Fort Halleck was established on July 20, 1862, west of the Medicine Bow River at the north base of Elk Mountain. The site was selected and the post built under the command of Major John O'Ferrall of the 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, it was abandoned on July 4, 1866. The military reservation was transferred to the Interior Department on October 11, 1886. Men of the 11th Ohio Volunteer Cavalry were stationed there, including F. Mahannah, whose name is one of many carved in the nearby bluffs from 1862 to 1865.