Just after the organization of Esmeralda County, the vast majority of the land area had yet to be seen by Euro-American society. John C. Frémont was one of the few people who had explored parts of the county. He had crossed Big Smoky Valley in 1845. Also, Aurora and its northern corridor had been encountered. In 1862 and 1863, the area along the Reese River was explored during the Reese River excitement. The event resulted in the establishment of three mining districts in the Toiyabe Range, namely Marysville, Twin River, and Washington, and the establishment of a number of settlements and ranches in Esmeralda County. Explorers pursued south and explored the Shoshone Mountains. The mining district Union was organized after silver was found in 1863 and the settlement of Ione was founded there.