Greenhorn was first populated in the 1860s as miners prospected for gold in the area. It was
platted in 1904, though it lost two-thirds of its population between 1900 and 1910. The mining district was composed first of placer mines, but soon many lode gold mines developed. The city was incorporated in 1903 and had a population of 28 in 1910. It continued as a viable community until 1942 when gold mining was made illegal by Federal Public Law 208 during
World War II. In later years, the old Greenhorn Jail (dating to around 1910) was removed to
Canyon City under suspicious circumstances. A court case ensued for its return, but because the city straddles the Blue Mountain ridge, the district attorneys of Baker County and Grant County could not even agree in which court house it should be held. The case was eventually heard by the Circuit Court for Grant County in Canyon City, Oregon. The jail remains in Canyon City, Oregon. ==Geography==