Fort Union, Mora County, N.M., was established in 1851 to protect settlers and travelers using the Santa Fe Trail, including some members of the Mormon Battalion. It was also used as a depot to supply other forts. This fort was actually three different posts in the same area, near the end of the Mountain Route just before it merged with the Cimarron Cutoff in Watrous, eight miles away.
As the railroad came, use of the Santa Fe Trail diminished, along with the need to protect those who utilized it. Moreover, pacification of the region in subsequent years led to the decision that Fort Union was no longer necessary and it was abandoned in 1891.
The majority of the members of the Mormon Battalion probably just missed Fort Union because they came on the Cimarron branch. However, some of those in sick detachments would likely have followed the Mountain Route to Fort Union and on to Pueblo, Colo.
Some good ruts of the trail remain to this day.