 It is named after the Ida Elmore mines, the area's greatest silver and gold producer of the 1860s, located near Silver City in Owyhee County.While the Oregon Trail crossed the Snake River in Elmore County, at Three Island Crossing near Glenns Ferry, the significant early settlements of Elmore County were mining settlements located primarily in northern Elmore County surrounding the ghost town of Rocky Bar.Settlement at Rocky Bar commenced in 1863 with the settlement having 560 residents at the Territorial Census of that year.