Fort Union National Monument is a unit of the National Park Service of the United States, and is located north of Watrous in Mora County, New Mexico. The national monument was founded on June 28, 1954. The site preserves the second of three forts constructed on the site beginning in 1851, as well as the ruins of the third. Also visible is a network of ruts from the Mountain and Cimarron Branches of the old Santa Fe Trail.