings with substantial walls of brick and stone supplemented by iron doors and shutters to retard fire winds. The Mariposa County Library and History Center contains furniture belonging to the Fremont family, displays of Indian material, 1900s-era businesses, and exhibits connected with mining activities that make it one of the most comprehensive collections in the Mother Lode country.