Fort Union National Monument is a unit of the United States National Park Service, and is located north of Watrous in New Mexico. The national monument was founded on June 28, 1954.

The monument site preserves the second of three forts that were constructed on this site as well as the ruins of the third fort. 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). There is a 1.2 mile (1.9 km) long trail which winds through the adobe ruins of the third fort.

The first Fort Union was constructed to provide protection from hostile indigenous tribes for travelers and people living in the vicinity along the Santa Fe Trail. The first fort was called a frontier fort, which is described as more open campuses, places to house and feed soldiers, rather than a traditional defense structure.

The second fort was the more traditional defense structure of the three and was built with the purpose of defending against an invasion of the Confederate army. The soldiers from the fort united with the volunteer army from Colorado to hold back the Confederates in the Battle of Glorieta Pass.

The third Fort Union was, like the first, a frontier fort and not used for defense, but as a supply base to hold and distribute different types of goods such as ammunition, clothing, food, and more. The third Fort Union is the one available for touring and was constructed with native materials such as clay, stone, and lumber, adobe brick was used for the walls and was coated in plaster.

The third fort was abandoned by the military due to the conclusion of the American Indian Wars and the formation of the Santa Fe Railroad.

In the early days, it was the Utes and Jicarilla Apaches who lived in the area around the fort and were the predominant tribes that kept soldiers constantly engaged.

Santa Fe Trail