Established July 20, 1962. Located west of the Medicine Bow River at the north base of Elk Mountain. The site was selected by and the post built under the command of Major John O'Ferrall, 11th Ohio Cavalry. It was established to protect the Overland Trail, the Denver-Salt Lake stage route, and the telegraph line from the Indians. Named for Major General Henry W. Halleck. Abandoned on July 4, 1866. The military reservation was transferred to the Interior Department on October, 11, 1886.
Dedicated to the men of the 11th Ohio Volunteer Cavalry. F. Mahannah is but one of the many stationed at Fort Halleck, 1862-1865. His name is one of many found carved in the nearby bluffs.