The massacre occurred in the southern Utah Territory at Mountain Meadows, and was perpetrated by settlers from the Church of Jesus Christ of Latter-day Saints (LDS Church) involved with the Utah Territorial Militia (officially called the Nauvoo Legion) who recruited and were aided by some Southern Paiute Native Americans.

A reminder in The Expanse books and TV series the Mormon generational ship is called the Nauvoo.

The wagon train, made up mostly of immigrant families from Arkansas, was bound for California, traveling on the Old Spanish Trail that passed through the Territory.

Because evidently celebrating the massacre of families is something worth doing in both modern writing, and a setting hundreds of years in the future.