Fort Union National Monument is a unit of the National Park Service located north of Watrous, Mora County, New Mexico, USA. 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.
There is a visitor center with exhibits about the fort and a film about the Santa Fe Trail. The altitude of the Visitor Center is 6760 feet (2060 m). A 1.2-mile (1.9-kilometre) trail winds through the fort's adobe ruins.