El Dorado, "The Gilded One", was first known as Mud Springs from the boggy quagmire the cattle and horses made of a nearby watering place. Originally an important camp on the old Carson Trail, by 1849-50 it had become the center of a mining district and the crossroads for freight and stagecoach lines. At the height of the rush its large gold production supported a population of several thousand. It was incorporated as the town of El Dorado in 1856.

The first post office in Mud Spring was opened in 1851, the name was changed to El Dorado in 1855.